Cherokee ECM problems.

[tatuedrednek]

Hey all! Thought I would post this up here and see if I can find some more advice. I have a 96 cherokee that has had a check engine light since I bought it. I have spent the last four months fixing everything that is remotely wrong with it, ie. leaks, etc. The time has come to diagnose my MIL, problem is, I can't get ANY scanner to communicate with the ecm. And to save my time and yours, I am a professional auto tech and am pretty sure I have covered all my bases. This thing has me stumped. All wiring from the ecm to the aldl (datalink connector) has good continuity, with the exception of one wire. I found the open in the circuit and repaired it. My ecm has all the proper powers, grounds, 5v references, etc. Even tried a new ecm to no avail. Did a bunch of research on the problem and all I find is problems with a sensor shorting out and causing this issue, but also causing a no start. My rig runs and drives just fine. Tested all 5v references to all sensors, no problems there. I can't be the only guy that has had this happen. If anyone has any ideas let me know thanks!

 

[Desert Dan]

It sounds like you know what you are doing.

Have you checked these?

Oxygen sensor on exhaust manifold?

Gas Cap?

Catalytic Converter?


If it runs fine put tape over the light? LOL

 

[tatuedrednek]

HAHAHAHAHAHAHAHA!!!!!!!!! Thank Dan! Apparently great minds think alike! I have had tape over it while I worked on everything else! And on a more serious note, all of your suggested items are AOK.

 

[baca327]

First of all are you using a star scan, drb (chrysler scanners) or just a generic scanner? Your issue might lie in your equipment your using to diagnose. Is it not communicating with the PCM or is it just saying there are no active codes? Could be TCM related if your using a generic scanner, also make sure your getting power at the obd2 port if its not communicating. Also inspect the actual obd2 port under the dash.

 

[tatuedrednek]

I have used multiple different brands and makes of scanners. Does not make a difference. Also, as I said earlier, no communication. I have power at the datalink connector (OBD2 connector), otherwise the scanner would not power up. Not trying to be a jerk, just want to make it clear that I have checked absolutely everything I can think of. Any advice, however, is greatly appreciated. I know I never get frustrated and overlook things!

 

[bulfo4]

Hey, we're having almost the same type of problem right now also on a 1996 Cherokee. We put a 4.6L stroker into it, and it cranks and cranks but takes forever to start, and dies at low idle. We're not mechanics, but we swapped and checked about everything and kind of came down to it being the PCM. On ours, the scanner (cheapo from harbor freight) has power, but can't connect. Giving in, we limped it to a shop and apparently their reader briefly said cam sensor, but then they said the PCM was dead or died and we had to tow it home (nothing worse than driving it there and towing it home). They said the PCM wasn't grounded correctly at some point, and were going to jumper from the outside of the PCM box to the engine compartment. Didn't fix it.

Probably not any help, but we're curious if you get an answer. Good luck!

 

[monk]

1997 TJ here. Purchased in 1996 the CEL has been on more than off, Recently I discovered that I can run the OBD and have the diagnostic codes displayed in the digital odometer display. More here...

http://www.offroaders.com/tech/jeep/TJ_diagnostic_codes.htm

Not sure if this applies to your car but it has helped me solve multiple problems. Just replaced the upstream o2 sensor this week per a code 21 and the car runs much better.

Good luck
Monk

 

[old_man]

Take a trip over to www.naxja.org. It is the largest tech site for Jeep Cherokee's in the world.

 

[tatuedrednek]

bulfo, if you have a bad cam snesor that is shorted internally it will cause the ecm to "go to sleep". Try unplugging the cam sensor and scanning it. Crank sensor, tps, vss that are shorted will also cause the same problem.

old man, Thanks for the tip! I'll give it a shot!

monk, sadly my xj is the last year of analog dash. Cool trick though!

And thank you all for your input!

 

[bulfo4]

Monk- thanks for the tip on the lights. We'll give that a try.

Old man - naxja is great! Lots of good info. One of a number of forums we look to for good info.

Tatuedrednek - good idea on how to try to rule out sensors giving issue to scanning. Thanks!

 

[baca327]

I have used multiple different brands and makes of scanners. Does not make a difference. Also, as I said earlier, no communication. I have power at the datalink connector (OBD2 connector), otherwise the scanner would not power up. Not trying to be a jerk, just want to make it clear that I have checked absolutely everything I can think of. Any advice, however, is greatly appreciated. I know I never get frustrated and overlook things!

The DRB III is a chrysler specific scanner that can test PCI BUS and individual modules, which seems is what you are in need of. A generic scanner doesn't offer nearly the options. Other than that I would start looking through trouble trees.

 

[tatuedrednek]

Thanks for the info. I'll give that a shot.

 

[BIGdaddy]

pull the light bulb


EDIT: Kidding aside, are we sure this isn't an OBDI system? My 1992 is an OBDI and all I have to do is flick the ignition on and off 3 times, leaving it on the last time, and at that point the check engine light itself will flash numeric codes that correlate to a glossary that I have printed out.

We sure that this rig doesn't have that type of setup?

Might be an obvious, "Nope, it's OBDII", but 1996 is notoriously a crossover year for a lot of other things drivetrain/body wise, so I thought there might be a chance...

 

[tatuedrednek]

It's OBDII, which I was pleasantly suprised to find. Jeep products are notoriously hard to diagnose with an OBDI system!

 

[BIGdaddy]

It's OBDII, which I was pleasantly suprised to find. Jeep products are notoriously hard to diagnose with an OBDI system!

That hasn't been the case with my cherokee. It's actually been very easy to pinpoint issues so far...

Have you tried the method I described to pull codes from your computer?

Might be worth a try since nothing else seems to be working.