99 XJ engine stall when blower turned on

[McQue]

THE A/C SELECT SWITCH SENSE AND BRAKE LAMP SWITCH SENSE SEEM TO BE INTERACTING... THOSE TWO SIGNAL LINES TO THE PCM ARE AT CONNECTOR C3 OF THE PCM PINS 23 AND 24. YOU MIGHT WANT TO DISCO THAT CONNECTOR, AND INSPECT THE PINS ...MAYBE THEY ARE SHORTED TOGETHER AT THAT POINT OR SOMEWHERE IN THE WIRING LOOM.

 

[Automechnic077]

I checked the pins and pin outs everything looks kosher. Prior to cutting into the wiring loom and looking for shorts. I deceided to take out the ac controls and radio this morning to assure myself I didn't squish anything when putting stuff back together. When unplugging the plug for the ac controls guess what truck dies. :sure: . Perhaps that's normal because I just spent 10 minutes trying to get the codes from the computer with a no communication's error. Doh. I didn't plug the ac controls back in!
Hot off the press I have. P0505 IAC AIS motor circuits shorted. (It's been this code since day one of me owning it).
And P0700 Trans fault present
Trans code P1694 CCD message from JTEC failure.
Is it possible to pull the wire from the pcm plug then also on the destination side and just create a jumper to test rather than cut and splice stuff?

 

[Sidewinder CC]

Is the part number on your PCM 56041 492AC?

Hint Hint

 

[Automechnic077]

Is the part number on your PCM 56041 492AC?

Hint Hint

Sorry the hint hint doesn't ring any bells, I'm new to xj's
I read AD is low emissions no security...
P56041 493AD is my Motorola PCM

 

[Sidewinder CC]

Sorry the hint hint doesn't ring any bells, I'm new to xj's
I read AD is low emissions no security...
P56041 493AD is my Motorola PCM

Google the word "Hint".

With a 493AD is California Emissions.

Do you have the Sentry Key Immobilizer System? If so, any replacement PCM must be programmed for it.

 

[Automechnic077]

Ok so your hinting my PCM may be bad.
I have the black keys so I dont believe I need the sentry system.
Where is the best place to get one of these pcm's?

 

[Automechnic077]

Would it make sense to diagnose another issue I'm having to be sure it's a pcm?

 

[Sidewinder CC]

What other issue?

 

[Automechnic077]

My other issue the CEL. I have cleared it many times it comes right back. I have even cleared the PCM by the steps i've seen here with the cable remove, headlights key trick. I have even cleaned the old one per the steps on this forum.my idle was stuck at about 1500 RPM. after cleaning it it got worse and idled about 2k I took the IAC back off and messed with the length a bit to achieve the 1200 is or so idle I have now.I have a P0505 IAC (AIS) Motor Circuits shorted I ordered a cheap $9 IAC off Ebay didn't change a thing So I deceided to order another. same results. I checked voltages and resistance from IAC plug to PCM plug. all Resistance checks in at 0.02 on all 4 colors. Key ON engine OFF my voltages read as follows: Grey w/red stripe 0 yellow/black stripe 1.34 brown/white stripe 0.01 purple/black stripe 0.56 Engine running: Grey/red 1.33 yellow/black 1.33 brown/white 0 purple/black 0.01 It doesn't appear to be working. However In my scanner I can Test the AIC and adjust the idle from 800 to 1300 RPM 1 step at a time. However I am getting 5 volts on the TPS sensor.. A few days ago anything with voltage switched from 0 to 1.34 0, 1.34, 0, 1.3 but this morning as I went to get EXACT numbers there was no switching. just constant voltage. I'm again wondering if swapping the starter I may have zapped the pcm.

 

[Tim_MN]

You cannot fix what you have not properly diagnosed. Throwing random parts at an unidentified problem will have a low success rate for solving the problem.

Fix the P0505 and the P1694. The P0700 can be ignored for now as it will likely clear up by itself when you fix the P1694. The CEL will return until the problems are fixed.

