Engine/Transmission (1994 - 1998) replace PCM & maybe relocate PCM

[bd450]

After much troubleshooting with OBDII scanner, pressure gauge, DVM, replacement pressure soleniod & sensor I've come to the conclusion that the gov pressure soleniod output in my PCM is bad. Probably the output stage transistor but haven't looked inside the PCM yet to see of the transistor is replaceable.



Question #1 is... Does anyone know of a souce for PCMs? I called Longhorn Dodge allready about a rebuild. Was wondering if there is anyone else that sells discounted PCMs?



Question #2 is... Does anyone know of a souce for male and female mating connectors that the PCM uses?



I'd like to relocate the replaced/fixed PCM into the passenger compartment where it belongs in the 1st place. Underhood heat is definitley not good for electronics. Can't understand why Dodge put it there in the 1st place (lazy or cheap or both!?). Especially, with a very hot turbo nearby.



Listen up DODGE engineers! My 17 year old 200+Kmi, Toyota 4Runner has it behind the passenger kick panel. When/If Toyota make a 3/4T TD I'm there!



TDR members, sorry for the vent but after; crappy Torque converters, KDPs, Fuel return lines, Fuel gauges, starter solenoids, etc, etc. I'm starting to get a little fed up!



BTW, I'm an I. C. engineer so diggin into the guts of the PCM is no big deal.



Any help finding these parts would be appreciated. Thanks

 

[illflem]

Never heard of a gov pressure solenoid. Are you talking about a 24 valve?

 

[bd450]

47RE auto trans (behind a 12V). The governor pressure is controlled by the PCM via the gov pressure solenoid in the valve body. Should be ~1psi per 1mph road speed.



My PCM is bad and I get 75psi at 0mph. Checked tons of stuff, Ohmed out wiring, replaced solenoid & sensor, fiddled with a zillion sensor resistors. Finally grounded the solenoid thru a 12ohm 10W resistor and got the pressure to drop down to 20psi.

(like the PCM should do if it its output transistor (i think) wasn't bad). I get a OBDII code that says "pressure ckt A electrical fault" or something to that effect. 95% sure the PCM is bad.

 

[illflem]

Whoops, forgot all about that one. Was thinking of engines, not trans.

 

[Todd T]

you should be able to find a PCM at most of the larger chain store auto parts places. much cheaper than the stealer would sell them.



connectors are a different story. Ace electric and Columbus Kansas comes to mind. but maybe not, give them a call it couldnt hurt.

 

[Swamp Donkey]

I have gone through everything you have bd450. Resistors, governor pressure solenoids, valve bodies, overdrive solenoid, pressure testing in every port, more voltage reading and testing and transmission pan droppings than I like to do. It has actually been quite the ongoing saga for a couple of months. Bill K has been extremely helpfull. He sent me a new valve body to try, at his own expense. That did not work. He finally sent me a PCM also at his own expense to try. It was my problem. Only it was a PCM from a 97 so none of my gauges worked but my transmission shifted correctly. Bill has gotten me a new PCM for less than the stealers. You may want to try Bill (DTT) for a PCM. 1-866-504-4002. Tell him Swamp Donkey sent ya for a PCM!





One more thing... ... ..... I don't know very much at all about electronics, but did you mess around with the light green and white wire pin#29? Everyone concentrates on the orange wire pin # 31 but the #29 is intriguing to me. I don't have my FSM in front of me, but I thought I could manipulate the voltage up or down to fool the PCM governor pressure solenoid. I will try to contact you later when I have more time and my FSM.



On edit: I also had the PCM reflashed at the stealers..... to no avail. Just lightened my wallet by 35 bucks.

 

[bd450]

Swampy,



Did you ever put a OBDII code reader on your PCM?



I'm going to pull the PCM this weekend an have a look inside to see if the gov solenoid driver has a repairable output stage (i. e. a transistor I can find a replacement for and replace).



I'm a circuit designer so as long as it isn't buried inside some impossible to obtain chip is should (eventually) figure out some was to fix it or work around it. The fact that someone sells rebuilt PCMs makes me think there's hope to fixing mine.



If I figure it out and fix it maybe you can send yours down. I'd do the same fix for nuthin but shipping. Glad to help out another dodge sucker..... er I mean owner.

 

[Swamp Donkey]

bd450,



No I have never put a OBDII code reader on my truck. I sure would be interested and take you up on your kind offer if you find a fix. I kinda poked at my PCM but did not wan't to break anything when trying to take it apart. The service guy at our local Dodge stealership said you can take them apart and shoud be able to visably see the fried part. Where were you about 4 month's ago? LOL. I am a procrastinator extrodinair.





Please keep me informed.







John.

 

[bd450]

Swampy,



I'm just as bad. I get maybe 2-3 hrs a week to work on the truck. Something like this takes months to fix, but with so little free time I refuse to let it cut in on my allready limited MX riding time. Ain't got that many years left to do that. Can tinker with trucks for a lot more years.



Anyway, I'm going to pull the PCM this Sat and have a look inside.



