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Old 11-19-2019, 12:30 AM
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PCM trouble?

I have a 2006 Wrangler. Yesterday when I started it up, it immediately had a misfire. I was able to drive about 15 ft before it died. It started back up but the misfire seemed gone, but it died again. It wouldn't start for a minute and I made it about half a mile before it died. Repeat this for a while just so I could get home.

I noticed that the cluster was half dead. The gauges all dropped, but the lights were all there. (check engine, and gas light) I have a code reader at home, so I hooked it up. I turned it on and after a minute or so, the cluster dies as usual and the com dies as well. Shortly after, the RPM drops, tries to spike to catch up and then dies.

That same pattern seems to happen every time I start it up. Everything seems fine for a few minutes, the cluster dies (and immediately the data link dies) then shortly after, the engine stops.

No sensors were firing prior to all this, and the first time it died and I was able to hook it up, it had 13 different error codes.

I'm not convinced it's and sort of sensor because it starts up and runs a while before everything eventually dies. I did notice the RPM's slowly lower before it seems to choke and die. Also, the battery and alternator are functioning fine during all of this.

Does this sound like the PCM is going out? What other things can I try to narrow this down? I can't seem to find a PCM under $400 and of course, I'd still have to get it programmed somehow.

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Old 11-19-2019, 06:45 AM   #2
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Have skim?


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Old 11-19-2019, 10:27 AM   #3
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What were the codes? I'd like to see if there is any relation between them. For example, if you have a shorted 5v reference line, it will mess up a lot of sensors.

You don't want to replace a PCM without at least troubleshooting some of those codes.
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Old 11-19-2019, 11:10 AM   #4
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PCMs are rarely at fault. List the codes, I would assume your scanner stores them. CPS sensor, chaffed wiring harness, unplugged wiring harness, bad ground. Do your due diligence first.
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Old 11-19-2019, 12:02 PM   #5
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Old 11-19-2019, 08:22 PM   #6
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I would start checking all the grounds making sure there's no rust behind the ground wires and that they are all tight and also check all connectors to the pcm and any other wire connectors you can find.
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Old 11-20-2019, 03:00 PM   #7
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Welcome to the forum TekTech,

Is your Wrangler 4 cyl or 6 cyl? Automatic or standard?

Good Luck, L.M.
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Old 11-21-2019, 01:07 AM
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6 cyl, standard, no SKIM.

The codes weren't stored on the scanner tool. It only keeps the last reading, and unfortunately the note I had on my phone got deleted. The only thing I can get is U0155 Lost Communication With Cluster/CCN. That happens then the gauges die.

I've been checking grounds and so far, they seem fine. However, I haven't check all of them.

I did just check the CPS and it looks like it needs to be replaced. I'll follow up tomorrow and let you all know if that is really all that was problematic.

---
I appreciate all the feedback. I didn't think I would actually get many or any replies. But it it my first time here, so I'm grateful!
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Old 11-21-2019, 04:22 PM   #9
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Sounds like pci bus issue

Pci has a connection in radio 22 pin I think it is pin 14

Pci also connects to cluster and pcm and air bag module plus the connector for a skim module


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Old 12-03-2019, 06:31 PM
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UPDATE:

I had to get a new multi-meter since I lost mine, and the only other one I have is over 30 years old... It's not calibrated anymore.

I checked a few grounds and they look fine. I did notice something. So I changed the alternator, because the code reader I have will show the diagnostics for it. It was reading about 13.20 - 13.27 V. The odd part is my multi-meter is showing 13.5x V. So the computer is reading the voltage lower than the actual output. Additionally, 13.5 is lower than what it's supposed to be, Correct?
I had just replaced the alternator a week ago because the computer was reading it low. So I may just need to take it back and have it tested. OR is it possible that something else could cause an alternator not to generate the power it needs to?

I was able to get a new code to come up. P0508 - https://www.wranglerforum.com/f210/p...p-1619849.html
Currently testing the IAC to see if that's a problem.
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Old 12-04-2019, 06:15 PM   #11
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I actually has a similar thing happen on my 05 2.4L. Had an odd looking half dead cluster and jeep died and wouldn't start. Ended up being a bad connection on the battery terminals (Although they looked fine). A slight bit of corrosion and the terminals not being tight enough caused it. I ended cleaning them up and tightening them back down on the side of the road and everything ran perfect. I have since changed all the heavy wiring and new terminals but i would check it. Don't know if/how that's related to the alternator voltage miss-match but i'm sure wacky things happen when its not getting proper power.
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Old 12-09-2019, 11:52 PM
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Another Update:

I brushed off the terminals, even though they were spotless. No difference.

I checked the voltage going to the PCM and it was 4.985V +- 0.002V. That was steady the entire time, so it didn't appear that the power to the PC was bad. I didn't get a good reading of the ground while the engine was running, but while it was powered off, it seemed like everything was fine.

At this point, the jeep wont run long enough to keep the battery charged so I'm having to jump it off just to troubleshoot problems. (could a battery be causing a problem like this even through I could still start it numerous times until recently?)

I did manage to get the computer to throw 5 codes:
u0155 - the useless code from before

All 4 of these are the heater control circuit:
p0032
p0038
p0052
p0058

I could get it to keep running after the pci bus died, but it was running really rough. So I turned it off.

Still looking for things I can test.
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Old 12-10-2019, 08:33 AM   #13
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First voltage to pcm is bat/alt voltage 12-14 volts the 5 volts to sensors is pcm output no input


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Old 12-10-2019, 08:42 AM   #14
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Those codes are common with pcm failure in the pci NGC PCM used in the 04-05 PT cruiser 2.4 especially with the 2.4

The NGC PCM has a heat failure issue that results in o2 sensor heater high and low codes

Only effective solution is replace pcm

Wife has a turbo cruiser she had since new
2 years ago started throwing codes for o2 sensor heater voltage both (either high or low) if forget which and would go into limp mode and a battery disconnect would resolve issues short term but became more and more frequent with hot starts also all the battery disconnects made it real hard to find a day it could pass emissions

Got a new pcm from FS1 and codes became constant but reversed high bs low voltage o2 heater
But no more limp mode

Then the replaced it again with one that has had no issues for last 18 months

It is a known heat failure with the crappy NGC PCM
TJ started using this pcm in 2005




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Old 12-10-2019, 09:13 AM   #15
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A couple of points and some things I'd try:

First, the 5v is created by the PCM. It is sent to sensors. It's helpful to understand if it's working because if it isn't nothing is going to run. It's one thing to check on the health of a PCM. The PCM still requires 12v on several wires and proper grounds to work properly.

One thing I'd try is unplugging the cluster. Making a stab here that the cluster is failing and when it does it's bogs down the PCI BUS which is causing problems with the PCM. Unplug the cluster, start up the jeep. Does it start? Does it run better? Ideally the way you'd really know this is to use an oscilloscope on the PCI lines to see what is going on. But guessing you don't have one so unplug the cluster.

I'd also troubleshoot those heater circuits on the O2 sensors. Why do all of them show high voltage? Those codes get set when the o2 heaters are off, yet the PCM sense voltage. This might be an internal PCM issue but I'd be checking voltage on those lines at the sensor (with it unplugged) and back at the pcm. If I am seeing no voltage they I would think it's internal issue to the PCM.
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Old 12-10-2019, 09:16 AM   #16
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One easy test is just disconnect battery and reconnect and see if the fixes issue short term

The heater circuit on o2 sensors is not involved with the pci bus


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Old 12-10-2019, 09:28 AM   #17
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Read thru these many pages and weep

https://www.allpar.com/forums/thread...031-37.152314/


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