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  #31  
Old February 23rd, 2018, 18:01
soyjer soyjer is offline
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Re: 1999 XJ - when is cruise control light SUPPOSED to light?

Removed the airbag, and the green speed control switch connector was hanging loose, waiting for a cruise control enabled clock spring to be installed. Someone must have replaced the clock spring on this otherwise cruise control enabled vehicle, and maybe they were in a hurry because they installed a non cruise control clock spring instead of a cruise control enabled clock spring. The only obvious difference is that the non cruise control clock spring does not have a connector to connect to the existing green switch connector.
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  #32  
Old February 23rd, 2018, 18:44
smccollamjr smccollamjr is offline
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1999 XJ - when is cruise control light SUPPOSED to light?

Glad you got to the bottom of it.


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  #33  
Old February 24th, 2018, 18:27
soyjer soyjer is offline
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Re: 1999 XJ - when is cruise control light SUPPOSED to light?

Removed the steering wheel and got a closer look at the Crown Automotive Clockspring (w/o cruise control) connector that does not have a speed control two wire connector attached to it...and sure enough, the pins for speed control are there, Crown just doesn't hook up the two wires and little green connector to it unless it is being sold as cruise control enabled. I don't think the pin out for that connector is publicly documented by Crown, but if one assumes that pin 1 is on the left and pin 6 is on the right, pin 2 is sensor ground and pin 3 is speed control switch signal.

I was able to connect to those two pins to complete the circuit over to the big green speed control connector attached to the steering wheel switches, but I wouldn't necessarily recommend this, because when you are working around airbag circuitry you would have to be extremely careful to not interfere with that circuitry in any way, and in order to connect to those pins you have to remove some plastic and work in very tiny and tight spaces, and you have to connect to those pins without interfering with the airbag pins. Because the airbag is connected to the far right end of the 6 pin connector, and I was only working on pins 2 and 3, and because I have a background in electronics repair, I felt confident to tackle the project, but if there is any doubt in your mind that you can't do it without interfering with the airbag circuitry, then don't try, of course. You can find Crown's cruise control enabled version of that clock spring for about $90 online.
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  #34  
Old February 25th, 2018, 10:10
soyjer soyjer is offline
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Re: 1999 XJ - when is cruise control light SUPPOSED to light?

I measured my speed control switches' resistances when completely disconnected from the system, and these were the results:

The values shown in the chart below are accurate for at least my 1999 Jeep Cherokee XJ using my DVM, and I suspect that they are close to the correct values for any Jeep XJ or Wrangler from 1999 through 2001.
as I mentioned in a previous post, at least some of the resistance's can be up to 25% off the correct values and still function properly, because the PCM merely needs for the resistances to be within ranges that allow the PCM to distinguish between one button push and another button push:

1999-2001
None-----20.3K
On----------472
Set--------4.32K
Res-------8.77K
Coast----2.58K
Cancel--1.17K

And here are the values measured by the other guy in the other post (I think that his measurements were made with the PCM still connected up to the switches):


-------------1998------1999-2001
None------Open ------19K
On----------920-----------440
Set--------6.6K----------4.1K
Res------15K------------8.35K
Coast-----3K------------2.5K
Cancel----0K-----------1.15K
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  #35  
Old February 25th, 2018, 11:53
soyjer soyjer is offline
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Re: 1999 XJ - when is cruise control light SUPPOSED to light?

Actually, the other guy must have made his measurements with the switches unhooked from the PCM just like I did, because I just rechecked the resistance values with the PCM connected, and they are all substantially different from what they were disconnected.
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  #36  
Old February 25th, 2018, 12:16
smccollamjr smccollamjr is offline
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1999 XJ - when is cruise control light SUPPOSED to light?

The ones I made were with the switches disconnected from the PCM.


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  #37  
Old March 27th, 2018, 19:42
soyjer soyjer is offline
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Re: 1999 XJ - when is cruise control light SUPPOSED to light?

After testing this cruise control system for weeks now under all different conditions, I am now almost convinced that in addition to my original problem of the wrong clock spring being installed into this vehicle, the PCM must have something wrong with its cruise control functioning, because my cruise control light either comes on or doesn't or stays on or doesn't at so far seeming totally random times. The only thing that I found consistently true about the system is that if I shut the engine off and then restart the engine then the cruise control light will come on at least one time. But one day I'll go 50 feet and it will shut off until I restart the engine and another day I can drive out on bumpy roads for an hour and the light stays on the whole time.

What I have learned is that the position of the brake pedal is irrelevant to whether the CRUISE light will come on or not, and that although the servo electrical connector has to connect the servo to the PCM (other than the speed control power supply that does not need to be supplied to the servo because if you press on the brake pedal it interrupts that), there does not have to be any vacuum applied to the servo for the CRUISE light to come on.

The problem with trying to troubleshoot the speed control system is that I have no way of knowing what OTHER conditions the PCM requires before it will decide that it's okay to turn the CRUISE light on. Does it require the VSS sensor to be connected to the PCM before it will allow the CRUISE light to come on? If so, then that's another circuit that could be intermittent and causing my CRUISE light to intermittently not work.

It seems as if you almost have to have the actual PCM software computer code to analyze in order to try to figure out what the programmer was thinking when he/she wrote the software. If I really need reliable cruise control I guess my only options would be to either replace the PCM and hope that the intermittent problem is internal to the PCM, or just start replacing every sensor circuit on the vehicle until I find the one that is providing an intermittent signal to the PCM.

There must be a software flowchart at a dealership or somewhere that would give me some clue as to what the PCM requires before it will allow that CRUISE control light to come on, but I doubt I would ever be able to find such a thing. But I doubt I would ever be able to find such a thing.
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  #38  
Old March 28th, 2018, 20:58
soyjer soyjer is offline
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Re: 1999 XJ - when is cruise control light SUPPOSED to light?

SOLVED!...or at least I've determined one cause of the seemingly random intermittent problem of not being able to get the CRUISE lamp on the dash to light up reliably. I'm assuming that this only applies to Jeeps with the cruise control switch set that disconnected measures ~ 19.5 K ohms (instead of infinite ohms open circuit like the 1998 Jeep Cherokee XJ) when no buttons are pushed (I know that it applies to my 1999 Jeep Cherokee XJ, and assume that it also applies to the 2000 & 2001 XJ's):

If the circuit going from the speed control switches on the steering wheel through the clock spring to the PCM becomes open for at least ~ 3 seconds (and the three seconds can be either a straight uninterrupted 3 seconds or a number of shorter open circuits that add up to a total of more than ~ 3 seconds), the PCM then completely shuts down the speed control function, including any ability to turn on the CRUISE light on the dash, and the only remedy for this situation is to then shut off the engine, wait about 10 seconds, and then restart the engine. It doesn't matter whether the CRUISE lamp was on or off when the ~ 3-second open circuit occurs, either way the PCM will shut down the speed control function, until the engine is restarted as stated above.

Because of the above, while you are trying to fix an intermittent problem with getting your CRUISE lamp to come on, you can have a vehicle that, other than the above "history of open circuit conditions totalling > ~ 3 seconds" contained inside of the PCM, is functionally perfect in every way...including an otherwise perfectly functioning cruise control system...and yet will refuse to turn on the cruise lamp until you restart the vehicle which basically erases the "history of open circuit conditions totalling > ~ 3 seconds" contained inside of the PCM.

But if you know about the above, then you will know that when the speed control switch circuitry seems fully connected to the PCM, and yet the CRUISE lamp still refuses to come on more than ONCE after you start the engine, it may be because the PCM has recorded a "history of open circuit conditions totalling > ~ 3 seconds" since the last time that the engine was started. And because the open circuit condition does not have to be for a sustained 3 seconds...the three seconds could be the total of several or many very brief open circuit conditions...those open circuit conditions may each be for such a brief time that they are not even noticeable by a monitoring voltmeter. So you may have an intermittent open circuit condition in your speed control switch to PCM circuitry that cannot be detected using a regular digital or analog voltmeter or ohmmeter, where your only easily obtainable evidence that it may be an intermittent open circuit problem would be the CRUISE lamp behavior described above. If your CRUISE lamp is exhibiting the behavior described above, and you want to verify that there is an intermittent open circuit condition occurring, and determine which part of the circuitry is the problem, and you've already done all the normal ohm checks to make sure that the circuitry seems okay, then the next step would be to try bypassing or replacing each section of the circuitry, one at a time.
Just be very careful when working around the clock spring and speed control switches, because the airbag circuitry runs through the same clock spring.


