Great Forum!
I want to describe my problem and chronicle my repairs for the readers. I have been through 29 pages of 2nd Gen Ram as well as a general search and found the PCM/ECM posts helpful, but I am not sure they fit my situation.
1996 Dodge Ram 1500 4X4, Auto. 178,000 miles, 5.2/318.

First symptom was a synthetic sour odor in the cab with or without the heat on. It smelled almost like hot antifreeze but with an electrical synthetic quality. The truck continued to function and threw no code so I ignored the smell.

I recently had the transmission rebuilt as a separate matter. (it was on the fritz so I also thought the smell could be coming from a bad bering getting hot) Check engine light was on after trans. work (forgot the code) so the mechanic recommended that I change the old plugs and wires since they were "arc-ing". Did that.

Next, battery is dead. Put a full charge on it and truck ran fine. Battery dies again. Yanked the alternator, tested it, bad alternator, replaced it. Smell persist.
Driving at night with power loaded, lights, radio, heat, the headlights start to flicker, the engine sputters, and the "Gen" light comes on. I'm able to make it home by keeping the throttle on at stops. I pulled the code and I believe it is one of these from the code index:
P0621 Generator Lamp "L" Control Circuit Malfunction
P0622 Generator Field "F" Control Circuit Malfunction

I believe that my Alt. and Batt. are fine but for some reason, the power is not circulating to maintain the charge and keep the engine going. For instance today, we jumped started the truck but as soon as we took the cables off the other vehicle, my truck died; however, the meter gauge for electric is strong around 16.

I can get a refurbished Cordon for $265--they will flash it with my VIN #s. It seems that I have a chicken and egg problem in that I'm not sure if the bad alt. fried the PCM or the bad PCM ruined my Alt. or a low battery did it to both. I also use jumper cables frequently to assist my tractor starts in the winter and that could do it too.

If anyone has been through this process and wish to tell me that I'm an idiot and just need to brush up my battery terminals, please do. These trial-and-error/process-of-eliminations are expensive but not as much as the Dealership.

Sorry for the long post but I wanted to set it for the analysts on the forum.

 

I really don't have to know how like others do to help. But maybe I can jump start thread for you. Had my ECM just replaced after going through many sensor swaps and cleanings. My situation was only present when temps dropper to 30 and below for long hours. Use heater to coolant overnight and van would start. Use space heater in mornings pointed at engine and van would start. Finally it was suggestion to me to use a hair dryer on my ECM to see if van would start. It worked. So after lots of time wasted on sensor and testing and asking for more advice I swapped out old for new ECM and Cold weather problems are gone. Never had spark or fuel pressure when temps dropped but now I had both. Key word was HAD. No sooner I fixed that or while ECM was on order fuel pressure is now gone. Though it was related but isn't, as far I know right now. But van will barely start only for seconds. Just 6psi coming out of fuel line.

So anyway my point for you was that the ECM does do crazy things to other parts of the system. Seems one things related to the other and the other and so on at times. Best of luck.

 

Thanks Bert, I read your post earlier. The control module, from my limited knowledge, basically runs the whole show so if its not happy you're done.

I am interested to know if anyone else has experienced the sour odor when their module was failing. I would hate to replace it and find out that it's a fuse or ground. I will follow-up.

 

I replaced the PCM last night and it resolved the problem. I installed an AC Cordon pre-flashed module and three screws and three plug-ins later and it fired right up no problem. I wish there were a way to find out what caused the old one to go bad but may they will know when they test the old core at the re-manufacturer.

 

Nice Sheltie. I have 3 Shelties, a collie, and a long haired dachshund :P

 

She loves to ride and bark at the cows.

 

where did you get your ecm or pcm? im pretty sure its my pcm exact same problems, had many different test run, had all wires checked, nothing everything is fine, and it happened out of the blue one night when i was driving. it decided that it was time to retire i guess. looking for a good price on one, do they have to be pre programmed?

 

Autozone by me (mukwonago WI) sells them for 190-210 bucks

 

What happened in this case was due to a failure at the PCM specifically, a failure with both the VOLTAGE REGULATOR (16V is approaching the upper limit) and, a failure within the FIELD and SOURCE at the PCM thus, unable to conduct DC current to the BAT.

CM

 

Hey Yall, my two cents worth for people who see this later... A bad PCM wont necessarily be the cause of too many volts... I have a bad alternator cause the voltage so peak at 20V (no kidding, burned the battery, I wont tell the story...), and a bad wiring harness has caused the PCM to get confused and output 18 volts in another case... Also, if the voltage regulator in the PCM has gone bad, you dont have to replace the whole PCM if just the voltage regulator has gone bad. You can rig up a reliable regulator external of the PCM for about $30. If done right, you can fool the PCM to think everything is fine. You can then intercept the connection to the GEN light and hook it to your external regulator so it still will turn on the GEN light if a problem occurs. Hope this helps! --Keagan