Based on inmput from a previous thread, I was wondering if anyone has had issues with service visits due to the use of preprogrammed PCM's. I know from experience that the PCM (and probably other Control Modules) have some non-volatile memory that contain VIN, mileage and code history. Has anyone had issues with going in for service and being questioned about the mileage of the PCM not matching the odometer etc?

Nobody has ever said anything to me. Yet. PCM's are "married" to the vehicle, but do not track mileage that I'm aware of. When the computer need mileage info, the PCM requests it from the bus IIRC.

The reason I believe it does, is that I did a hopped up PCM swap on a Grand Prix GTP and the mileage and VIN from the previous vehicle always showed up. Luckily, I never had any sort of service done on it. Then, on my '05 Sierra when I took it into the dealer (after clearing codes with a Tech 2), the tech was able to tell me exactly what mileage and how many minutes into each start the codes were set. And like I said, they were cleared with a Tech 2 to the point when looking under code history, nothing showed up. I was really surprised he was able to tell that. I would hate to be on a trip across the country, where I have to replace my original PCM before I could tow it in to a dealer I do not have any relationship with. I may be a bit paranoid, but I am just trying to make an informed decision on what to buy. The TTS sounds good with a good level of satisfaction as far as most posts go.

Thanks for your help!

With respect to mileage, I looked at the Helms service manual schematics about a year ago. This is what I remember. There was a signal coming from the transmission that produced pulses for each output shaft rotation (for conversation assume one pulse per output shaft rotation). This signal goes to the ECM. The ECM applies a scale factor (to account for different tire sizes). The ECM outputs a "normalized" pulse rate to the instrument control panel and the BCM (body control module). Example XX pulses per second = XX MPH. So at least 3 electronic devices within the vehicle have the "capability" to see the vehicle speed. If each of these devices is accumulating the number of pulses over time, you have total mileage.

In our vehicles, there are a number of controllers that are networked together. You would need the detailed software interface design specs in order to determine what the message flows are between these units and some description of the controller code in order to determined what is stored locally within each controller. GM could make it really interesting if they wanted to.

They can perform diagnostics on it......I took mine in and he had no problem. But they probably will be able to tell something is up. And the tech wont be able to reflash the brain. This is a good thing though since if I took my truck in for a free oil change and a tech trying to be a nice guy mentioned he did a updated flash while he had it in I would probably develope a tick and a throbing vein in my neck:banghead::nutkick:

mileage isn't stored in the PCM so you don't ahve to worry from that standpoint.

So what exactly is stored in the ecm? :confused: Is the mileage or vin # stored in it? I have seen several posts from different people that don't agree. I am very nervous about the whole odometer mileage not matching the ecm mileage issue. When I sell this truck and have to sign the odometer certification paper I don't want to go to jail if they don't match.

if you're nervous call and ask them. mileage isn't stored in the PCM. the VIN in. mileage is stored in the cluster. just ask anyone with an Escalade cluster.

Diesel power is right, when you send out a IPC for repair or replacement they need to know your mileage. If you go into the shop and your PCM is shot, when I install a new one and program it, it gets the calibration info straight from TIS and doesn't ask for mileage. The only thing a PCM can store related to mileage is miles since DTC set.

I would always swap back to the factory ecm.................kinda like now..........Its been a long service call

da power wrote"The TTS sounds good with a good level of satisfaction as far as most posts go."

It is truly is great programing but It comes at a cost, namely a second ecm for most and due to steves other distractions the wait can be rather lenghty

Damn those distractions! ):h ):h ):h :grd: