• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

1999 XJ - when is cruise control light SUPPOSED to light?

soyjer

NAXJA Forum User
Location
California
1999 stock XJ - just a very basic question:

Is the cruise control light supposed to come on when I simply initially insert the key and then turn the key to "RUN" position (but NOT "START") to test the bulb, along with all of the other bulbs that come on to be tested then?

How about if, immediately after doing the above, I then press the cruise control on/off button...should the cruise control lamp come on then?

How about after the engine is started, but the vehicle is still stationary?

I've read many posts regarding this subject and have checked my vacuum system and brake light switch, horn, etc., but if I knew for a fact that the cruise control bulb is supposed to light while the vehicle is stationary under ANY of the above circumstances, it would make troubleshooting the problem a lot easier, since I could then troubleshoot why the light isn't coming on without having to drive the vehicle over 35 mph to do so.

Thanks
 
Just checked on my '98, only time the light came on was with the vehicle started and pushing the button.

Did not come on with the switch to run and pushing the button, or with all the other lamps after engine start.

Sent from my SAMSUNG-SM-G891A using Tapatalk
 
Just checked on my '98, only time the light came on was with the vehicle started and pushing the button.

Did not come on with the switch to run and pushing the button, or with all the other lamps after engine start.

Sent from my SAMSUNG-SM-G891A using Tapatalk

same as above on my 98
 
Just checked on my '98, only time the light came on was with the vehicle started and pushing the button.

Did not come on with the switch to run and pushing the button, or with all the other lamps after engine start.

Sent from my SAMSUNG-SM-G891A using Tapatalk

Thank you for your answers... Now I know that I probably need to have the engine running when I check for the presence of the PCM supplied cruise control power at the brake switch and at the servo. I haven't found a circuit diagram that contains the cruise control light yet, but it's probably a safe bet that the cruise control light corresponds to when the PCM supplies power through the brake switch to the servo...I guess.
 
Have you checked if the bulb is failed ? FYI cruise control switch failure is somewhat common and a logical place to begin diagnostics.
 
My switch is intermittent. Some days works fine, some days I have to get it just right. I would start there before getting too deep in the weeds.

Sent from my SAMSUNG-SM-G891A using Tapatalk
 
I may have a set of switches -- I bought a set on Ebay, where supposed to be for a 2000 but they weren't -- I forget exactly which year they are -- If interested I'll check

I do know the plastic mounting tab is broken on at least one of the switches -- Was a bad deal on ebay, seller didn't want item back
 
My switch is intermittent. Some days works fine, some days I have to get it just right. I would start there before getting too deep in the weeds.

Sent from my SAMSUNG-SM-G891A using Tapatalk

According to wiring diagram 8W - 33 - 2, pressing the speed control switch on/off button connects the following PCM pins directly together electrically, and should therefore cause the voltage between them to drop to 0 volts (presumably from 12 volts):

Pin C32, Connector C3, RD/LG, SPEED CONTROL SWITCH SIGNAL

Pin A4, Connector C1, BR/YL, SENSOR GROUND

Luckily for troubleshooting the on/off switch, the on/off button switch connects these pins DIRECTLY together electrically (the other four speed control button switch circuits have varying resistances in them), and so the voltage measured above should go from full voltage (again, presumably 12 volts) to 0 volts, and not to any intermediate voltage.

Now I just have to figure out if there is any way to gain access to those measuring points.
 
Pin C32, Connector C3, RD/LG, SPEED CONTROL SWITCH SIGNAL is actually +5 volts (not +12 volts) with respect to Pin A4, Connector C1, BR/YL, SENSOR GROUND.

I checked all signal paths involved with speed control and brake sensing, and they are all fine, and the brake lamp switch tests OK, and so if the above pins are momentarily connected together with the engine running, then normally the cruise control lamp should come on and the speed control power supply voltage should be provided to the speed control servo through the brake lamp switch, but for some reason my cruise control lamp does not come on, and and the speed control power supply voltage is not provided to the speed control servo through the known good brake lamp switch.

