Investigation: Was my PCM reprogrammed?

[Cadillac Jim]

Kevin - the post didn't say that a dealer could bypass the code; he said "it is possible..." rather than "the dealer can..." bypass the oxygen sensors. What that means, and the moderator explained that - possibly a bit too verbosely - as he went on that this requires replacing the code in the PCM. This just isn't something a dealer can do. As the moderator says, one would have to reverse-engineer the code in the PCM, write new code that did different things like ignore the oxygen sensors, and put it into the PCM - process that would mean removing and replacing surface-mount chips on a multi-layer PC board.

Something that people may believe is like that is done with aftermarket PCMs but not really. The factory PCM is actually several modules that are closely coupled, and the PCM is itself closely coupled with the spark module, yet another computer. The fuel injection, spark advance, emissions control, and parts of Stabilitrak, traction control, plus the speed governor and the rev limiter are all in the PCM module. The PCM takes commanded torque signals from the EBTCM as part of TCS and Stabilitrak, for example. Then, there's the OBD part of the module, which is itself two separate sets of requirements, functional and network/reporting. In aftermarket PCMs just control the fuel injection and a spark module. A separate module is used for controlling electronic transmissions, whereas in the factory GM PCM these functions interact and are integrated. OBD and network functions, OBD, etc. are usually not supported by aftermarket PCMs.

So, I interpret the moderator's comments as saying that it may be physically possible to modify a PCM for a car driven on the street to ignore the oxygen sensors, but that it's not likely anyone has ever done that, and that it's a vanishingly small likelihood that any dealer would be able to do that.

When you compare the idea of changing out the PCM to an illegal partly bogus one with just putting in dummy oxygen sensors, it's clear to me what they did.

As for the date of manufacture of the cat, get a mechanic's mirror and look all over it for any number or other identification that will give you a lot number or anything else that will identify it in any way. If it's lot number indicates that it was manufactured after your car was, then it was replaced. If it is as old as your car, it's very unlikely that it was changed.

[KHE]

As for the date of manufacture of the cat, get a mechanic's mirror and look all over it for any number or other identification that will give you a lot number or anything else that will identify it in any way. If it's lot number indicates that it was manufactured after your car was, then it was replaced. If it is as old as your car, it's very unlikely that it was changed.

That is what I was referring to in asking if there was a date code. If there was, MAC would know if it was replaced or not.

[MAC]

As for the date of manufacture of the cat, get a mechanic's mirror and look all over it for any number or other identification that will give you a lot number or anything else that will identify it in any way. If it's lot number indicates that it was manufactured after your car was, then it was replaced. If it is as old as your car, it's very unlikely that it was changed.

That is what I was referring to in asking if there was a date code. If there was, MAC would know if it was replaced or not.

This is good advice except I'm not sure if the converters will have a stamp. I Googled the topic and I couldn't find a definitive answer. I did come across an article stating California enacted a law effective January 1, 2009, which requires converters to have an identification stamp.

[Texas Jim]

As for the date of manufacture of the cat, get a mechanic's mirror and look all over it for any number or other identification that will give you a lot number or anything else that will identify it in any way. If it's lot number indicates that it was manufactured after your car was, then it was replaced. If it is as old as your car, it's very unlikely that it was changed.

That is what I was referring to in asking if there was a date code. If there was, MAC would know if it was replaced or not.

This is good advice except I'm not sure if the converters will have a stamp. I Googled the topic and I couldn't find a definitive answer. I did come across an article stating California enacted a law effective January 1, 2009, which requires converters to have an identification stamp.

One way to find out if yours has one is to go look at it...

[Cadillac Jim]

I would expect that if GM bought cats from an OEM supplier that they would want lot identifiers on them in case of problems and for parts tracking in repairs. If it doesn't have any markings at all, I would suspect that it isn't a GM part.

[MAC]

As for the date of manufacture of the cat, get a mechanic's mirror and look all over it for any number or other identification that will give you a lot number or anything else that will identify it in any way. If it's lot number indicates that it was manufactured after your car was, then it was replaced. If it is as old as your car, it's very unlikely that it was changed.

That is what I was referring to in asking if there was a date code. If there was, MAC would know if it was replaced or not.

This is good advice except I'm not sure if the converters will have a stamp. I Googled the topic and I couldn't find a definitive answer. I did come across an article stating California enacted a law effective January 1, 2009, which requires converters to have an identification stamp.

One way to find out if yours has one is to go look at it...

I'll take a look over the weekend to see if I can see anything. I'll check PepBoys for a mechanics mirror.

[MAC]

The key is That the dealer may be able to reprogram some parameters that throw a code and turn on the MIL but they cannot disable the oxygen sensors.

As for flames and flamers, I always repeat this mantra when I'm tempted to respond to one: Never wrestle with a pig; you both get dirty and the pig likes it.

Attached is a screenshot of what I saw when I tried to check O2 sensors. I'll try to check them again either tomorrow or Saturday. The scanner could see the sensors are 'Present' and detected both are in 'Closed Loop' but could not read any data, which makes me believe I will probably get the same results when I try to check them again.