Little backstory... Dakota 3.9 4x4 coming out of a 3 year stent in the garage. Rebuilt engine, re-manufactured transmission, lift kit, tires. I'm in the process of getting her ready for the street, but it seems like each day I go out to the garage, I have a new electrical problem to figure out. Yesterday, the red check gauges light came on and my alternator gauge was at 8v so I went to bed thinking my good yesterday alternator died in the garage somehow. Today, my overdrive light randomly came on and will not go off no matter how many times I press the switch. Two days ago, with the truck idling in the shade, the check gauges light came on as the coolant temp went up to like 260 and was kind of bouncing slowly around. Keep in mind I have a 190* thermostat installed. A week ago the speedometer wasn't working but then decided to start working again...Oh yea and the trans is not upshifting at all...

My question is how to diagnose a bad pcm and if mine is actually bad? With all these components working fine before the rebuild, I'm very suspicious that they all are not working now. The funniest thing about it all is I do not have a check engine light on...

 

I sure hope the engine did not in fact see 260. O/D off usually only comes on with the trans temp light, the converter locks up to decrease heat and trans goes 1:1 to bring engine RPM up to increase trans pump speed to move more fluid through the cooler.

Definitely some suspicions going on....

 

I just walked out to the truck to double check that temp reading. It was more around 220F (last white band). I'm just stumped. If it was one or two electrical issues that would be one thing but 4 to 5 has me thinking pcm. And there's the fact I'm not getting check engine lights.

When I initially went to start the engine, I was getting a no start. The auto-shutdown fuse was blown. 30 amp if I recall. There was a possibility of when we were laying out the wires, something must have connected to blow that fuse. The engine ran fine before the truck went into the garage. I guess my question is can the truck partially run with a damaged pcm? Also, does the dealer have something that can diagnose this better that just a scan tool looking for codes? I hate throwing parts at a problem

 

Diagnosing a bad PCM is more eliminating any other possibilities..... There is only one code the indicates a bad PCM for sure...... and that is just a rom checksum error.....

Think I would go after grounds first, and see if that made any difference.

 

I won't be in OKC any time soon, my DRB3 would be the closest thing around (it's the original dealer tool).

Bad grounds is a valid suggestion, I've experienced wierd behaviors with grounds. Also, you say you're not getting codes, are you able to scan pending codes? That might give you more information.

I'm curious how you shorted the ASD relay. That would take some talent....

 

what is a drb3??

 

Chryslers high-zoot scan tool.

 

Well this morning I went out and expected to put the key in a find a new electrical problem. I had it on the trickle charger since yesterday so I decided to drive it up to the corner store to finally get some good gas in the tank. Had to take a couple neighborhood back roads because I only had first gear. Get the gas and on the way back out of no where it shifted gears! It threw a trouble code right when it shifted. I made it home and put the code reader on it and got P0720. Output speed sensor. I replaced both of those the other day.

Another back story... When I first got the truck I took it off road and one day got a net wrapped around my rear drive shaft. When I got home my moms boyfriend was super eager to help and went freddy krueger on the net and in the process cut my output speed sensor wires. He felt real bad and confessed to having very poor eyesight, which I did not know. I wound up crimping the wires back together and putting shrink wrap around them. It worked fine for a couple of years until the truck went down. I'm thinking possibly one of those is not the best connection and I might need to solder them. I am still concerned about the PCM though

 

yes, speed sensor wires need to be soldered and heatshrinked. JTEC is very sensitive to voltage out of range or out of sync. Alot of people have issues with crimped wires. One of the connections may be corroded now. I like using adhesive-lined heatshrink to make a water resistant connection, but it's very hard to find - usually used in aviation and military.

 

Ok thanks for the heads up. I'm definitely going to have to take care of that. The alternator has to be going or out. I made it back home to a dead battery. It sounds like one of its bearings is gone. I'm just super happy the truck is shifting gears