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Code scanner does not read my Jeep, No + to coils, Jeep died on the HW. PCM or CPS?

Plays For Jeeps

NAXJA Forum User
Location
Allentown PA
Since my Jeep will not scan with a code scanner I am leding towards a PCM. Only problem is that I do not know how to match my PCM to a used one from the junkyard. What do I need to look for in a used PCM?

I called the dealership and they told me that PCM's do not need to be reflashed, I just need to get the proper one.

Problem is that there are over 22 differnt PCM versions!
 
Re: Code scanner does not read my Jeep, No + to coils, Jeep died on the HW. PCM or CPS?

It would really help if you told us what model year you have.

Look at the PCM that's in your truck now and see if there's a sticker on it somewhere - copy all the numbers down (or take a picture of it) and show that to the parts guy at the dealership.

Rob
 
Re: Code scanner does not read my Jeep, No + to coils, Jeep died on the HW. PCM or CPS?

get the same year, same engine, similar optioned vehcile.

that's a PCM issue...the reader isn't reading because you're PCM is most likely fried.
 
Re: Code scanner does not read my Jeep, No + to coils, Jeep died on the HW. PCM or CPS?

Sorry guys. Its a 96 4 door Auto SE.

The same thing happened a month ago and it just fixed itself. Then yesterday it happened again.
 
Re: Code scanner does not read my Jeep, No + to coils, Jeep died on the HW. PCM or CPS?

What is it doing? PCM's are rarely the bad part.
 
Re: Code scanner does not read my Jeep, No + to coils, Jeep died on the HW. PCM or CPS?

96? You can still do the "Key On...off...on...off...on...wait" code read on that. Don't go "on" to start it, but the last click prior to that. You'll get a series of two-digit codes flashed through the Check Engine light, but be patient.

Post back any results. Unless you've truly fried the PCM, of course.

Jim www.yuccaman.com
 
Re: Code scanner does not read my Jeep, No + to coils, Jeep died on the HW. PCM or CPS?

Could be your crank sensor.

OBD2 should be easily read by a code scanner, though; your 96 has OBD2.

However, I cannot get my OBD1 to transmit to a scanner. I'm not alone on that problem though, I at least know of one other person on these forums that's tried with no luck.
 
Re: Code scanner does not read my Jeep, No + to coils, Jeep died on the HW. PCM or CPS?

Blaine B. said:
Could be your crank sensor.

OBD2 should be easily read by a code scanner, though; your 96 has OBD2.

However, I cannot get my OBD1 to transmit to a scanner. I'm not alone on that problem though, I at least know of one other person on these forums that's tried with no luck.

The PCM must get a signal from the CPS before anything else happens.Wifes 98 died at her work,no fuel pressure,I thought pump died,towed it to Mech,they could not pull any codes- with scanner-the check engine light wouldn,t even come on, Final outcome-replaced the CPS and everything was back to normal.

Wayne
 
old_man said:
What is it doing? PCM's are rarely the bad part.

Agreed, but sometimes they are.

I just had to have mine replaced - it was exhibiting the signs of a CPS failure, but I was also getting no Check Engine or Maint Reqd light. A new CPS didn't solve the problem (though the old one was shot), so we had to go for a new PCM. That did solve it.

Not saying it's the case for the O/P, but just that it CAN happen that a PCM fails.
 
Re: Code scanner does not read my Jeep, No + to coils, Jeep died on the HW. PCM or CPS?

Mine had similar symptoms a couple months ago. No spark, no fuel, no communication with code reader. Changed cps, got spark, changed pcm, got fuel and communication back. Wierd
 
Re: Code scanner does not read my Jeep, No + to coils, Jeep died on the HW. PCM or CPS?

well my xj did this about a month ago but after work. It would crank and crank but not start. I had fuel and when I had it towed all the mechanic did was unplug random sensors and plugged them back in and she fired up.

Fast forward to 2 days ago. On my way to an interview, coming around a turn and the jeep just died. RPM's dropped, power cut and power steering went out. Then on the side of the road she would crank and crank with no start.
 
Re: Code scanner does not read my Jeep, No + to coils, Jeep died on the HW. PCM or CPS?

intermittent problems... sounds a lot like CPS. mine died, started a few hours later... then died two days later and left me stranded at work. replaced the CPS with one from pep boys (closest I could find) and it's been working fine since. :) nothing on the OBD2 reader, nothing with the "on off, on off" trick, no spark, no fuel, but plenty of power for the starter, gauge cluster lights up but fuel and voltage don't register, key left in "On" position will show "No Bus" in the odometer, all relays and fuses are good.
 
Plays For Jeeps said:
well my xj did this about a month ago but after work. It would crank and crank but not start. I had fuel and when I had it towed all the mechanic did was unplug random sensors and plugged them back in and she fired up.

Fast forward to 2 days ago. On my way to an interview, coming around a turn and the jeep just died. RPM's dropped, power cut and power steering went out. Then on the side of the road she would crank and crank with no start.
The first part sounds a lot like a CPS failure. If the CPS isn't right, it can even prevent the computer from powering up (in my case, when the CPS died, it did so in such a fashion that seemed to have killed something inside the computer when it went, since the ultimate solution to my issue was a new CPS and PCM).

The second part sounds like something shifted and caused either a short or open in the CPS wiring. As I understand it, the CPS is the only source of information the computer has for timing; you can't run the engine without it, so I can see why it would cut out if the PCM lost signal from the PCM.

If a new CPS doesn't do the trick, you may be stuck in computerland.

Good luck.

Rob
 
Since my Jeep will not scan with a code scanner I am leding towards a PCM. Only problem is that I do not know how to match my PCM to a used one from the junkyard. What do I need to look for in a used PCM?

I called the dealership and they told me that PCM's do not need to be reflashed, I just need to get the proper one.

Problem is that there are over 22 differnt PCM versions!

I know this is an old thread, but i was wondering what the final outcome was for " Plays for Jeeps"?
Because i am having the exact same issues.
cant pull any code by ether method no check engine light, no communication with scanner,no power to coil or enjectors. The odd thing is the guages seem to be working fine
 
What have you tried so far? The crankshaft position sensor is the most likely problem as stated above.
 
I could never get an OBD-1 scanner to read my 95 XJ, I have heard others having difficulty with the OBD-1 system as well, even though there is that nice little plug there between the airbox and brake master cylinder which is exactly for this purpose...
 
After reading your post, I take it that the scanner doesn't even communicate with the ECU, correct?

If that is the case, it isn't a sensor or the like, it means that the ECU has a problem. Having said that, the problem could be that it simply isn't getting power. I would double check all the fuses and if you don't find any bad, I would get a voltmeter and actually check for 12v at the ECU and that the ground is actually good. If those voltages are correct, you may indeed have a bad ECU, but ECU failures are very uncommon.

Since my Jeep will not scan with a code scanner I am leding towards a PCM. Only problem is that I do not know how to match my PCM to a used one from the junkyard. What do I need to look for in a used PCM?

I called the dealership and they told me that PCM's do not need to be reflashed, I just need to get the proper one.

Problem is that there are over 22 differnt PCM versions!
 
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