Depending on the way things like this fail there's only a fair chance you'll be able to see burned parts. Plus when that happens theres a good chance the circuit board is damaged too. Thats pretty tough to repair unless you have a schematic.



I'll let ya know what I find.



Brian

 

[CPG]

Originally posted by bd450

Swampy,



Did you ever put a OBDII code reader on your PCM?



I'm going to pull the PCM this weekend an have a look inside to see if the gov solenoid driver has a repairable output stage (i. e. a transistor I can find a replacement for and replace).



I'm a circuit designer so as long as it isn't buried inside some impossible to obtain chip is should (eventually) figure out some was to fix it or work around it. The fact that someone sells rebuilt PCMs makes me think there's hope to fixing mine.



If I figure it out and fix it maybe you can send yours down. I'd do the same fix for nuthin but shipping. Glad to help out another dodge sucker..... er I mean owner.

 

[Swamp Donkey]

bd450,





How did you make out? Inquiring minds want to know!

 

[bd450]

Got inside the PCM yesterday and found the govenor solenoid driver transistor. It showed some faint signs of overheating. And turned out to be shorted gate-drain and open drain-source. Please, don't ask me to explain if you don't know what I'm talking about. That would take a short course on semiconductor theory. Just suffice it to say the transistor is bad. Appears the upstream driver of this transistor is ok. I checked the ouput with my o-scope.



Then I carefully scraped the sealant coating off the transistor and found the numbers but have not been sucessful locating that P/N. It appears to be a motorola part or maybe a mitsubishi. Hard to tell the difference in their "M" logos when they get that small. Checked both web sites but couldn't find the transistor listed. I believe motorola sold their discrete transistor buisness a while back and can't remember who they sold it to.



From what I was able to deduce of the of the driver circuit and knowing the transistor is supposed to pull up to an amp thru the governor soleniod (by pulse width modulation I believe) I ordered some transistors from International Rectifer that will hopefully work in this application. I'll keep trying to find the OEM part in the mean time while I'm waiting for the IR parts to arrive.



I shut the PCM back up and stuck it back in my truck so I can at

least haul my bike around. Will probably get back in and put a new transistor in next weekend (assuming they get here by then).



BTW, I used to run a mystery switch and jumper instead of the trans relay. After seeing how this ckt operates I doubt I'll ever run without the trans control relay again.



Swampy, were you running a mystery switch and jumper instead of the trans control relay?



If I had a schematic and parts list of the PCM I'll bet I could fix just about any PCM internal problem. They are definitely servicable. Trying to fix these kinda of things without the documentation is pretty tough.

 

[Swamp Donkey]

Yes, I am running the 3 positon mystery switch with the jumper instead of the relay. You think that is what fried my PCM? If so... ... . I will disconnect it soon. I really like the unlock feature though. That is great news that they are serviceable. Unfortunately I just bought a new one last week. I am having the new one installed on tuesday. The Stealership has install or program a serial number into it. Then I am good to go.



I will still send you my PCM for repair... ... ... because it is obvious these things are not bulletproof. That is if the offer still stands of you repairing mine. Postage + a little extra for your time is still one heck of a deal! Thanks.

 

[illflem]

Before you send it off... Not sure about the stealer but Napa gives you a $250 core refund on the PCM. That indicates to me that they are rebuildable.

Also schematics should be available before too long, a law was passed recently that prohibits auto/engine manufactures from keeping repairable electronic circuitry secret.

 

[Swamp Donkey]

I never even tried NAPA. Oh well. I got one from Bill and it is going in tommorow. Next time I will know better!

 

[bd450]

Swampy,



All I can tell you about the mystery switch is that if you replace the trans relay with a jumper to use your switch then +12v power is applied to the gov pressure solenoid allways. Whereas with the relay in place the PCM can choose to power/de-power those ckts. Maybe the relay is just there to depower the ckts in case a fault is detected. Or maybe it also delays powering up those ckts at startup for some reason.



It could be an isolated failure that my transistor blew and yours did too (assuming your failure is really the same as mine) or maybe its some how related to a rare event that can happen when the jumper is in place. I've not heard of others having the same problems but I'm going without my mystery switch & jumper for a while after I get this PCM working again. Maybe after 3-6 months of satisfactory operation I may try the mystery switch again. That way if it blows out the transistor again I'll have a good cause & effect link.

 

[fest3er]

Circle-M (Motorola) sold off their commodity semiconductor business to OnSemi.

 

[bd450]

Thanks Fest3er.....



It is an old MOT part. Got later generation replacements on the way... ...



Man I hope this fixes the sucka.

 

[bd450]

ITS FIXED! Oo.





That transistor was the problem. Shifts are completely normal now.



Going to look into building a heat shield for the PCM or maybe a turbo blanket and header wrap on the down pipe.





Swampy, did you get your new PCM in? Does it work? PM me if you want me to look at your old one.

 

[troutlips]

Can you tell me the nomenclature of the mosfet for the governor on the PCM? Sound like it is conformal coated. My son's truck is showing the same failures.



Any new information on exchanging PCM's or who rebuilds them? thanks