Engine/Transmission (1998.5 - 2002) spare PCM question

[BJonesUSA]

Does anyone know if I can use a PCM from an '01 auto as an emergency spare for my '02 6spd? Trying to put together a stash of spare computers for my truck before they are too hard to find. TIA

 

[JLandry]

I'm guessing it would work in an emergency. The engine would most certainly run and you could drive the truck, but you may have strange behavior from the cruise control (if it even worked at all). You'd likely also get DTC's set because the VIN and mileage stored in the PCM wouldn't match the airbag and ABS modules.



John L.

 

[Gary - K7GLD]

For a perfect replacement match, as I understand it, ANY replacement PCM would require dealer reprogramming to match up properly with your specific vehicle - and then the trick is finding a capable dealership to do it, and at a price anywhere near reasonable.



I've been on the lookout for a PCM spare for my '02 6-speed too - but prefer to get as close to my own year and transmission setup as possible - dunno if the A/T vs manual transmission difference is a deal-breaker for match-up or not...

 

[JLandry]

For a perfect replacement match, as I understand it, ANY replacement PCM would require dealer reprogramming to match up properly with your specific vehicle - and then the trick is finding a capable dealership to do it, and at a price anywhere near reasonable.

I've been on the lookout for a PCM spare for my '02 6-speed too - but prefer to get as close to my own year and transmission setup as possible - dunno if the A/T vs manual transmission difference is a deal-breaker for match-up or not...

Gary,

Here's what I've learned about ECM and PCM compatibility from reading everything I've been able to get my hands on, and by poking around on Chrysler's TechAuthority web site. I know you know much of this already, so this is for the sake of others.

For some time now Chrysler has supplied a single generic Cummins ECM which must be flash programmed for the particular engine / truck application before first use. Once a flash file has been uploaded to a generic Cummins ECM using a Chrysler DRBIII scan tool (which is what a dealer would use), the DRBIII will refuse to re-program it to a different engine / truck application afterwards. However, the DRBIII will allow upgrading of an ECM or PCM flash file to a higher software revision level of the same application. This restriction is a safety measure put in place to prevent a mechanic from accidentally uploading a completely wrong flash file into an ECM or PCM. You can imagine the potential damage that could be done if this were to happen. On the other hand, it takes a special bench-mounted system to either change the flash file application in an ECM or or PCM, or to re-flash a Cummins ECM back to a generic software revision. Presumably places like Auto Computer Exchange down in Florida have this kind of equipment.

When it comes to a PCM, Chrysler still sells a specific one for each year and model. They don't sell a generic PCM the same way they do with the Cummins ECM. When you look at the flash file listings Chrysler has available on TechAuthority, you'll always see one available for each year and model application equipped with a Cummins ECM, but not always for a particular year and model PCM. I'm guessing this this is because not all PCM's have needed a software update since being released from the factory, and since Chrysler sells PCM's already pre-programmed, no release of the original software is needed.

In any case, no matter which flash file is loaded into an ECM or PCM, the ECM always needs the proper VIN programmed into it and the PCM always needs both the VIN and mileage programmed into it using a DRBIII. If this is not done, DTC's will be set when there are mismatches.

All this is why we have to be extra careful about trying to swap around ECM's and PCM's. Even if we had the appropriate bench system for reprogramming (they are available for purchase), we still wouldn't have access to some of the original version PCM flash files because Chrysler hasn't made them available to the public.

Best regards,

John L.

 

[BJonesUSA]

I'm not too concerned about throwing DTC's or not having CC, as this is a worst-case scenario where I would even use the spare, so as long as the truck will run, that's all I need.



On a related note, if an '01 auto PCM will work in my 02 6spd, what about an '01 auto ECM?

 

[JLandry]

On a related note, if an '01 auto PCM will work in my 02 6spd, what about an '01 auto ECM?

I think I've read here in the TDR forums where someone has put the wrong Cummins ECM in a particular vehicle such as you've asked about, and nothing harmful happened. The engine ran, but as I recall the wait-to-start light didn't quite work right, which I presume meant the grid heaters weren't working either. There might have been one or two other minor problems.



John L.