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Old 01-14-2017, 01:52 PM
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I may have lost my PCM - I need help diagnosing no start issue

2005 Rubicon Sahara LJ, Manual Tranny.

Engine mods: MCAI

PCM was replaced by the dealer a couple of years ago under federal emissions warranty. All regular maintenance has been accomplished by me. The Jeep has never had a problem.

Temperatures for the past few weeks have regularly been in the single digits and even into the negatives.

The issue:

Thursday night I drove my jeep home, threw a gallon of gas in it due to a slow gas pump, and parked my Jeep in the driveway with just a few gals in the tank. At 9 pm I plugged in my block heater.

Friday morning I went out to the Jeep and it wouldn't start.

The Jeep cranks just fine, it just won't fire. A few days ago it felt like it wasn't going to start, took a while to catch, but fired off with no subsequent problems. This time, it's not even trying to fire.

Here's what I know:
Fuel pump is making noise
Fuel pump relay is good
No blown fuses
Does not start using starting fluid. Doesn't even try to start.
Tail pipe is dry
Fuel gauge reads full when the tank is less than 1/4. Sometimes slowly drops to 1/2 tank. Isn't accurate.
No loose connections that I can see
Codes (summarized):
2096 - Lean condition
0627 - Fuel pump circuit open
0112 - IAC low
0516 - Batt temp circuit low
0072 - Ambient temp low
0462 - Fuel level circuit low
0562 - Voltage low
0340 - Camshaft psn sensor
0335 - Cranshaft psn sensor
0838 - 4wd
0117 - cooland low
0107 - mani low
0122 - tps voltage low
0580 - cruise ctrl

Yesterday I sent the Jeep to a mechanic. (I know, bummer)

The mechanic says he can't get any voltage off the TPS and some other sensors. Something about not getting 12v from the computer (phone was fuzzy). His snap-on computer can't clear the codes and disconnecting the battery also hasn't cleared codes. He hasn't had a chance to check for spark before the shop closed. He feels confident that it's the PCM.

I'm having a hard time believing that overnight the PCM went bad. However, the mechanic's inability to clear codes has me concerned.

The mechanic doesn't open again until Monday. I need some ideas to have a good conversation with him about potential options. Without having the Jeep in front of me, I'm out of schlitz.

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Old 01-14-2017, 03:44 PM   #2
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Assuming you have 12v (battery & key on/start) at the PCM & good grounding & the PCM connectors are clean & dry, you need to see if you are getting 5v sensor output from the PCM (2 locations). Then check the sensor grounds at the PCM. The 5v supply & sensor grounds are mostly all tied together through various splices so if the either the supply or ground is bad it can affect some or all sensor readings. Since most, if not all sensors are showing codes with low voltage I would guess one of those is the issue.

It may well be that you can reset the codes but as soon as you turn the key on they all return as the PCM sees that apparent low voltage from them.

Usually, at least on some of the earlier yrs, if you lose the 5v supply the gauges & data link won’t respond which is not what is happening but still might be your problem.

Some have used a USB charger which happens to also be 5v to supply the missing power to the sensors & everything works & it starts right up. Here is an example in case that is what is happening & you or your mechanic wants to try that to verify this.

https://www.wranglerforum.com/f210/no...5l-705906.html (at post 68)

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Old 01-15-2017, 07:00 PM
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Thanks for the reply. Very helpful!
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Old 01-16-2017, 11:49 AM
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So right now it looks like good 12v, good ground, and good ref voltage.

Still can't clear codes, but he can read them.
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Old 01-16-2017, 01:00 PM   #5
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5v outputs from PCM???
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Old 01-16-2017, 01:08 PM   #6
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The P0562 is also concerning. I wonder if the PCM is getting the full 12v input. Maybe a bad connection at the connector.

P0562 -- Charging System Voltage Too Low -- Supply voltage sensed at ECM too low.
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Old 01-16-2017, 06:57 PM
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5v, correct. Connections are all clean and solid.

The PCM isn't talking to the sensors. For example, nothing from the TPS even though it has ref voltage.

The trouble codes cannot be reset. That's what is strange.

Also the fuel gauge reads full when the tank is nearly empty.
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Old 01-16-2017, 07:19 PM   #8
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Got it. It is looking like the PCM.

Be sure to report final results when you get it figured out & fixed.
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Old 01-19-2017, 02:08 PM   #9
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Any updates? I've got similar issues just waiting on a replacement PCM.. think i tracked one down.
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Old 01-19-2017, 03:42 PM   #10
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The issue:

Thursday night I drove my jeep home, threw a gallon of gas in it due to a slow gas pump, and parked my Jeep in the driveway with just a few gals in the tank. At 9 pm I plugged in my block heater.

Friday morning I went out to the Jeep and it wouldn't start.

-----------------------------
I've alwasy been taught you should never leave just a few gallons in a tank if its gonna freeze. Cold air increases water condensation. Your fuel could be water logged. Try draining the fuel tank and filling up with fresh petrol.
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Old 01-19-2017, 10:51 PM
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Dealer confirmed the PCM is shot.
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Old 01-24-2017, 07:43 AM   #12
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I'm having same issues. Thanks for this thread. I'm going to take a look at the PCM. Already changed the crank sensor. 2 times. Then it worked for a few weeks. Now it's not. Had this problem in 2000. Maybe it's done again.
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Old 01-28-2017, 03:43 PM
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The Jeep still isn't finished.