The speed control switches have no continuity through the clockspring, and so I am momentarily shorting the above two pins together using a jumper cable, but I am electrically simulating the use of the speed control on/off switch, and so it doesn't seem as if it should matter HOW the pins are touched together, only that they ARE being touched together, and so I am reluctant to blame the clockspring for this problem. I'm starting to wonder if this PCM is a replacement from an XJ that did not have cruise control? But I've heard of XJ owners adding factory cruise controls to their non-factory cruise control XJ's successfully, so how could they do that if the PCM's on non-factory cruise control XJ's lack the programming necessary to operate the cruise control function?
 
Cruise control is plug and play, no matter what options were originally installed, or not installed, at the Jeep factory.
 
Cruise control is plug and play, no matter what options were originally installed, or not installed, at the Jeep factory.

OK...thanks...that would seem to make sense because people do seem to be able to retrofit factory cruise control without replacing their PCM's.

Which leaves me with a dilemma... All of my wiring and components seem to be in perfect working order (except clockspring, see below) and yet the PCM refuses to supply the "speed control power supply" +5 volts when the above-mentioned on/off pins are momentarily touched together and the engine is running.

I can only think of three things that could be happening:

1. The PCM pin that supplies the speed control power supply is shorted to ground.
...NOPE, 23K ohms on DVM.

2. The PCM itself is working perfectly in absolutely every other way except for the speed control function.
..POSSIBLE, I SUPPOSE.

3. I am misinterpreting the wiring diagram 8W - 33 - 2 as far as how the speed control on/off switch functions. I interpret that wiring diagram as showing that the on/off switch merely momentarily touches those two pins together to turn the speed control on/off (assuming that all other conditions required by the PCM are satisfied).
Is it somehow more complicated than that?

FULL DISCLOSURE: There is no continuity between my speed control on/off switch and those pins...which would indicate that my clock spring needs replacing...but before I replace the clock spring, I was hoping to verify that the cruise control system would at least turn on, sitting still with the engine running, to give me some degree of confidence that the cruise control system may actually work after I replace the clockspring.
the horn works, by the way, and there is no airbag light lit, so those circuits do seem to be making it successfully through the clock spring.

Chrysler calls the way the speed control switches communicate with the PCM "Resistive Multiplexing"...using just two wires and varying resistances to communicate to the PCM which button or buttons are currently being pressed, with the on/off function being ~ zero resistance. It seems relatively simple, unless I am missing something.
 
... All of my wiring and components seem to be in perfect working order (except clockspring, see below)

The clock springs needs to be fully functional and the steering wheel switches have to be the correct version for your model year. You should bypass the clock spring and the suspect wires with a test wire.

You will need to understand and follow the clock spring safety procedures.




AIRBAG and CLOCK SPRING

SYSTEM OPERATION

The clock spring is mounted on the steering column behind the steering wheel. This assembly consists of a plastic housing which contains a flat, ribbon-like, electrically conductive tape that winds and unwinds with the steering wheel rotation.

The clock spring is used to maintain a continuous electrical circuit between the instrument panel wire harness and the driver side airbag module, the horn switch, and the vehicle speed control switches on vehicles that are so equipped.

The clock spring must be properly centered when it is installed on the steering column following any service removal, or it will be damaged. See the Clock spring Centering procedure for more information.

The clock spring cannot be repaired. If the clock spring is faulty, damaged, or if the airbag has been deployed, the clock spring must be replaced.

WARNING: THE AIRBAG SYSTEM IS A SENSITIVE, COMPLEX ELECTROMECHANICAL UNIT. BEFORE ATTEMPTING TO DIAGNOSE OR SERVICE ANY AIRBAG SYSTEM OR RELATED STEERING WHEEL, STEERING COLUMN, OR INSTRUMENT PANEL COMPONENTS YOU MUST FIRST DISCONNECT AND ISOLATE THE BATTERY NEGATIVE (GROUND) CABLE. THEN WAIT TEN MINUTES FOR THE SYSTEM CAPACITOR TO DISCHARGE BEFORE FURTHER SYSTEM SERVICE. THIS IS THE ONLY SURE WAY TO DISABLE THE AIRBAG SYSTEM. FAILURE TO DO THIS COULD RESULT IN ACCIDENTAL AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL INJURY.

