Thread: 2005 Grand Prix V6 3.8L displaying ERROR MI

Mornin! New here. 2005 Grand Prix displaying ERROR MI on the DIC. Check engine light was on and I had P0030 and P0420 errors as well. I started with replacing the downstream O2 sensor, then the upstream, and finally the catalytic converter w/both gaskets. I was finally able to clear the codes without them coming back after installing the new cat and the check engine light hasn't come back on but the ERROR MI message is still displayed. Any ideas on what else I could look for? My MPG has gone to s**t and it's driving more like my wife's old 4 cylinder Vibe. No power!

Do all your gauges go out in your cluster too. expect your speedo? Cuz kinda sounds like wat mine is doing

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No, everything else seems to be working/displaying fine. The only thing not working is the odometer (trip meters as well). They just say ERROR MI. What is yours doing?

My tcs turns off along with my tac, fuel level n temp gauge plus my areoforce n its saids error miles....but my seedo still works

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Huh! That's a lot of stuff going out at once. Have you run a code reader on it yet? I've had two different occasions where I've had to replace a wheel hub assembly, one on the front and one on the back, because the built in speed sensors were damaged. That caused the TCS and ABS to not work. But my 05 Grand Prix is just the base model so I don't have all of those other bells and whistles that your GTP has. Swing by your local autoparts store and ask to borrow their code reader. That should give you some idea. Let me know. Still haven't figured out my issue yet.

Sounds good

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Well the code said lost communication with pcm

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Hmm. Are you still having all of those issues or is the code displayed as 'History' on the scanner? If it's labeled 'history' on the scanner, that means that whatever was wrong has fixed itself (not really fixed, probably a loose connection somewhere that is currently not loose). But if you're still having all of those issues, I'd start by checking the connectors to the PCM. The PCM is located under the air filter box. The easiest way to take off the air box is to remove that stabilizing bracket (the one that's about 2+ ft long diagonal over the air box), then retract the two screws on the front end of the air box far enough to allow the box to be pulled out but don't remove them completely. Then disconnect the sensor from that big fat air hose (remove the white clip first), then loosen the metal clamp, pull the air hose off from the air box assembly and the entire assembly will pull straight up and out. It sounds like a lot to do but it'll only take a few minutes total. Plus it saves you from having to take the air filter out and putting it back in, which is a pain in the ass on these Grand Prix'. I know this because I recently replaced my PCM. Once you have the air box assembly out, you'll see the PCM laying flat with three connectors on top of it. Make sure those are on tight and you don't see any damage to the wires leading up to them. If the three connectors are on tight and the wires look good, you may need a new PCM. I'd say you could disconnect the connectors and look at them to make sure there isn't any dirt/debris in there but if they're on tight, there shouldn't be. But give it a try anyway and re-seat them. Just be careful not to bend any pins or damage the connectors in any way. They are a bit tough to pull out the first time. If you do all of this and still have the errors and issues, you might need a new PCM. It's easy to replace. Just disconnect the connectors, pull out the old one, put in the new one and reconnect everything. The only issue is cost. You can get one from rockauto.com but you'll then have to take it to a GM dealer or another shop that has a GM tech II scanner to have it "flashed" to match up with your specific vehicle/VIN. You may be able to find a vendor online that will flash it before they ship it, when you supply them your VIN. Either way, it's a two-cost ordeal. But in the end, it's cheaper than a new car! Bottom line, replacing the PCM yourself is easy, just costly. And just fyi, my '05 grand prix wouldn't start after I replaced the PCM. A "security feature" I learned. I had to put the old one back in, drive it to the shop, take the old back out and put the new one back in, in their parking lot (they were nice enough to let me perform my own labor) then their guy with the tech II scanner came out and flashed the PCM. So if you can find a vendor online that will flash it before they ship it, that's the way to go! Something else I learned after the fact. Maybe try partsgeek.com. Sorry for the long response. Just trying to provide as much detail as possible to help a brotha out!