Help. Stranded and Late for Work.

[Sidewinder CC]

Update:

Got the Jeep into the shop and started testing.

I have no spark and no fuel, although the fuel rail is pressurized.

Fuses are good and power at ASD and fuel pump relay checked with test light (ruling out ignition switch).

I have NO 5 volt reference on the shared signal line.

I've pulled the IAC, MAP, TPS, VSS, EVAP purge solenoid, low pressure AC cut switch, cam position sensor, crank position sensor and NO 5 volts.....just trace voltage.

I have battery voltage and a good ground to the PCM. The PCM still gets warm to the touch near connector A anytime the battery is connected.

So, it would seem to me that I have a bad PCM here. I don't want to replace it however just to have it blow again because I have a short somewhere. Should I do additional testing on all the sensors to make sure I don't have a short somewhere that could render a 2nd PCM a paperweight.

I put the door lock fuse back in and they cycled once and stopped. I hit the switch and they all worked. I removed the fuse again. So, my theory as it sits goes 2 ways.....

1. I had a short to power in the door lock circuit which drug down the battery. When I jumped it, either do to age just dumb luck the PCM fried.

2. The PCM shorted internally initially, dragging the battery down confusing the door lock module with questionable voltage.

Thoughts?

What do you mean "Shared Signal Line"?

You shouldn't have a 5 volt reference on a shared signal circuit.

Look for 5 volts at least one sensor at the pin cavity with the Orange wire. The 5 volt reference originates at pin A17 of PCM connector C1 (Black) then is spliced, like a spider web, to all other sensors using 5 volts.

 

[98NWCherokee]

Sorry, I'm still learning and my terminology may be a bit off. I was referring to the 5 volt power feed (orange wire), not the signal wire.

I do not have 5 volts at the orange 5 volt wire at any of the sensors I listed above. I also hooked into one with a t-pin and watched my meter as I disconnected each sensor. I don't believe the PCM is providing the 5 volts.

I did check A17 and I only have trace voltage.

 

[Sidewinder CC]

Sorry, I'm still learning and my terminology may be a bit off. I was referring to the 5 volt power feed (orange wire), not the signal wire.

I do not have 5 volts at the orange 5 volt wire at any of the sensors I listed above. I also hooked into one with a t-pin and watched my meter as I disconnected each sensor. I don't believe the PCM is providing the 5 volts.

I did check A17 and I only have trace voltage.

Did you back probe A17?

Here's C1 that was used for another problem but you can see A17.

Anyway, if you pull C1 off and examine all the pins and cavities for defects and they look good, and you check resistance of A17 wire to any sensor Organge wire and continuity is read, I'd say the PCM is toast.

 

[98NWCherokee]

Any idea on prices? Please don't tell me this should be a dealer only replacement like the CPS? My local dealership wants $699 and $112.50 to flash and it would be a week out.

 

[McQue]

I would probably try a site like this one...

http://carcomputerexchange.com/jeep...ee-ecm-pcm-engine-control-module/prod_89.html

 

[98NWCherokee]

Sidewinder, I didn't backprobe A17. I thought about popping the connector cover off but I didn't want to cause more damage. I pulled the connector and checked for power at A17. I only had trace voltage I also checked the grounds and they were good at A31 and A32 and battery voltage is going to the PCM at A22 I believe.

I found this place....

http://autocomputersystems.com/1998-jeep-cherokee.html

I like their warranty better. Any opinions please speak up. I'm on the fence on this as I continue to test.

Does anyone know where the RKE module is in overhead console equipped XJ's? I'm still wanting to pull that and see what happens.

 

[Sidewinder CC]

Sidewinder, I didn't backprobe A17. I thought about popping the connector cover off but I didn't want to cause more damage. I pulled the connector and checked for power at A17. I only had trace voltage I also checked the grounds and they were good at A31 and A32 and battery voltage is going to the PCM at A22 I believe.

I found this place....

http://autocomputersystems.com/1998-jeep-cherokee.html

I like their warranty better. Any opinions please speak up. I'm on the fence on this as I continue to test.

Does anyone know where the RKE module is in overhead console equipped XJ's? I'm still wanting to pull that and see what happens.

If you removed C1 from the PCM you also removed the two 12 volt power sources to the PCM (A2 and A22). A2 is from fuse F11 in the JB (Start-Run A21 circuit) and A22 is from fuse 22 in the PDC (Batt A0 circuit).

A 5 volt supply also comes from PCM C2, B31. It provides 5 volts to the Vehicle Speed Sensor, which may be back feeding to the entire sensor return circuit (which are all spliced together at S111, S114, and S138), which may end up at C1 as a residual voltage.