XJ PASSIVE RESTRAINT SYSTEMS

REMOVAL AND INSTALLATION
(1) Turn the steering wheel until the front wheels are in the straight-ahead position before starting the procedure.
(2) Disconnect and isolate the battery negative cable. If the airbag has not been deployed, wait ten minutes for the system capacitor to discharge before further service.
(3) Remove the driver side airbag module as described in this group.
(4) If the vehicle is equipped with the optional vehicle speed control, unplug the speed control switch wire harness connector in the steering wheel.
(5) Remove the nut that secures the steering wheel to the steering column upper shaft.
(6) Remove the steering wheel with a steering wheel puller.
(7) Remove the steering column opening cover.
(8) If the vehicle is so equipped, move the tilt steering column to the fully raised position.

(STEPS 9,10,11 are optional and performed only if required)

(9) Insert the key in the ignition lock cylinder and turn the ignition switch to the On position.
(10) Insert a small screwdriver or pin punch through the access hole in the lower steering column shroud and depress the ignition lock cylinder retaining tumbler (Fig. 13).
(11) While holding the retaining tumbler depressed, pull the ignition lock cylinder and key out of the ignition lock housing.
(12) Remove the three screws that secure the lower steering column shroud to the upper shroud.
(13) If the vehicle is equipped with a standard non-tilt steering column, loosen the two upper steering column mounting nuts. If the vehicle is equipped with the optional tilt steering column, move the tilt steering column to the fully lowered position.
(14) Remove both the upper and lower shrouds from the steering column.
(15) Unplug the two wire harness connectors from the steering column side of the clockspring.
(16) To remove the clockspring, carefully lift the locating fingers of the clockspring assembly from the steering column as necessary. If the clockspring locating fingers are broken, be certain to remove the broken pieces from the upper steering column housing. The clockspring cannot be repaired. It must be replaced if faulty or damaged, or if the airbag has been deployed.
(17) When installing the clockspring, snap the clockspring onto the steering column. If the clockspring is not properly positioned, see Clockspring Centering in this group before installing the steering wheel.
(18) Plug the two clockspring wire harness connectors into the steering column side of the clockspring. Be certain that the wire harness connector latches are fully engaged.
(19) Reinstall the steering column shrouds and ignition lock cylinder.
(20) Reinstall the steering column opening cover as described in Group 8E - Instrument Panel Systems.
(21) The front wheels should still be in the straight-ahead position. Install the steering wheel being certain to fit the flats on the hub of the steering wheel onto the formations on the inside of the clockspring. Pull the wire harness through the lower hole in the steering wheel hub. Tighten the steering wheel nut to 61 N·m (45 ft. lbs.). Be certain not to pinch the wiring between the steering wheel and the nut.
Install the airbag module as described in this group.


ADJUSTMENTS
CLOCKSPRING CENTERING

If the rotating tape within the clockspring is not positioned properly in relation to the steering wheel and the front wheels, the clockspring may fail during use. The clockspring must be centered if it is not known to be properly positioned, or if the front wheels were moved from the straight-ahead position with the clockspring removed during any service procedure.

WARNING: THE AIRBAG SYSTEM IS A SENSITIVE, COMPLEX ELECTROMECHANICAL UNIT. BEFORE ATTEMPTING TO DIAGNOSE OR SERVICE ANY AIRBAG SYSTEM OR RELATED STEERING WHEEL, STEERING COLUMN, OR INSTRUMENT PANEL COMPONENTS YOU MUST FIRST DISCONNECT AND ISOLATE THE BATTERY NEGATIVE (GROUND) CABLE. THEN WAIT TEN MINUTES FOR THE SYSTEM CAPACITOR TO DISCHARGE BEFORE FURTHER SYSTEM SERVICE. THIS IS THE ONLY SURE WAY TO DISABLE THE AIRBAG SYSTEM. FAILURE TO DO THIS COULD RESULT IN ACCIDENTAL AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL INJURY.

(1) Turn the steering wheel until the front wheels are in the straight-ahead position before starting the centering procedure.
(2) Disconnect and isolate the battery negative cable. If the airbag has not been deployed, wait ten minutes for the system capacitor to discharge before further service.
(3) Remove the airbag module as described in this group.
(4) If the vehicle is equipped with the optional vehicle speed control, unplug the speed control switch wire harness connector in the steering wheel.
(5) Remove the nut that secures the steering wheel to the steering column upper shaft.
(6) Remove the steering wheel with a steering wheel puller (Special Tool C-3428B).
(7) Rotate the clockspring rotor clockwise to the end of its travel (Fig. 14). Do not apply excessive torque.
(8) From the end of the clockwise travel, rotate the rotor about two and one-half turns counterclockwise, until the rotor flats are horizontal. If the clockspring wire harness is not at the bottom, rotate another one-half turn.
(9) The front wheels should still be in the straightahead position. Install the steering wheel being certain to fit the flats on the hub of the steering wheel onto the formations on the inside of the clockspring. Pull the wire harness from the clockspring through the lower hole in the steering wheel hub. Tighten the steering wheel nut to 61 N·m (45 ft. lbs.). Be certain not to pinch any of the wiring between the steering wheel and the nut.
(10) Install the airbag module as described in this group.
 
