The 52 Dodge truck I just built has a 5.2 out of a 97 Van with a 42re trans. History on the 42re is unknown. It keeps throwing a PO500 code, VSS signal. I replaced the VSS. It's a three wire Hall effect VSS. Traced all the wiring all is good. One of the things I read that can cause a PO500 code is tires are miss matched to the PCM. I'm not sure what the PCM is out off because it's a reman PCM. I have 245/70/17 tires on the back, 30.5 inch dia. The tag on the rear end says 2.9, so I'm assuming it's a 2.92 ratio. I can erase the code and the truck will drive fine for 10 to 20 miles then throw the code again. I'm wondering if I went to a smaller tire or a lower rear ratio, like a 3.55 or 3.90 it the problem will go away. Any thoughts on this or has anyone ever heard of miss matched tires/ PCM causing a PO500 code?

does "mismatched" refer to a front/rear size difference or maybe a roll out difference on the rears only ?

Mismatch refers to tire diameter. PCM expects to see a certain engine rpm at a certain road speed, within a certain tolerance.

You need to match the tire diameter to the PCM donor or get the computer reprogrammed to account for the new tire size. Assuming a 97 1/2ton van it's a 29" tire, P235/75R15. What are you running?

Thanks, that's what I thought. Since the PCM is a reman, I don't know what vehicle it came out of. I have 245/70/17 tires on the rear. 30.5 inch dia. The VSS is in the trans tail shaft, no ABS on the truck, so all the PCM is seeing is the trans out put speed vers engine speed. Changing tire size or gear ratio doesn't change that relationship.

got it now. thanks !

The tire programming on all the Mopars I remember when I worked at the dealer in the 90's up to 2010 was all done in the Anti-Lock Brake module. I forgot what year but they started using the ABS sensor in the rear diff for the speedo also and we had to program tire size in the ABS module. They had a selection of sizes and if the size you had was not in there you could also program it in by "Revolutions per Mile". I dont remember the PCM's having any option to program tire size but we did program some Trans modules on front wheel drive with what was called "Pinion Factor". But again that was in the TCM (trans Control Module). I have been out of its since 2011 but I dont remember any options in the PCM's for programing tire size as it was done in the ABS or trans module and then that info was bussed to the PCM. Ron

Also the 42RE has an electronic Gov so it has a speed sensor in the trans tail housing but that is not for the speedo as thats so the TCM/PCM can know the driveshaft speed so it knows where to set the gov pressure at as its not for vehicle speed just driveshaft speed. If that sensor goes bad the trans wont shift right since it wont know driveshaft/roadspeed which it needs to know to duty cycle the gov solenoid to set gov pressure. Ron

Ron, I think you are on the right track. I believe this thing is throwing the PO500 VSS signal code because it's not getting a VSS signal from the ABS module. Quess l need to visit the dealer and see if they can help. I need to get this fixed before I sell the truck.