Jeep Cherokee:

Cranks but will not start, no PCM function.

You are not logged in.

#1 9/1/2011 5:41 PM

bob gerber
New member
Registered: 9/1/2011
Posts: 3

Cranks but will not start, no PCM function.

I have a 1996 Jeep Cherokee sport. I have no communication to the computer with a scanner, no check engine light, no 5 v reference, no spark.  I have tried to manually pull codes with the key.  The dealer says that it does not have an immobilizer by the VIN number.  I have power and grounds to the PCM connectors.  The ASD relay has power , but does not turn on. I have tried a used, and a re-manufactured PCM with the same results. I do not have a security light on. The engine cranks fine.  I have tried locking and unlocking all the doors.  It ran good, was shut off and did this.  I have run out of ideas.

Jeep Cherokee Recalls, TSBs and Service Information >> ALLDATA

Offline

 
Sponsored Links
ALLDATAdiy.com

The Leading Source of Professional Diagnostic and Repair Information.

#2 9/1/2011 9:40 PM

TechHelp2
Administrator
Registered: 11/24/2009
Posts: 1298

Re: Cranks but will not start, no PCM function.

You have done some good checks but it is time to go to basics.

Did you check all of the fuses? Check the Maxi fuses too.

Did you check for spark?

Did you check for injector pulse?

Did you check for fuel pressure?

These are the basic checks that need to be done. From what it sounds like you probably did these procedures already. I just need to know if you did them so I can help you better.

You said you had current to the ASD relay but does not turn on. Below is the operation of the ASD circuit. It is possible the ground to the relay is bad or the relay itself is bad. Try to swap the relay with a known good one. The description of the circuit is below.

CIRCUIT OPERATION:

When the ignition switch is in either the START or RUN position, it connects circuit A1 from fuse 8 in the Power Distribution Center (PDC) to circuit A21. Circuit A21 powers circuit F99 through PDC fuse 18. Circuit F99 feeds the coil side of the Automatic Shut Down (ASD) relay. The Power train Control Module (PCM) provides ground for the relay on circuit K900. Circuit K900 connects to cavity C3 of the PCM.

When the PCM grounds the ASD relay, contacts inside the relay close and connect circuit F5 from fuse 20 in the PDC to circuit A142. Circuit A142 splices to the generator field terminal, fuel injectors, ignition coil and the upstream and downstream heated oxygen sensors. Circuit A142 also connects to cavity C12 of the PCM.

I read an article on this problem and one common fix was if the fuse or fuses are blown and you have all the above problems happening, go to the crank sensor and disconnect it to see if all of the problems go away. I read that the crank sensor shorts out and causes this problem on a lot of these jeeps. This could be causing your problem. It doesn't hurt to check it out.

I hope this helps. If you need more assistance get back to us and we will look into the no start condition further.


realworldautomotive.com
car and truck information like nowhere else
Jeep Cherokee Recalls, TSBs and Service Information >> ALLDATA

Offline

 

#3 9/1/2011 10:44 PM

bob gerber
New member
Registered: 9/1/2011
Posts: 3

Re: Cranks but will not start, no PCM function.

The fuses are all good, no spark or injector pulse. I have no fuel pressure. I do not hear the fuel pump run. I did unplug the map, TPS, crank and cam sensors, I forgot about the O2, will try that next.

Jeep Cherokee Recalls, TSBs and Service Information >> ALLDATA

Offline

 

#4 9/2/2011 3:42 AM

TechHelp2
Administrator
Registered: 11/24/2009
Posts: 1298

Re: Cranks but will not start, no PCM function.

You still don't have spark or injector pulse; this should be looked into first. It still could be a bad crank sensor. The crank sensor sends the pulse to the PCM and then it sends the signals to the proper areas like spark, fuel relay, and injector pulse.

The next thing would be to find out why you don't have any fuel pressure. Then go on from there. We are here to help when you need it.


realworldautomotive.com
car and truck information like nowhere else
Jeep Cherokee Recalls, TSBs and Service Information >> ALLDATA

Offline

 

#5 9/2/2011 4:39 AM

bob gerber
New member
Registered: 9/1/2011
Posts: 3

Re: Cranks but will not start, no PCM function.

I unplugged all of the sensors one at a time. It still acts like the PCM is offline.  I do not have a 5 volt reference pulse or a service engine light.

Jeep Cherokee Recalls, TSBs and Service Information >> ALLDATA

Offline

 

#6 9/2/2011 2:57 PM

TechHelp2
Administrator
Registered: 11/24/2009
Posts: 1298

Re: Cranks but will not start, no PCM function.

