Occasional misfire cause by PCM? - Jeep Commander Forums: Jeep Commander Forum
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post #1 of 10 (permalink) Old 07-09-2016, 07:27 PM Thread Starter
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Occasional misfire cause by PCM?

Hi everyone,

I have been dealing with an intermittent misfire over the past month or so. It only happens on hot days in Vegas (so over 100 degrees F) and after driving for a bit either in stop and go traffic going up a long hill.

Before the misfire started I had the following done at the dealer:
PS flush, Trans fluid and filter replacement (no flush), transfer case fluid replaced.

I noticed a slight misfire within a week of that service. It took a week and lots of driving before it finally threw a CEL. Went to autozone and the following codes were active:
P0202, P0203, P0206, P0207, P0208 which are the codes for the fuel injector circuits, stating the was a short or disconnected plug.

I had them clear the codes and continued to drive it around. It started getting worse and worse over the course of another week and I brought it to my mechanic who found a vacuum leak. Fixed the vacuum leak but still had an intermittent misfire. (obviously less frequently)

A week later it through P0300 (random misfire) so I brought it back to the mechanic. He ran through a bunch of testing and didn't find anything and couldn't reproduce the misfire. So he cleared the codes, and I went on my way. I also replaced the TPS since it was easy and could have been the issue.

It threw P0300 again a few days later and I brought it to the dealer. The dealer hooked up the scan tool and I remember seeing stored codes for the ICM and FCM but didn't get a printout of the codes. The dealer looked only into the P0300 code and said they couldn't find anything wrong and told me the spark plugs are a little worn. So I changed the spark plugs and replaced all the ignition coils with champion plugs and mopar coils. That didn't make a difference.

Drove it around for a few more days and brought it back to the dealer after the CEL went on and back off on its own. The stored codes were:
From PCM: P0206, From WCM: B1A25, From FDCM: U0431, U0141

I had the dealer look into the problem again and again they didn't find anything. They said they specifically checked the fuel injector circuits and O2 sensor circuits (after I specifically told them too) Still didn't find anything wrong. Had them clear all the codes and went home. This was yesterday. Of course CEL comes back on on way home, its missing constantly. Went to autozone and got the active codes:
P0300, P0202, P0206, P0205

After autozone i started heading home. missing got really bad and suddenly the missing stopped. CEL on the entire time. I assume it must have went into a "limp" mode.
This morning I brought it to the dealer near my house to get all the stored codes from last night:
From PCM: P0300, P0202, P0205, P0206, Frm WCM: B1A25, From FDCM: U0431, U0141

I also stopped by the private mechanic I know this morning and he said it sounds like the PCM is going bad.

While driving it around the misfire seems to only be related to the outside temp and the engine temp. I have tried driving in different gears when the misfire starts, tried it in reverse, park, tried different rpm ranges. I tried jiggling the harnesses at the PCM and the fuel injectors when it wasn't missing. From what I can tell the only causing factors are engine temp a tick mark on the gauge above where it used to be at normal operating temp when it was in the 80's outside, and it being over 100 degrees F outside. Doesn't do it when its under 100 or when the engine temp is under a certain temperature. It has never stalled.

Its a 2007 Commander 4.7 4x4.

Descriptions of the DTCs:
Active codes:
P0300: Random misfire
P020X: Injector circuit has detected a short circuit, open circuit, or overload. for injector on cylinder X
Stored codes:
U0431: From FDCM: The FDCM is receiving no message or implausible data for Ambient Temperature from the FCM
U0141: From FDCM: Buss messages not received for 2-5 seconds
B1A25: The SKREEM does not receive a transponder response after 8 consecutive transponder read attempts

Now the questions:
1) Limp mode for the engine on the commander, if this happened yesterday how could I tell?
2) The dealer mentioned there were four software flashes available for my vehicle:
Software flash for PDM, Software flash for FCMCGW, Software flash for CCN, Software flash for PCM.
They had no idea if they would help. Does anyone think any of these would help, they are $30 each to try?
3) Is there a way to verify if the PCM is the issue?
4) If the FDCM is complaining about not receiving information from the FCM and the FCM was the source wouldn't another module such as the TCM or PCM complain about that as well?
5) Could issues from the FDCM indirectly cause a random misfire? Where is the FDCM so I can check the connection?
6) This all started after dealer service to trans and x-fer case. The transmission sucking in air from a crack in the filter or an old seal can cause the engine to stall. Could the occasional bubble cause a miss without throwing any DTCs?
7) anything else I should look into?

Thanks!
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post #2 of 10 (permalink) Old 07-13-2016, 02:21 PM
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A while back I had a Grand Cherokee with a 4.7 liter that did pretty much the same thing. It kept giving me a random misfire code and the injector open / short circuit codes. I would clear the light and after about 15 minutes it would come back on but there was no rhyme or reason to it. Sometimes the injector codes would be on some cylinders and then I cleared it and it would be on different ones when it came back on, it didn't make sense. After clearing the engine light it would run great for about 15 minutes until I came back on and then it would start to misfire. Eventually it got bad enough that it would almost stall in traffic. It ended up being a bad MAP sensor even though it never gave me a code for that. Someone in one of the Grand Cherokee forums suggested the map sensor and that's what fixed it. I got it out of the junkyard out of a 4.7 Dodge Ram. You might want to try that before replacing the expensive PCM. I don't know anything about the front control modules or any of the control modules you're talking about because the Grand Cherokees don't have them. What I do know (and it could be different because yours is newer) is that limp mode only occurs for transmission problems as far as I know. I've never heard of limp mode for engine issues. If you want I can give you the link to the factory service manual for the WK Grand Cherokee which is what I use for my mother's 2006 Commander. It's pretty much all the same wiring.
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post #3 of 10 (permalink) Old 07-13-2016, 04:35 PM
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Have you tried a fresh set of spark plugs yet? How old are the plugs in the engine now?


Injector codes mean there is something with the injectors or the circuit to the injectors. You could have loose connectors, shorted wires, dirt or oil in the connectors. You could have dirty injectors. You could have low fuel pressure and causes the pulse width of the injectors to go too high. Did this dealership even put a fuel pressure gauge on the engine to confirm the fuel pressure?


The PCM detects misfires by the differences in crank speed, so anything that causes the crank to slow for a moment, which is what happens when a cylinder misfires will register as a misfire on the PCM. A bad accessory could cause it, just as well as ignition and fuel injectors are vacuum leaks.


The earlier Commanders with Hemi's did have a bad run of PCM's where the circuit boards on the PCM would crack and cause stalling without setting codes. That doesn't sound like your problem. And its a common jump to conclusion when people can't figure out the problem they just jump to conclusions the PCM must be bad.


The Dealer is suppose to do software updates for free if the vehicle is already in for service. They should only charge you if you come in just for a software update and nothing else, and then only charge you one fee for inducting the vehicle into service to load the free software updates, NOT a fee for each individual software update. I wonder what Chrysler Customer Service would think if they learned this dealer is hocking software updates, one at a time??


The Dealer deserves some payment to induct your vehicle into service. So if you just show up and ask them to induct the vehicle into service to give you free software updates, then yea, they deserve some money for the labor to induct the vehicle into service.


If you're already paying for them to induct it into service for some other reason/problem, which it sounds like you already had them do it, they're suppose to update the free software while its already in for service.


They are taking free software updates and selling them like they are a product in the catalogue, they're NOT, and it doesn't sound kosher to me.....
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post #4 of 10 (permalink) Old 07-15-2016, 02:35 PM Thread Starter
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Thank you for the input.

The MAP crossed my mind to clean. Havent done it yet though.

One of the stored codes says a bad signal for ambient temperature, and I don't know if that could be related to the IAT (intake air temp) sensor? Is there a way to clean the IAT sensor? Does that sensor tell the jeep what the outside temp is when you hit the C/T button under the radio and the trip meter reports the outside temp and your heading (N,S,E,W)? Because that has been 8-10 degrees high ever since it got to desert temps.

When this first started happening i had a mechanic perform a fuel system service where they run a cleaner through the fuel system. Then after that I put in a lot of injector cleaner.

After the first code I changed the spark plugs and the ignition coils.