Cheap parts are cheap for a reason, always buy genuine Jeep engine sensors.

New parts do not automatically mean they are good parts, you always have to test both the sensor, and its wire circuit.

Most OBD-II trouble codes have a short list of probable causes. Keep in mind that if a sensor is failed, or if there is a wiring issue, the PCM can only tell you that it: 1) is not receiving any data, or 2) is not receiving the correct data. The PCM cannot figure out why 1 or 2 is happening, it just reports what is sees, or does not see. To trouble shoot you need to verify the function of the sensor, and verify the correct signals on the correct wires. Damaged wires, corrosion, blown fuses, open circuits, and short circuits can prevent sending/receiving of data, or can corrupt the data that is sent/received.

Always start the diagnostics and repairs with the lowest numbered trouble codes. Higher numbered trouble codes may be triggered by the lack of data, or by faulty data caused by the lower numbered faults.

 

[Automechnic077]

I understand throwing parts to fix something is a common dealer ritual with these XJs. I however can't afford that. I am just looking for help from you guys who have been around an XJ longer than myself.i have searched and tested everything that I can Google or find. From using the search feature.
so let's start with P0505.
I brought my multimeter out and test the 5v circuit loop. key on engine off.
I have 12.4 volts across the battery terminals.
TPS:
Wire closest to driver side "orange" 5.19 volts.
Center wire "orange blue" 4.34 volts
Other "brown yellow" Ground. 007 continuity.
All three tested to firewall strap.
Running back probe
Orange 5.21
Orange blue 0.88
Brown yellow 0.02

IAC:
Grey red 1.41
Yellow black 0
Brown white 0
Purple black 0
Engine running sensor connected back probing plug.
Gray red .56 volt avg it moves around a bit
Yellow black 0.03
Brown white 0.02
Purple black .56
Not sure where to go from here so I moved on.
I next unplugged the C1 connector from the pcm and check continuity from plug pins to IAC plug.
A10 0 00.3 ohms
A 11 0. 00.3 ohms
A 19 0. 00.3 ohms
A 20 0. 00.3 ohms
So no loss here everything seems kosher while jiggling wires as well.
The Map sensor also reads a fluctuating voltage on 2 leads from about 4.5 to 5.3.
I havent found any corrosion anywhere on any plugs or connectors . The wiring harness isn't hacked up I pulled out the ac controls. radio. Accessory panel. Removed dash panel from under steering wheel. Passenger side kick plate. Drivers kick plate rear hatch and behind spare tire everything looks kosher..
I read about a sweep test for the tps but don't know if that's necessary in this point.

 

[Automechnic077]

I tested the tps with my digital meter because it's all I have at the moment.
Idle 0.85
Wot 4.05

Also moving back to the ac issue I have C3 unplugged pin 23 (ac select input) key on engine off ac switch off I have 12.13 volts.
Pin 24 (brake lamp switch sense) I have 0 volts.
Hit brake pin 24 has 11.75 volts
Hit brake pin 23 has 12.02 volts

Key on engine off ac blower switch on 4 max ac brake off.
Pin 23 0.22 volts
Pin 24 0.02 volts
Key on engine off ac blower switch on 4 max ac brake on.
Pin 23 0.19
Pin 24 11.14

 

[Automechnic077]

I tested the tps with my digital meter because it's all I have at the moment.
Idle 0.85
Wot 4.05

Also moving back to the ac issue I have C3 unplugged
pin 23 (ac select input) key on engine off ac switch off I have 12.13 volts.
Pin 24 (brake lamp switch sense) I have 0 volts.
Hit brake pin 24 has 11.75 volts
Hit brake pin 23 has 12.02 volts

Key on engine off ac blower switch on 4 max ac brake off.
Pin 23 0.22 volts
Pin 24 0.02 volts
Key on engine off ac blower switch on 4 max ac brake on.
Pin 23 0.19
Pin 24 11.14

C3 connected key on engine off blower on
Both back probed
Pin 23 0.19
Pin 24 0.02

Engine on brake on ac on (compressor and fan on ice cold )
Both back probed at c3
Pin 23 0.25 volts
Pin 24 12.36

 

[Automechnic077]

I have run out of options and help. The thread has fallen to page 6. I'm just going to purchase a computer either from eBay or a local auto parts store.
Do I replace it with the exact same model number?