Did you check all the fuses on both fuse panels?

There are two fuse distribution panels; one is next to the battery.

The other one is behind the right side kick panel on the passenger side.

Two things are happening either you are missing a fuse or you have two PCM's that are bad. You said you plugged in another one, was it a known good one?

Can you plug in your PCM into another jeep to see if it is functioning ok?

On the ASD relay you said you have power but it won't turn on.

Can you ground the terminal of the relay for ground and see if you can activate the relay. If you can does the engine start now. If you can get the engine to start then you would seem to have a ground problem on the ASD relay circuit. This is just a guess. The ASD relay supplies voltage to all of the components needed to run the engine.

Let me know how you make out, I'll continue to research this problem.


realworldautomotive.com
car and truck information like nowhere else
Jeep Cherokee Recalls, TSBs and Service Information >> ALLDATA

Offline

 

#7 9/4/2011 6:00 PM

Administrator
Administrator
Registered: 9/27/2008
Posts: 1279

Re: Cranks but will not start, no PCM function.

Man, from what I've read so far, I'd be making a B-Line to the right/rear of the engine where G106, G107 & G108 are bolted together.

G107 supplies the 2 main grounds to the PCM at terminals A31 & A32. If G107 looks good, make sure the ground is reaching A31/A32 (no open circuits).


realworldautomotive.com
car and truck information like nowhere else
Jeep Cherokee Recalls, TSBs and Service Information >> ALLDATA

Offline

 

#8 2/21/2012 7:15 PM

MrkaFaca
New member
Registered: 2/21/2012
Posts: 1

Re: Cranks but will not start, no PCM function.

Hi to all,

It seems that I have the similar problem with my Jeep Cherokee. In the first case, I get in my car, turned the key, my car cranks and the engine starts. For example, I drive a half an hour or one hour, then I turn off the car. After few minutes when I try to start, my car cranks normal but, engine will not start. I can try cranking many times and my car cranks but engine still won't start. Second case - I leave car for several hours. After that time, I get in my car again, turned the key, car cranks and engine start immediately. Although, in my country it is a heavy winter now, I started to wonder if the problem is connected to the coldness, or maybe water somewhere in the engine? During the summer I haven't  had any problem like this. Whether it might be associated with that the engine will not start because  of the warmth? Sounds like as if the car needs to cool down, that car turned again? Does anyone have an idea?
Thanks in advance!

Jeep Cherokee Recalls, TSBs and Service Information >> ALLDATA

Offline

 

#9 2/22/2012 5:23 AM

TechHelp2
Administrator
Registered: 11/24/2009
Posts: 1298

Re: Cranks but will not start, no PCM function.

When the car won't start you first need to find out what area the problem is in, whether it is in the fuel system or the ignition system. 

The first thing to check when the engine won't start is to see if you have spark at the spark plugs. When the car won't start and you have a spark at the spark plugs then the problem would most likely be in the fuel system.

Checking fuel pressure would be next and also checking to see if you have an injector pulse at the fuel injectors. This can be checked by a simple tool called a noid light. You just unplug an injector and put the noid light in the fuel injector plug. When you crank the engine over and the noid light flashes then you have injector pulse.You would then need to check the fuel pressure next.


realworldautomotive.com
car and truck information like nowhere else
Jeep Cherokee Recalls, TSBs and Service Information >> ALLDATA

Offline

 

#10 1/19/2015 8:46 AM

busman
New member
Registered: 1/19/2015
Posts: 1

Re: Cranks but will not start, no PCM function.

I have a 2000 Cherokee Sport with a similar problem.  Yesterday it was running fine, today it will crank but no start.  I noticed a couple things; first it says "no bus" on the display, 2nd, I cannot hear the fuel pump run (which is normally audible), 3rd, I cannot communicate with the OBD II scanner (which I normally can).  I've done some preliminary checks of the fuses, but need to check the ASD relay circuit.  I've been trying to locate a wire diagram for this series Jeep, but I'm not having much luck.  Any thoughts?  I have read the other threads about the crank sensor, so I'll check that it's not open (what should the OHM reading be?)  The O2 sensor was replaced last year, but that didn't affect the starting (just check engine light and code).  Thanks for you help in advance.
Aaron

Jeep Cherokee Recalls, TSBs and Service Information >> ALLDATA

Offline

 
E-mail Page
Print Page
Save or Share Information
ALLDATAdiy.com is the leading source of factory diagnostic & repair information specific to your car.

Powered by PunBB
Copyright © 2007-  RealWorldAutomotive.com

Save or Share Automotive Information
Custom Search