PCM Issues

[milradioman]

I was driving in hot weather up hill last week (dont know if temp related), when the "Check Engine" light came on, I noticed the volt meter was all the way down to the left most line (same as engine off position). When I arrived at the top and started on the decent; I noticed the overdrive does not work (auto trans), also the cruise control is not working, and the trans appears to slip on take off.

 

Referencing the PCM (power control module) info; the pcm controls the above items, I have not noticed any other items on the list malfunctioning.

 

Before I spend $400 or more for a new pcm, I would like to make sure it is the module or bad connection, ground...

What is be best method to confirm the pcm is good or bad?

 

Or is there something else that could cause the above problems?

 

Brian

[Mopar1973Man]

Check your fuses.

 

Check your error codes there might be a clue there.

 

Check your negative terminals. All grounds for the ECM, PCM and VP44 are in the battery cable there is no external body grounds.

[milradioman]

What fuses am I looking for? Engine fuse block only?

 

Error codes all relate to charging issue, no suprise there, the only one I cannot read is DTC on ECM or PCM...

 

The grounds "look" clean I have not had time to remove and clean them.

 

I question why some stuff works and some does not, is this normal when a pcm fails?

[mopartechnician]

Pull your pcm connectors and make sure pins are good and connections are tight. It could be one thing causing all the other stuff to happen

[milradioman]

I just pulled the air filter housing to get to the pcm, found the air filter really needs to be replace(!)

Removed the pcm, cleaned the ground contacts, the screw with the ground lug had some corosion looking film on the aluminum surface, also cleaned the other two screws applied dielectric grease to all cleaned surfaces.

 

Treated the ground wire near the battery the same as above.

 

Removed all three plugs on the pcm, inspected the contacts, all are clean, and straight, made sure the connectors are put back in tight.

 

Put the pcm back in and will try it tomorow.

[milradioman]

Well, I started it up, and.....No change, still not charging etc.

 

I still need to have that DTC code read, but not looking good.

 

Anything else I can try to determine if I need to buy another pcm?

Where is the best place to buy a pcm that is going to be reliable, this is my work truck.

[kerley]

I am thinking that you may have a defective battery.

[mopartechnician]

Agree next step is codes and have the battery/charging system inspected

[milradioman]

Both batteries were replaced last year, I have been charging them with a battery charger each night as I am driving it each day.

 

I checked the field wires at the alternator and both have less than 2 volts reference to ground. The charging system and voltage gauge is the easiest indicator I have to note if there is a problem.

The list of issues is more than just the charging system which leads me to think the pcm is not working right. Today is the first time I have driven the truck for any distance and noticed the A/C shut off, it was blowing nice and cold. The A/C is also controlled by the pcm.

 

I read the codes with the key method and show: P1682=charging system voltage too low. P0753=Transmission shift 3-4 relay circuits. P1765=Transmission 12 volt supply relay. P1693 DTC detected in ECM or PCM.

 

I am hoping to perform a "test" of some sort to determine for sure if the problem is really in the pcm before I replace it.

 

Also; I have a 1999 ram almost the same vehicle options, Anyone know if that pcm will work in my 01?

[Mopar1973Man]

Field lead have to be tested unhooked. Because the alternator field is nothing more than a short. So now the blue wire should be 12V (POSITIVE) and the green wire should be a variable GROUND.

 

[milradioman]

Ok, I can try to power the alternator manually and I am sure it will work fine, because I don't think the problem has to do with the alternator; as all the other stuff happened at the same time and is on the pcm control list too.

 

If I can determine the pcm is the source of the problem; where is the best place to buy one?

[Mopar1973Man]

In a pinch you could do a old school regulator but be warned it will not charge the same as the temperature controlled PCM.

 

http://articles.mopar1973man.com/general-cummins/34-engine-system/134-voltage-regulator-mod

[Yankneck696]

Looking at the schematic above, I would try swapping out the trans control relay & checking any fuse for the trans.

 

Ed

[Mopar1973Man]

Power is supplied for the Blue wire from Red/White wire 20A fuse. It most likely has some sort of switch action inside the PCM to cut the power when the key is off.

[milradioman]

I will check power to the pcm and fuse, and swap the trans relay.

[milradioman]

Ok, I swapped the transmission related relay in the fuse box (engine compartment) with the highbeam relay, checked the related fuse-good, still no change.

 

Looks like a new pcm.

[Ilikeoldfords]

Can you have a PCM reflashed at the dealer? I don't know if that would bring it back around or not though. I wonder if some noise off that alternator took out the PCM? I don't think they usually fail.

[Mopar1973Man]

Can you have a PCM reflashed at the dealer?

 

From what I've hear is yes. But you need a Dodge Dealer that knows what he's doing to make a proper flash occur. Most dealers techs can't even figure it out, sad to say...

[milradioman]

I cannot trust the local dealer with an oil change, and I don't have the time to dirve further to the next town to try them.

 

I am going to order a pcm and see what happens.

I found a site called Dodge PCM Direct, anybody have any experience with them or any other sources?

[milradioman]

Well, fixed the problem; My brother happens to work for a Dodge dealer in the service department, and just happened to be visiting this week, so he quickly ordered and brought a pcm, and his scan tool.

We did some testing and determined the problem is in the pcm, so we replaced it, after we started the vehicle we still had the same problems, after much head scratching we determined one of the outputs had shorted to ground and blew the pcm again.

He was about to order another pcm, but we looked at the system one more time, I noticed the blue field wire to the alternator (+12 v) appeared to short only when the engine is started, and ok while running, so we shut it off and checked continuity on the blue wire while moving the wire harness, we found the problem was the blue wire just happened to be on the outside of the wire bundle and about 1-1/2" of unprotected harness was rubbing on the painted oil dipstick tube and finally wore through the paint and the wire insulation and shorted causing the symptoms I noticed. The harness just lightly touched the metal so it only shorted when the engine torqued from starting, so we were not able to find it at first. Fortunately the pcm is not blown, but simply shut down due to the intermittent short. Apparently the pcm is a very reliable unit, the problem is caused by some outside source.

So, glad to have my truck running again!