 

[Automechnic077]

I'm still fighting this issue. I haven't replaced the pcm. I however came across a new symptom / way to get the Jeep to act up and die. I noticed when switching through the fan speeds with the blower control in the OFF position switching the fan from 2 to 3 causes a change in the idle. IF I stop the switch between 2 and 3 the truck dies as always. Same bad behaviour just like it does when turning on the blower without my foot on the brake. I'm now pulling the harness apart under the hood hoping to find an answer before I rip to far into it.i started at the trans tube and workingy way towards the battery hoping to find chafing but everything look great

 

[Automechnic077]

I'm still fighting this issue. I haven't replaced the pcm. I however came across a new symptom / way to get the Jeep to act up and die. I noticed when switching through the fan speeds with the blower control in the OFF position switching the fan from 2 to 3 causes a change in the idle. IF I stop the switch between 2 and 3 the truck dies as always. Same bad behaviour just like it does when turning on the blower without my foot on the brake. I'm now pulling the harness apart under the hood hoping to find an answer before I rip to far into it.i started at the trans tube and workingy way towards the battery hoping to find chafing but everything look great

 

[Automechnic077]

Playing in the cab more with the ac fan switch has now caused the Jeep to only respond in position 4. Turning the key on in any other speed causes the fuel,airbag, belt, check gauges light to light then turn off. The oil pressure gauge goes from below 0 to 0 and the others all sit as far left as they go.no Movement. Again Jeep will start and run now in all these spots with the brake on. But now it won't run unless fan speed is on 4!
Had battery and alt tested both tested good.
Battery voltage 12.40
Battery running 14.7
Running ac on it drops over a volt and fluctuates until it dies.
Foot on brake ac on 14.1

 

[McQue]

Only fan speed 4 (HI) working means your blower motor resistor is open. Position 4 bypasses the resistor and puts ground (g108) on you blower motor relay and the blower runs at the highest speed. The brake pedal interaction seems to me that there is some sort of short or open circuit. There is a splice s207 for the g108 ground in the lower instrument panel trough. Inspect all the wiring in this area.

 

[Automechnic077]

Thanks for the reply I still have most of the dash apart I will check on it tomorrow when the sun comes up. I did take the Blower resistor out, and the relay above it both causing a no start. Unplugging the Plug from the ac controls also causes no start. I swear Jeep has the funniest wiring! Perhaps I didn't plug the resistor in snugly as it has the weird safety plug on it. OR it burnt up?

I have also followed the steps in this thread as well. http://www.naxja.org/forum/showthread.php?t=1119312 His resolve appeared to be a PCM. I wont be able to get one locally and will have to resort to Ebay. $180.00 and tempted to throw it at the problem and hope for the best! This all started when the starter ground to the frame.

 

[Automechnic077]

Ok, I have inspected wiggled jiggled every wire under the dash I also added a extra ground to g108 because it is just screwed to the dash mount.. I grounded it to the bolt near the hood release with #10 wire. Being 300 lbs I had to take the seat out to get in there and look! What a bear.
The blower resistor is/was plugged in this whole time. Nothing in that area looks like it overheated.
Like I said above turning the key to run the dash only responds with fan switch in position 4. Mode switch OFF this is also the only time the fuel pump primes. Turn key to run position. In 1,2,3 fan speed or any mode the dash sits dead the only thing I can hear is the tape deck in the radio click turning the key on and off. The black relay near the green plug behind the glovebox also clicks as I felt it with my hand.
I took the ac controls apart everything looked kosher inside there, grease good as new.
Now what