PCM Mileage Inconsistency

Hello all, We have recently purchased a 02 996 C2 from an OPC. Our first Porsche and it's superb. The car was sold to us with ~18,500 miles on the clock, which seems to be verified by the history. However, when playing around with the PCM the other day I noticed the 'continued' trip computer details shows a mileage of 24,500. Can anyone explain this? The OPC said "have you tried resetting it?", but surely this will just put it back to zero and hide it? Any help much appreciated. Thanks N

Resetting it will just zero the counter, yes. Might be worth asking Porsche GB Reading to confirm whether it is possible for PCM ever to show a mileage greater than the car's actual mileage. I can't think of any way, offhand (which means nothing!).

Thanks guys. We're taking it to the OPC on Saturday for an investigation/explanation. What worries me more than the value is the fact that there's 6000 miles that are unaccounted for in the history. Will let you know the outcome. N

Already thought of that!

What happened on Saturday?

Before we went I phoned Porsche GB in Reading - they thought it very strange and suggested we took it to the OPC. The OPC reset the PCM (!), took the car out and did a few miles - apparently the PCM differed from the speedo by 0.2 miles in about 5. They told us the PCM and the clock get their readings from different places (the sat nav system and the wheels respectively) and that, whilst they didn't think there was anything wrong with it, if the problem continued they could re-calibrate it. I wasn't entirely convinced, but we decided to take their word for it and leave it at that, knowing that I could keep an eye on it and still go back if necessary. Anyway, we took the car home which is about 40 miles, and the two were perfectly in sync all the way. The more I thought about it the more I think we were fobbed off - 6000 miles in 18,500 hardly sounds like a calibration problem! So we'll be calling them again today.... N

0.2 miles in 5 = 4% 6000 miles in 18500 = 32.43% That is some difference in callibration error!

Well at least your odometer is reading the lesser of the two mileages and you can always get the PCM reset again prior to selling the car. A milage discrepancy of this scale could arouse the suspicion that you have and put off any potential buyer. If the sat nav calculated milage is actually the correct one, then maybe that's not a bad thing in respect of resale value!

UPDATE: Spoke to Porsche GB again - they have told the OPC that they need to get the car back in and 'take some more readings'. Things very busy for the next couple of weeks, so they are collecting on 6th April. N

Hi, I have PCM* in a boxster and carrera-both mileages correspond. They also have a new tyre calibration so I assume its checks between the two. Sounds fishy too me. *PCM2's

Just a thought, maybe one reading is set for MPH & the other KPH - that would account for the difference. I have a 996 with PCM and will monitor the two readings - at the moment they are perfectly in sync and thought (logically) they would take the mileage from the same source. They satnav and BC (computer are seperate but related functions)

Don't talk to me about miles and kilometers!! I have just had the biggest nightmare with our other car. The gearbox went on our Jeep Grand Cherokee which had covered 50,000 miles. The dealer said their diagnostic machine indicated it had really done 80,000 miles and had therefore been clocked, so it wasn't covered under warranty and they would like £4500 for the job. Anyway, loooong story but I finally proved that the 80,000 was in fact kilometers! I was sure that wasn't the case with the Porsche though, as the PCM does say miles, but you've got me wondering now.... N