Last edited:
Have you checked if the bulb is failed ? FYI cruise control switch failure is somewhat common and a logical place to begin diagnostics.

No..only because without speed control power voltage being supplied by the PCM, there is no way that the cruise control lamp could ever legitimately light up.
 
The clock springs needs to be fully functional. I suppose you could bypass the clock spring and the suspect wires with a test wire You will need to understand and follow the clock spring safety procedures.

Thanks for the clockspring procedure... If I can prove to myself that the cruise control system will actually function with a new clock spring, then I will need that procedure...thanks.

Pins 2 & 3 of connector C1 under the steering column connect directly to the clock spring, then through the clock spring to the speed control switches, and so it would seem that just momentarily shorting them together with the engine running would cause the PCM to provide +5 volt speed control power supply voltage to the system (assuming the brake switch works okay, etc), but in my case the PCM is not supplying that speed control power supply voltage. I'm hoping someone familiar with Chrysler's resistive multiplexing will chime in to confirm that my assumption about these pins and how resistive multiplexing works is correct. If my assumption is correct, that merely touching these pins together under the right conditions should cause the speed control power supply voltage to be provided to the system, then, based on the fact that my system seems to be in perfect working order other than this issue, The logical conclusion would be that my PCM functions perfectly in every other way except that for some reason only the cruise speed control function is not working in the PCM. I checked my PCM model number 56041492AE and it is, indeed, the correct one for a federal 1999 Jeep Cherokee XJ with automatic transmission and 4.0 liter engine.


AIRBAG and CLOCK SPRING

SYSTEM OPERATION

The clock spring is mounted on the steering column behind the steering wheel. This assembly consists of a plastic housing which contains a flat, ribbon-like, electrically conductive tape that winds and unwinds with the steering wheel rotation.

The clock spring is used to maintain a continuous electrical circuit between the instrument panel wire harness and the driver side airbag module, the horn switch, and the vehicle speed control switches on vehicles that are so equipped.

The clock spring must be properly centered when it is installed on the steering column following any service removal, or it will be damaged. See the Clock spring Centering procedure for more information.

The clock spring cannot be repaired. If the clock spring is faulty, damaged, or if the airbag has been deployed, the clock spring must be replaced.

WARNING: THE AIRBAG SYSTEM IS A SENSITIVE, COMPLEX ELECTROMECHANICAL UNIT. BEFORE ATTEMPTING TO DIAGNOSE OR SERVICE ANY AIRBAG SYSTEM OR RELATED STEERING WHEEL, STEERING COLUMN, OR INSTRUMENT PANEL COMPONENTS YOU MUST FIRST DISCONNECT AND ISOLATE THE BATTERY NEGATIVE (GROUND) CABLE. THEN WAIT TEN MINUTES FOR THE SYSTEM CAPACITOR TO DISCHARGE BEFORE FURTHER SYSTEM SERVICE. THIS IS THE ONLY SURE WAY TO DISABLE THE AIRBAG SYSTEM. FAILURE TO DO THIS COULD RESULT IN ACCIDENTAL AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL INJURY.

XJ PASSIVE RESTRAINT SYSTEMS

REMOVAL AND INSTALLATION
(1) Turn the steering wheel until the front wheels are in the straight-ahead position before starting the procedure.
(2) Disconnect and isolate the battery negative cable. If the airbag has not been deployed, wait ten minutes for the system capacitor to discharge before further service.
(3) Remove the driver side airbag module as described in this group.
(4) If the vehicle is equipped with the optional vehicle speed control, unplug the speed control switch wire harness connector in the steering wheel.
(5) Remove the nut that secures the steering wheel to the steering column upper shaft.
(6) Remove the steering wheel with a steering wheel puller.
(7) Remove the steering column opening cover.
(8) If the vehicle is so equipped, move the tilt steering column to the fully raised position.