BTW, even though I described the PCM's shutting down of the cruise control system as the PCM containing a "history of open circuit conditions totalling > ~ 3 seconds", that is just a convenient way for me to describe what the PCM does as far as the effect it has. I have no idea electrically what is going on inside of the PCM that causes it to behave this way... It could be actually in the software programming (by design or by accident), or it may be just the PCM's electrical circuitry reacting electronically to open circuit conditions on the PCM's speed signal pin where it is expecting approximately 19.5 K ohms. But as long as we know what the behavior is, knowing exactly what is going on INSIDE of the PCM is not necessary.
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  #39  
Old March 29th, 2018, 08:39
smccollamjr smccollamjr is offline
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1999 XJ - when is cruise control light SUPPOSED to light?

What’s causing your open circuit?
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  #40  
Old March 29th, 2018, 10:10
soyjer soyjer is offline
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Re: 1999 XJ - when is cruise control light SUPPOSED to light?

Well, mine is a special case, because I had to make my system work with a non cruise control clock spring, AND I didn't want to alter the existing green connector coming from my good steering wheel switches, and so I had to modify two solderless push on connectors to try to get them to slip tightly over the two pins on that green connector, and I think that I just did a crappy job of it the first time around, which allowed them to rattle around and make very brief disconnections in the circuit at random times, and as soon as the total open circuit time added up to greater than 3 seconds, the PCM then decided that it wasn't going to allow me to turn on the CRUISE light again until I restarted the engine.

And of course with me previously not knowing about this PCM behavior, I was monitoring the voltage on the speed control signal pin of the PCM while I was driving the vehicle, and I couldn't figure out why the cruise control was behaving like it was when the monitored voltage always seemed exactly perfect. The correct voltage for that pin, when the 19.5K ohm switches are connected, is about 4.7 volts with no buttons pushed, and a little over 5 volts open circuit (with no 19.5K ohm present). But I would have needed a recording oscilloscope or something like that to have been able to see the brief voltage changes that were occurring without my knowledge. It never occurred to me that the PCM would for some reason add up the total of all brief open circuit conditions and then shut down the system once it had collected 3 seconds worth of them. I'm relatively new to computer managed vehicles, and so I'm not used to a vehicle failing due to something that happened in the past and is not currently happening anymore. What's next?... The PCM deciding that I've had too many flat tires this year and so it shuts down the vehicle until I get new tires? 😚

Until I have driven the vehicle for a month or so after improving my green connector connections, I won't be able to actually say with 100% certainty what was causing my intermittent open circuit conditions, and in fact I can't even say that that was my problem with 100% certainty, because it is also remotely possible that there is some other sensor or condition that is not satisfying the PCM and causing it to do similar behavior.

But regardless of what the situation is with my particular vehicle, everything I have said about this PCM behavior is true, because I created resistances to stimulate the 19.5 k with no buttons pushed and 440 ohms with the cruise control on off button momentarily pressed, and connected them in place of the existing steering wheel switches, and was able to repeatedly get the PCM to exhibit the behavior that I described. Whenever I disconnected the 19.5 K ohm fixed resistance for a total time of greater than 3 seconds, no matter how brief the interruptions or how many, and no matter whether the cruise light was on or off while I was doing this, the PCM would exhibit the behavior and I would have to restart the engine to get the PCM to allow the cruise light to come on.

I will report back in a week and a month how my vehicle is doing, but in the meantime at least now it's recorded how the PCM behaves, so that people won't pull their hair out trying to figure out why a system that tests absolutely perfectly still won't work right because the PCM has decided that there has been greater than three seconds worth of open circuit conditions since the last engine start and so the PCM then shuts down the system until you restart it.

My OBD2 reader did not read any error codes during this whole process, but I can't say with 100% certainty that there is no code for "speed control signal - (history of) open circuit conditions"...if so, that might have saved me some time on this project.

I will recreate the problem and then check with my code reader to verify that there is no code generated, or there is.
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