LMM Engien power reduced

[vettemakesemwet]

Working on a previously deleted and tuned(NOT BY ME) LMM 2009 Silverado. Customer states vehicle goes into "engine power reduced", and I have confirmed as such. There are no codes, no CEL, no nothing except the engine power reduced in the cluster. In the scan tool under fuel system data, reduced engine power is set to active. There is no data PID I can find that tells me why, and with no codes I am at a loss.

Since I do not normally tune diesels, this next statement may be incorrect in some ways, but there are codes disabled that I think should never be disabled no matter the tune or delete. It looks like the person decided they didn't want to diag or fix any issues, just delete the code and sweep it under the rug, so to speak.


Here's the question. Have any of you ever seen a Duramax go into engine power reduced without ever setting a code?

I think I may need to edit the tune, turn a bunch of codes back on so I can diagnose the issue and repair the truck.


Am I on the right path here, or does anyone have any other ideas?

Thanks!

Edit to add, please excuse my misspelling, I was typing in a hurry, and can't edit the title. My poor typing will forever be immortalized on the internets.

[gtstorey]

On some GM stuff the test will still run on a disabled code and can trigger a reduced power, but the DTC that causes it will not set. Does the reduced power clear when you cycle the key?

[vettemakesemwet]

Sometimes, but it comes back on 95%+ ignition cycles at some point. For a quick reference, all 8 injector flow rate incorrect codes, IMMO codes, PCM internal memory codes, fuel pressure too low and too high(P0087/88) and many others are all disabled. I have a decent amount of GM gas tuning experience, and have heard of the gassers doing the same thing of running tests even if code is disabled. Just never seen any Duramax go reduced power without some sort of code setting too until now, hence why I think I need to re-enable some and see what happens.

[Pumpkin]

I have an 08 with the same problem. In my case i found the reduced power would set after 5 minutes, regardless of just idling, or driving. I did a particulate filter regeneration, even though its not there, and the problem seems fixed . I only have 100 miles on it, and so far, so good.

[Lennydmaxguy]

I have an 08 with the same problem. In my case i found the reduced power would set after 5 minutes, regardless of just idling, or driving. I did a particulate filter regeneration, even though its not there, and the problem seems fixed . I only have 100 miles on it, and so far, so good.

The problem will be back at some point. Until the ECM is told that it no longer has a DPF, it will always act as if it has one.

[vettemakesemwet]

Just for closure and the fact a lot of people never report back what was found, I figure I would. So here's what I found out. The truck had been deleted for some time. Someone suspected the BCM had failed, so it was replaced with a used one, but truck still had issues, I don't know what, this is what I was told by the customer. Then the ECM was replaced. The truck was taken to someone who used HP tuners to try and do the delete. In the process, he/she/it removed all sorts of codes that should NEVER be removed, as I stated above. That person could not fix it, so it came to me. I restored all the codes that should not have been removed, and none set. I was able to do enough cold starts on it to find it would go into reduced power mode once warmed up a bit. It would do that consistently, as well as when already warmed up would go to reduced power fairly quick after restart. At one point, the dash flashed a message of "exhaust filter full, service now", or something of the like.
End result is the vehicle was deleted with an incapable tuner, by someone who did not know what they were doing. I refuse to do deletes as it is not worth it to me, nor will my tuner do them anyway. Informed the owner there was nothing I could do, and they would have to find a shop to do it right, but I was unable and unwilling to go any further.

Pretty sure Lenny has it right, the ECM still thinks there is a DPF there, even if the other codes are disabled. Repeated "regens" are in your future Pumpkin. Best of luck guys!