(STEPS 9,10,11 are optional and performed only if required)

(9) Insert the key in the ignition lock cylinder and turn the ignition switch to the On position.
(10) Insert a small screwdriver or pin punch through the access hole in the lower steering column shroud and depress the ignition lock cylinder retaining tumbler (Fig. 13).
(11) While holding the retaining tumbler depressed, pull the ignition lock cylinder and key out of the ignition lock housing.
(12) Remove the three screws that secure the lower steering column shroud to the upper shroud.
(13) If the vehicle is equipped with a standard non-tilt steering column, loosen the two upper steering column mounting nuts. If the vehicle is equipped with the optional tilt steering column, move the tilt steering column to the fully lowered position.
(14) Remove both the upper and lower shrouds from the steering column.
(15) Unplug the two wire harness connectors from the steering column side of the clockspring.
(16) To remove the clockspring, carefully lift the locating fingers of the clockspring assembly from the steering column as necessary. If the clockspring locating fingers are broken, be certain to remove the broken pieces from the upper steering column housing. The clockspring cannot be repaired. It must be replaced if faulty or damaged, or if the airbag has been deployed.
(17) When installing the clockspring, snap the clockspring onto the steering column. If the clockspring is not properly positioned, see Clockspring Centering in this group before installing the steering wheel.
(18) Plug the two clockspring wire harness connectors into the steering column side of the clockspring. Be certain that the wire harness connector latches are fully engaged.
(19) Reinstall the steering column shrouds and ignition lock cylinder.
(20) Reinstall the steering column opening cover as described in Group 8E - Instrument Panel Systems.
(21) The front wheels should still be in the straight-ahead position. Install the steering wheel being certain to fit the flats on the hub of the steering wheel onto the formations on the inside of the clockspring. Pull the wire harness through the lower hole in the steering wheel hub. Tighten the steering wheel nut to 61 N·m (45 ft. lbs.). Be certain not to pinch the wiring between the steering wheel and the nut.
Install the airbag module as described in this group.


ADJUSTMENTS
CLOCKSPRING CENTERING

If the rotating tape within the clockspring is not positioned properly in relation to the steering wheel and the front wheels, the clockspring may fail during use. The clockspring must be centered if it is not known to be properly positioned, or if the front wheels were moved from the straight-ahead position with the clockspring removed during any service procedure.

WARNING: THE AIRBAG SYSTEM IS A SENSITIVE, COMPLEX ELECTROMECHANICAL UNIT. BEFORE ATTEMPTING TO DIAGNOSE OR SERVICE ANY AIRBAG SYSTEM OR RELATED STEERING WHEEL, STEERING COLUMN, OR INSTRUMENT PANEL COMPONENTS YOU MUST FIRST DISCONNECT AND ISOLATE THE BATTERY NEGATIVE (GROUND) CABLE. THEN WAIT TEN MINUTES FOR THE SYSTEM CAPACITOR TO DISCHARGE BEFORE FURTHER SYSTEM SERVICE. THIS IS THE ONLY SURE WAY TO DISABLE THE AIRBAG SYSTEM. FAILURE TO DO THIS COULD RESULT IN ACCIDENTAL AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL INJURY.

(1) Turn the steering wheel until the front wheels are in the straight-ahead position before starting the centering procedure.
(2) Disconnect and isolate the battery negative cable. If the airbag has not been deployed, wait ten minutes for the system capacitor to discharge before further service.
(3) Remove the airbag module as described in this group.
(4) If the vehicle is equipped with the optional vehicle speed control, unplug the speed control switch wire harness connector in the steering wheel.
(5) Remove the nut that secures the steering wheel to the steering column upper shaft.
(6) Remove the steering wheel with a steering wheel puller (Special Tool C-3428B).
(7) Rotate the clockspring rotor clockwise to the end of its travel (Fig. 14). Do not apply excessive torque.
(8) From the end of the clockwise travel, rotate the rotor about two and one-half turns counterclockwise, until the rotor flats are horizontal. If the clockspring wire harness is not at the bottom, rotate another one-half turn.
(9) The front wheels should still be in the straightahead position. Install the steering wheel being certain to fit the flats on the hub of the steering wheel onto the formations on the inside of the clockspring. Pull the wire harness from the clockspring through the lower hole in the steering wheel hub. Tighten the steering wheel nut to 61 N·m (45 ft. lbs.). Be certain not to pinch any of the wiring between the steering wheel and the nut.
(10) Install the airbag module as described in this group.
 