Thursday morning: PCM arrives, tech has a family emergency. Nbd, I understand that things happen. I'm told that the Jeep will be done the next morning

Friday morning: the dealership's computer won't program the PCM. Something about the dealership's computer requiring new software or a software update.

Friday evening: "we need your Jeep for the weekend. We need to contact Chrysler on Monday morning to solve the problem"

If not resolved by Monday evening I'll be asking for my Jeep to be transferred to another dealership that has the ability to complete the PCM repair.
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Old 01-28-2017, 06:39 PM   #14
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My Alternator went, then battery, had three alternators finally took it to a shop and told me, my PCM is shot. One dealer will not do it the other quoted about 1500 if we could get one as there were only two in the country. No charge getting to the alternator. I have 2001 jeep sport 4.0 not sure what I am going to do.
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Old 01-28-2017, 06:50 PM   #15
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...not sure what I am going to do.
Maybe do an internet search for "ECM repair."
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Old 01-29-2017, 07:49 AM   #16
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External voltage regulator conversion?


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Old 01-29-2017, 08:22 AM   #17
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Sounds like 05 and 06 has serious pcm problems!!!!
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Old 02-02-2017, 11:40 PM
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The PCM problem is resolved. The fuel gauge quit working due to a frayed wire that shorted out above the tank. The tech "is confident" that this didn't kill the PCM but from what I've read online, it's very possible that this was the trigger. Otherwise it's way too coincidental for the two components to die at once.

During all of this the dealership was nice enough to look into a driveline vibration that i have. Turns out a transmission bolt fell out and two others loosened. This ended up cracking my bell housing.

The hope is to pick the jeep up tomorrow and get the transmission out tomorrow night. Hopefully I can have the bellhousing welded next week.
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Old 02-23-2017, 10:44 PM
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Quick update. I was able to have the trans welded and everything is smooth as silk now.
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Old 02-24-2017, 07:17 AM   #20
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Glad to hear
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Old 02-24-2017, 02:51 PM   #21
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Loose Transmission Bolts

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Originally Posted by stangmata View Post
The PCM problem is resolved. ...
During all of this the dealership was nice enough to look into a driveline vibration that i have. Turns out a transmission bolt fell out and two others loosened. This ended up cracking my bell housing...
Interesting find on the trans bolts. Good thing it was caught in time before the powetrain ended up in two pieces.

So I was replacing my Starter last week and accidentally loosened a bellhousing bolt. Incidentally, it didn't take much. I was surprised. I wonder if I should check the rest of my bolts and everyone else with 05's as well.
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Old 02-24-2017, 06:01 PM   #22
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Did they warranty the PCM since its only 2 yrs old?
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Old 03-02-2017, 10:29 PM   #23
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Sounds like 05 and 06 has serious pcm problems!!!!
For sure they do have alot of issues cause im one of them having an issue with my pcm. In my case it was having issues with a misfire on 1,6 cylinders and i had swap ignition coil and nothing untill i was able to solve the issue by taking the pcm apart and looking at the circuit board and it was burn where the circuit to the ignition coils. Now i need to buy a new pcm but im not sure where to go with one in ebay or have a new one from the dealership. Used one in ebay is like $749.99 and dealership is asking $862 for a new one plus reprogramin fee. I hear bad experience on buying a used one from the internet too so im still thinking about it and mean while my rig is park in the garage 😩
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Old 06-29-2017, 02:34 PM   #24
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For sure they do have alot of issues cause im one of them having an issue with my pcm. In my case it was having issues with a misfire on 1,6 cylinders and i had swap ignition coil and nothing untill i was able to solve the issue by taking the pcm apart and looking at the circuit board and it was burn where the circuit to the ignition coils. Now i need to buy a new pcm but im not sure where to go with one in ebay or have a new one from the dealership. Used one in ebay is like $749.99 and dealership is asking $862 for a new one plus reprogramin fee. I hear bad experience on buying a used one from the internet too so im still thinking about it and mean while my rig is park in the garage 😩
What did you end up doing? My dealership is quoting me $1300 and that is just for the replacement. Similiar cost to another thread here.

I did send my PCM in for repair to Your Part Source via Ebay.

Codes were P1684, P0891, P0562, P0218, P0700, P0883.
2006 Wrangler X, about 172K mi
4.0L, I6

Tech: Replaced IC Transmission control Chip

No CEL for about 6 days after I received it back.

Codes thrown: P0700, P0883, P0562

They were super helpful but I think this is a blown PCM. Has anyone gotten a replacement PCM via NAPA?

The disconnecting of the battery cables used to work but it doesn't seem like it anymore.
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Old 06-30-2017, 06:41 AM   #25
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What did you end up doing? My dealership is quoting me $1300 and that is just for the replacement. Similiar cost to another thread here.

I did send my PCM in for repair to Your Part Source via Ebay.

Codes were P1684, P0891, P0562, P0218, P0700, P0883.
2006 Wrangler X, about 172K mi
4.0L, I6

Tech: Replaced IC Transmission control Chip

No CEL for about 6 days after I received it back.

Codes thrown: P0700, P0883, P0562




They were super helpful but I think this is a blown PCM. Has anyone gotten a replacement PCM via NAPA?

The disconnecting of the battery cables used to work but it doesn't seem like it anymore.

I think you are better going to the dealership. Read the last page of this thread...

https://www.wranglerforum.com/f282/do...1801033-5.html

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