I also replaced the TPS because the resistance on the old one didn't seem as stable as I would have expected. But it didn't fix the misfire.

I had a mechanic and a dealer look at it. The mechanic did a vacuum test and then drove it for a bit to try to feel the misfire but couldn't get it to misfire. The dealer said they checked the fuel injectors and injector circuits, as well as the O2 sensors (I asked them to). They also said they couldnt experience the misfire.

I went through and jiggled and futzed with the connectors at the PCM, the injectors, the ignition coils, and most other large connectors I could reach both in the engine bay and from under the vehicle.

I haven't checked the fuel pressure yet. I have a fuel pressure gauge so I will do that. How does the fuel pressure affect the duty cycle of the injectors?

It seems to throw the fuel injector circuit codes before the random misfire code, and I have never had the P0300 code by itself or appear from the key trick. the scanner at autozone will see it though.

Mongo, is it written anywhere that the dealer isn't supposed to charge extra for the software updates if your vehicle is already in for servicing? They wanted to charge me $30 an update (4 updates) after charging me the $130 for the diagnostic which didn't show anything. I ended up bringing it to the other dealer to have them take a shot at it because I was hoping to have it fixed by this weekend. If they should be able to throw the updates on as part of the diagnostic service then I would like them to do that.

Thanks again!

Last edited by mgomez; 07-15-2016 at 11:21 PM.
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post #5 of 10 (permalink) Old 07-16-2016, 01:09 AM
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I'm going through the same issues with my '07. I am lucky in that I had bought the extended service contract which is still in effect.
My thoughts was PCM but, second lucky part, I have a friend that is a tech at the local Jeep dealer.
That being said, I'm still dealing with issues.
He looked at it this morning and decided to try the fuel pump first(covered by the contract). He said it showed a reduction in fuel pressure and with the random nature of the codes(same ones you had) he thinks its more likely than the PCM
I should get it done next week so I'll update y'all after.
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post #6 of 10 (permalink) Old 07-16-2016, 01:30 AM
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The O2 sensor provides feedback to the PCM as to the Air/Fuel Ratio. If it sees that the A/F ratio is too lean or rich, it corrects the amount of fuel being injected to get the right A/F ratio. The PCM does that by changing the injectors pulse width (how long it opens the injector valve). So if the fuel pressure changes, that will change the amount of fuel that is injected for the pulse width that the PCM sets. But again, with the O2 sensor, the PCM will adjust the pulse to get the right amount of fuel that is needed injected.

So, if you got low fuel pressure, the PCM will adjust to it and increase the pulse width to get the right amount of fuel into the motor. But you can run into a problem, what if you need the max amount of fuel the injector can supply. Because of the low fuel pressure, the injector is already opening longer than it was designed, you go to the max amount of time the injector can open, and because the fuel pressure is low, not enough fuel gets injected. The A/F ratio will go lean and that could cause detonation or misfires.
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post #7 of 10 (permalink) Old 07-16-2016, 08:31 PM Thread Starter
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The dealer has had it since Tuesday last week so I have been unable to do any more testing on it. But yesterday (after the 3rd or 4th test drive this week) they were able to replicate the issue but haven't been able to pinpoint the cause yet. They told me they were going to plug in a reader that logged run time data and hopefully would give a clearer picture of what is going on. They should be doing that Monday.
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post #8 of 10 (permalink) Old 08-17-2016, 07:36 PM Thread Starter
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In case anyone wants to know the solution: there was a bad ground inside the pcm causing the injectors to stay closed occasionally. Replace the pcm a few weeks ago and haven't had an issue since.
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post #9 of 10 (permalink) Old 08-20-2016, 05:46 PM
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Im having the same issue will misfire sometimes code p0300 p0207 p0208 p206 and p202 is there anyway to test the pcm ?
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post #10 of 10 (permalink) Old 08-21-2016, 12:01 AM
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Originally Posted by Serher View Post
Im having the same issue will misfire sometimes code p0300 p0207 p0208 p206 and p202 is there anyway to test the pcm ?
I'm sure the Chrysler/Jeep dealership can do it.

It will probably cost you $120.00 for the diagnostics test.


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