When I added CC to my ‘00 TJ I had to add/replace:
- clock spring (mine was non-CC)
- servo
- buttons that were year specific to the year
- wiring harness to connect buttons to clock spring
After all that it was plug and play.


Sent from my iPhone using Tapatalk
 
I have a new theory as to how the speed control system works that would explain why merely touching the clock spring pins together in a system working perfectly would NOT cause the PCM to supply the speed control power supply voltage to the system:

I was previously assuming that touching those two pins together, simulating a speed control switch on /off switch press, would cause the PCM to supply the speed control power supply voltage to the system, and then after that pressing any of the other speed control (resistive) switches would then actually cause the speed control system to perform a function, according to which switch was pressed.

But I think my error was in thinking that the speed control power supply voltage was merely a power supply that merely made power available to the system and did nothing on its own. Now I am thinking that the speed control power supply is not just a power supply but is actually the power that directly operates the system, and so it should only be present when the system is actually engaged and performing its speed control function.

I am therefore now also theorizing that the speed control on/off switch by itself does not cause the PCM to take any action that could be externally measured at all, but instead merely alerts the PCM internally to "obey / not obey" future resistive switch presses.

If my new theories are correct, that would explain why merely touching those on/off pins together would NOT cause the PCM to supply the speed control power supply voltage to the system.

In order to cause the PCM to supply the speed control power supply voltage to the system, I would have to be able to first touch the on/off pins together to alert the PCM to be on the lookout for future resistive switch button presses, and then be able to connect a resistor momentarily between those pins that matched the resistance of the speed control SET switch button. And I'm guessing that while doing all this I would also have to be driving the vehicle above 37 miles per hour in order for the PCM to actually supply that speed control power supply voltage to the system.

If I knew what resistance the set button switch contained, I could actually do the above with a passenger helper, but the wiring diagram does not specify what the various resistances are of those steering wheel switches, so I guess my next step would be to carefully and safely remove the airbag, and then remove the speed control switches, and then connect the speed control switches directly up to speed control pins, bypassing the clock spring, and if the system works perfectly that way then replace the clockspring. If the system does not function properly that way, then maybe I could compare resistance measurements of my switches against a known good switch set to determine if the switches are bad or not, or buy a returnable switch set to determine if my switch set is bad or not.

I know that these clock springs are notorious for going bad, but my horn works and I have no airbag light nor OBD2 code, and I have no idea whether the cruise control system itself works or not because this is a new vehicle to me, and so I am reluctant to just throw in a new clock spring based on a whole lot of speculation with regard to if I'm trying to operate an otherwise broken system or not and also speculation as far as to whether my theories of how the system works are correct or not.

I'm hopeful that bypassing the clockspring will cause the system to work perfectly, and then I will know for sure that the clockspring merely needs replacing.

If possible, I would like to do this testing with the airbag out of the car...does anybody know if removing the airbag from a 1999 Jeep Cherokee XJ will cause the car to not function?
 
The clock springs needs to be fully functional. I suppose you could bypass the clock spring and the suspect wires with a test wire You will need to understand and follow the clock spring safety procedures.

I have a new theory as to how the speed control system works that would explain why merely touching the clock spring pins together in a system working perfectly would NOT cause the PCM to supply the speed control power supply voltage to the system:

I was previously assuming that touching those two pins together, simulating a speed control switch on /off switch press, would cause the PCM to supply the speed control power supply voltage to the system, and then after that pressing any of the other speed control (resistive) switches would then actually cause the speed control system to perform a function, according to which switch was pressed.

But I think my error was in thinking that the speed control power supply voltage was merely a power supply that merely made power available to the system and did nothing on its own. Now I am thinking that the speed control power supply is not just a power supply but is actually the power that directly operates the system, and so it should only be present when the system is actually engaged and performing its speed control function.

I am therefore now also theorizing that the speed control on/off switch by itself does not cause the PCM to take any action that could be externally measured at all, but instead merely alerts the PCM internally to "obey / not obey" future resistive switch presses.

