The Devil's Dodge

Ok, I've got one for ya. I'm working on an 02 dodge 2500 4x4 with an 8.0l V10. The symptom is that the "trans temp" light and "od off" light come on and the truck has no od. Checking with my S.O. Verus the ecm had no codes (trans or engine). Checking the trans temp pid data when the truck is sitting cold the trans temp is usually about 125 deg, though it does fluctuate up and down at times. If you drive the truck the temp increases to well over 250 degrees and the lights come on. The trans temp sensor reads the correct resistance for the temp I expect the fluid to be when tested at the ecm. The wiring is good as I ran new wires between the sensor and ecm, soldered with weather pak shrink tubing to be sure. The lights still come on, no codes, still shows it's too hot in the scan data. I removed the ecm and sent it to Solo Electronics. They said it was fine. Did a solder joint refresh and sent it back. Still did the same thing. Temp sensor resistance fine, scan data shows it's much hotter than it is. I removed the wiring to the sensor and back probed my Aeswave variable resistor (set with my vantage at 2k ohms, about 78deg) into the ecm and the scan data showed it was about 140 degrees. I know the ecm is toast. If I measure the voltage exiting the computer on the wire between the resistor and the ecm it consistently reads .5-1.0v different from what the scan data shows. If I briefly ground it the Vantage reads 0.00v and the scan data reads .47v.

The ecm for this truck is total unobtainium. I may as well be looking for parts for a DeSoto. After a back and forth with Solo electronics they said they didn't think they could fix it. I did find 2 available on car-part.com and was able to procure one of them. After installing that ecm the trans temp operated perfectly. I was able to drive the truck and it operated exactly as expected. However, the truck doesn't charge and sets a code for it. Plug the old ecm back in and it charges just peachy.

My questions are, is it possible something cooked the new/used computer when I plugged it in? I've been doing this a long time and don't suspect so since it's a totally different problem. I'm using a used part of unknown origin, so that's what I'm thinking is causing it, but I wanted to bounce it off you folks to see if there's anything else I should check. Battery/engine/frame grounds are all tested and good. I also load tested the power/ground circuits that power the ecm and all are good.

Is it possible that there is a programming issue? There are no programming issue or anti-theft codes being stored. The key doesn't have a chip. The ecm I got had the same part number and other than the charging issue seems fine otherwise. I'd find it hard to believe the truck it came from didn't have that feature. What do you think?

My next question, which I also asked in the "auto parts" section of the forum, is who's the super ScannerDanner ecm magician? Does anyone have a really good rebuilder they could recommend? I think a lot of these places can repair bad 5v regulators, resistors and drivers but when it comes to a problem like the first ecm, where it seems like the cpu went haywire or there's some stray voltage on the board somewhere like a tin whisker or something most of these places are lost. I think the used ecm will be rebuildable but I want to make sure I'm not chasing my tail here.

Also, the truck skates any emissions nonsense where we live so I'm not concerned about the check engine light being on so if anyone has any ideas on how to bypass the smart charge system with a regular alternator or any other way that would work I'd be down for that too. Actually, I'd be down for just about anything that would get my customer his truck back and me paid at this point.

Thanks,
Nick

Hey Nick!

I tend to think that you fixed one problem and install another with the used module. I doubt it was anything you caused during the swap, and you've proven the wiring and alternator are capable of charging.

If it were me, I'd still check the field control wires at the alternator, just so I know exactly what we're missing. If you haven't already, I'd also check codes in the replacement PCM, and have a quick look at scan data while it's not charging. Looking for what the PCM sees for battery voltage, battery temperature, and its alternator field percentage.

I can't say if it's a programming issue or not? :huh: But I did have a quick look at the charging system diagrams for the 5.9L gas, 5.9L diesel and 8.0L engines. They all use the same pins on the PCM for field control. That makes me suspect programming won't change anything.

As for bypassing the existing charging system, I've heard it can be done, but never done it personally. The alternator field is controlled by pulse width grounding the dark green wire. More ground, more current, higher charging rate. In theory, an external voltage regulator that does the same would work. Service info suggests the resistance of the field coil in the alternator is supposed to be more than .5 ohms, but less than 15 ohms. :silly: So I'd make sure that the external regulator can handle 2-3 amps.

Tyler wrote: If it were me, I'd still check the field control wires at the alternator, just so I know exactly what we're missing. If you haven't already, I'd also check codes in the replacement PCM, and have a quick look at scan data while it's not charging. Looking for what the PCM sees for battery voltage, battery temperature, and it's alternator field percentage.

I can't say if it's a programming issue or not? :huh: But I did have a quick look at the charging system diagrams for the 5.9L gas, 5.9L diesel and 8.0L engines. They all use the same pins on the PCM for field control. That makes me suspect programming won't change anything.

Agreed on checking to see what the field control is missing. On some Dodges around that MY the PCM supplies Gen Source and others field voltage comes from somewhere else. So if the replacement PCM isn't providing Gen Source it could be because it's programmed for a different MY.

Could also try reading the VIN from that PCM with a scan tool to see what MY it's programmed for.

support.alldata.com/alldata-repair-onlin...le/vin-to-year-chart

Yay! The Devil's Dodge lives and was returned to the customer! I wound up using a regulator kit I found on Ebay to control the alternator separate from the ecm.
A quick note. If anyone needs to bypass one of these ecm charging systems I recommend an adjustable regulator and I also recommend using the large lug off the back of the alternator as the field power wire with a relay to interrupt it when the key is off. I had a lot of problems with the truck lights flickering when I wired it any other way.

Thanks all for the suggestions.