Before changing the PCM, I would connect C1 and verify I have 12 Volts (Minimum 10) at PCM A2 and A22 by back probrobing the connector at these pins. And verifying that, in fact, I don't have 5 volt at A17. If the 12 volt sources are intact and providing voltage to the PCM and you still don't have 5 volt output at A17, then I would consider a replacement PCM.

~~~~~~~

If you drop the cover off of the overhead console you will see the RKE module near the center of the overhead console.

 

[98NWCherokee]

Sidewinder, again thank you for all the help. This is heavy diagnostic work for me so I appreciate any help I can get. To answer your question earlier, I did check the health of the CCD bus today. At pin 3 and 4 or 5 I get 2.44 volts and at 11 and either 4 or 5 I get the same.

I got my hands on an actual DRB III today and attempted to communicate. With the PCM connected at all 3 connectors the DRB freezes when trying to identify the engine controller (makes sense if shorted PCM). When I disconnect the PCM and try to gain access to the TCM (to test the network and/or module short(s) the DRB comes back with no response. I interpret this as the DRB pinging the TCM and getting no response (possible with shorted PCM) and coming back with no reply. This tells me the network is intact. Is this a viable conclusion given my volt reading at the DLC?

I also went through the COMPLETE "Cranks but won't start with no DRB connectivity" trouble tree in the factory service manual. It condemns the PCM. For good measure I pulled all 6 injectors, the O2 connector along with all the sensors on the 5 volt feed. I pulled every single relay in the PDC. I put an Ammeter in series and with key off I'm pulling 1.56 amps. When I pull connector 1 at the PCM it drops to .004 amps.

I do have roughly 11.5 volts at the PCM A2 and A22 and I have trace voltage at A17. The 12 volt source is intact, as is PCM ground. How can I check for shorts along the 5 volt line? How do you Ohm check a Hall Effect sensor like the crank sensor? I know voltage is not present, but I want to be more confident I don't have a short before I plug in a newly flashed PCM.

I ordered a replacement PCM and it will be here Tuesday fully flashed and rebuilt with a lifetime warranty for $260.

Have I done all that I can do to ensure it won't blow when I connect it?

 

[98NWCherokee]

PCM arrived this evening as promised with a warranty sticker on it.

I'll update this thread tomorrow when I plug it in.

Fingers crossed.....

 

[cushdaddy]

I hope yours goes as well as mine.

 

[98NWCherokee]

Installed the PCM today and it starts again.

I was happy, until I realized I now have no interior dash lights. All running lights and headlights work, and the headlight switch still has both detents and turns on the interior cabin lights....but no dimmer and no dash lights. When I pull the switch the radio display dims to almost nothing, but the odometer and overhead console do not dim at all and I have no cluster or HVAC lights. The 5A fuse in the junction block is not blown.

Headlight switch?
I wasn't anywhere near the headlight circuit during PCM diagnosis........how could it fail all the sudden?

Also found a huge screw in the tire and now I'm at work until 11pm when I get to drive home with no dash lights and a flat spare tire.

I can't win it would seem.

 

[GrimmJeeper]

common failure of the headlight switch kills the interior lights. it's not really a question of if, its more of when.

 

[98NWCherokee]

That's good to hear GrimmJeeper. It just puzzles me that I would have a dead battery, then crazy door locks, then a bad PCM, then no interior lights.....all in the space of one week while the Jeep was at the shop waiting for parts.

I've read a few threads about questionable replacement switches. I've had good luck with NAPA in the past and they carry a replacement switch for $15. Would that be a bad direction to try? I'll make sure the fuse isn't blown tomorrow and check for power first of course.

I managed to get a co-worker to run me over the Les Schwab so at least I won't have a flat tire when I leave work at 11pm tonight.

 

[cushdaddy]

Glad to hear it worked. I am starting to think that the Schumacher charger switching had something to do with it.

 

[98NWCherokee]

I've been thinking about it quite a bit. It's way too eerie that we both used the same brand and vintage charger/jump box and both ended up with internally shorted PCMs

however, something had to bring my battery down to 5 CCA after being in normal daily use. I'm quite confident the 1.5 Amp draw at the PCM is what took out the battery which means it was fried before I even touched it with the jump box.

That being said, I probably won't use it again just to be safe.

Picked up a headlight switch at NAPA today and will install it tomorrow after a little circuit testing. I had to leave early today to get home before dark. Driving with a black dash is not fun. On the plus side, I've logged about 75 miles and probably two dozen starts with no additional problems so good progress.

 

[98NWCherokee]

Headlight switch was not necessary. The 5 Amp fuse for the interior dash lights was blown. I must have disrupted it while testing every single fuse during the PCM diagnosis. Popped a new one in and we're back to daily driver.