If my new theories are correct, that would explain why merely touching those on/off pins together would NOT cause the PCM to supply the speed control power supply voltage to the system.

In order to cause the PCM to supply the speed control power supply voltage to the system, I would have to be able to first touch the on/off pins together to alert the PCM to be on the lookout for future resistive switch button presses, and then be able to connect a resistor momentarily between those pins that matched the resistance of the speed control SET switch button. And I'm guessing that while doing all this I would also have to be driving the vehicle above 37 miles per hour in order for the PCM to actually supply that speed control power supply voltage to the system.

If I knew what resistance the set button switch contained, I could actually do the above with a passenger helper, but the wiring diagram does not specify what the various resistances are of those steering wheel switches, so I guess my next step would be to carefully and safely remove the airbag, and then remove the speed control switches, and then connect the speed control switches directly up to speed control pins, bypassing the clock spring, and if the system works perfectly that way then replace the clockspring. If the system does not function properly that way, then maybe I could compare resistance measurements of my switches against a known good switch set to determine if the switches are bad or not, or buy a returnable switch set to determine if my switch set is bad or not.

I know that these clock springs are notorious for going bad, but my horn works and I have no airbag light nor OBD2 code, and I have no idea whether the cruise control system itself works or not because this is a new vehicle to me, and so I am reluctant to just throw in a new clock spring based on a whole lot of speculation with regard to if I'm trying to operate an otherwise broken system or not and also speculation as far as to whether my theories of how the system works are correct or not.

I'm hopeful that bypassing the clockspring will cause the system to work perfectly, and then I will know for sure that the clockspring merely needs replacing.

If possible, I would like to do this testing with the airbag out of the car...does anybody know if removing the airbag from a 1999 Jeep Cherokee XJ will cause the car to not function?
 
Correction: according to the FSM, the owners manual, and people in this forum, the CRUISE lamp on the dash should light up as soon as the on-off switch is pressed as long as the engine is running. So apparently the PCM does, after all, have an external signal that can be detected after just pressing the on-off switch alone while the engine is running. If true, this is different than other vehicles I have owned, where the cruise lamp only was lit when the cruise control was actually functioning and controlling speed while driving. To me, the latter makes more sense, because then the cruise lamp tells you whether the PCM is controlling your speed or not while you are driving.

This is what the FSM says regarding the cruise lamp, and the owner's manual agrees:

"A speed control indicator lamp, located on the
instrument panel cluster, is energized by the PCM via
the J1850 PCI Bus circuits. This occurs when speed
control system power has been turned ON, and the
engine is running."

Can someone else please confirm that their CRUISE lamp lights with a mere press of the speed control on/off switch with the engine running and the vehicle sitting still in Park, and without having to press any other buttons, including the SET button?

I've already received confirmation that this is true, but because it to me it makes no sense I feel that I should make completely sure that it operates in this seemingly strange way before I proceed troubleshooting based upon this.

Can anyone figure out and tell me why Chrysler would design this such that the CRUISE light comes on like this instead of indicating when the vehicle is actually being controlled by the speed control system?
 
BTW, I was able to verify that the cruise lamp and cruise lamp circuit from the PCM are functional, using the following procedure. This of course doesn't tell me if the speed control system is working or not, but at least I will know that if the PCM tries to turn the cruise control lamp on, it should be able to:

"(1) Begin the test with the ignition switch in the
Off position.
(2) Depress the trip odometer reset button.
(3) While holding the trip odometer reset button
depressed, turn the ignition switch to the On posi-
tion, but do not start the engine.
(4) Release the trip odometer reset button.
(5) Compare the operation of the suspect gauge(s)
and/or indicator lamp(s) with the Instrument Cluster
Actuator Test chart (Fig. 1) or (Fig. 2).
(6) The instrument cluster will automatically exit
the self-diagnostic mode and return to normal opera-
tion at the completion of the test, if the ignition
switch is turned to the Off position during the test,
or if a vehicle speed message indicating that the
vehicle is moving is received from the PCM on the
CCD data bus during the test."
 
I would start by checking continuity through the clock spring after you remove the airbag. You can also check the part numbers on your switches to make sure they’re correct for your rear vehicle.


Sent from my iPhone using Tapatalk
 
Back
Top