LML reduced engine power, bad ecm?

[Iggy76]

Having a couple issues with my 2013 Duramax 75,000 miles

Show reduced power on the instrument panel and it feels down on power, maybe 75% of normal. But no check engine light

Also the lights dim every 5 seconds or so when at idle, the voltage goes from 14.5v down to 12.9 when this happens.

MAF reading does not change and the only change when I unplug it while running is the idle increases, no check engine light.

Boost goes up to about 17psi

I have a tech2 and it will not connect to engine data or a few other data pids.
It did when I first tried it but now it just says Possible Wrong Vehicle Selected

Im thinking it might be a bad ECM but want to confirm if possible before I order one.

Truck is deleted and has a Ridgerunner 5 position tune.


I bought it from an auction after it was in an accident, drivers fender, hood and bumper were damaged. After fixing the damage I drove it for about 3000 miles without issue until Reduced Engine Power came up on the dash.

Rubbed through wiring is also a concern and plan to look into this more.

 

[Chevy1925]

More likely the tcm than the ecm

 

[Iggy76]

More likely the tcm than the ecm

Really? Anything I can check to confirm?

 

[Dallas S]

09-15 TCM are common to fail. But I haven’t had one set the reduced engine power message or effect MAF readings.

I’m going to ASSUME a few things here, but maybe try telling the tech 2 that the truck is a 2011, not a not a 2013

 

[KyleC4]

Well sounds like possibly a few things could be going on here. And with truck being deleted I’m assuming no check engine light due to tune....? Biggest thing I look for here with reduced engine power is air leak equivalency ratio (aler)reading with your tech2. With everything as it should be I believe it should read between .9-1.1 but yes definitely go through wiring and grounds for possible issues.

 

[Iggy76]

09-15 TCM are common to fail. But I haven’t had one set the reduced engine power message or effect MAF readings.

I’m going to ASSUME a few things here, but maybe try telling the tech 2 that the truck is a 2011, not a not a 2013

I'm not leaning towards the TCM either but am keeping an open mind.


Putting it as a 2011 worked, I can access all data now on the Tech 2


The MAF reading is 625.02 G/S and 65535 HZ and it does not change. Again no check engine light when I disconnect it but I do get a check engine light when I unplug the MAP sensor so I know the light works.

Reduced engine power Hi speed limiter is Active


The ECM was pushed over from the accident and the wire cover on the front plug was broken but the wires and everything else seem ok. I will get a picture of that. I can do a continuity check on the MAF wires if needed but I don't have access to a wiring diagram to see what plug they go to in the ECM.

 

[Iggy76]

Well sounds like possibly a few things could be going on here. And with truck being deleted I’m assuming no check engine light due to tune....? Biggest thing I look for here with reduced engine power is air leak equivalency ratio (aler)reading with your tech2. With everything as it should be I believe it should read between .9-1.1 but yes definitely go through wiring and grounds for possible issues.

I did not come across that while looking over the data on the Tech 2 but can with a little guidance.



I do appreciate any help and effort, thanks.

 

[02greysixer]

If MAF is that high with the engine idling or off that is your issue. You just have to figure out whether it be th MAF itself, wiring or ecm. Most lml's I've seen hang around 30-35 g/sec at idle
I had an lb7 do something similar years ago and found a bug lodged in the MAF. New sensor and all was well.

Sent from my SM-G960U using Tapatalk

 

[juddski88]

If MAF is that high with the engine idling or off that is your issue. You just have to figure out whether it be th MAF itself, wiring or ecm. Most lml's I've seen hang around 30-35 g/sec at idle
I had an lb7 do something similar years ago and found a bug lodged in the MAF. New sensor and all was well.

Sent from my SM-G960U using Tapatalk

I don't think that's causing the swings in voltage, even if there was a shorted circuit in the sensor. Sounds like a bad ground or a rubbed through harness or something. But certainly won't rule out a bad module yet either.

 

[Iggy76]

If MAF is that high with the engine idling or off that is your issue. You just have to figure out whether it be th MAF itself, wiring or ecm. Most lml's I've seen hang around 30-35 g/sec at idle
I had an lb7 do something similar years ago and found a bug lodged in the MAF. New sensor and all was well.

Sent from my SM-G960U using Tapatalk

I wouldnt think its just the MAF as it doesnt change when unplugged.

Wiring or ECM is what Im thinking and Im about out of things I can do at home so it will go to the shop for further diagnosis and repairs.

 

[Iggy76]

I don't think that's causing the swings in voltage, even if there was a shorted circuit in the sensor. Sounds like a bad ground or a rubbed through harness or something. But certainly won't rule out a bad module yet either.

Computer from what I have read turns Alternators on but does not control the voltage, that is from voltage reg in the alternators which could be that issue.

My truck has dual alternators, Im going to try unhooking one at a time to see if there is a change.

 

[Blackmax123]

Definitely make sure the alternators are grounded. I chased a charging system problem for a while on my old lml and found the alternator wasn't getting a good ground through the accessory bracket to the head.

 

[Iggy76]

Definitely make sure the alternators are grounded. I chased a charging system problem for a while on my old lml and found the alternator wasn't getting a good ground through the accessory bracket to the head.

Did that yesterday with a set of jumper cables.

My truck has dual alternators so I'm going to try unhooking one at a time to see if that has any effect.

 

[Iggy76]

I don't think that's causing the swings in voltage, even if there was a shorted circuit in the sensor. Sounds like a bad ground or a rubbed through harness or something. But certainly won't rule out a bad module yet either.

I agree.

 

[Iggy76]

Today I unplugged each alternator at a time and doing so stopped the voltage drop. Not sure what that means yet.


Also ordered a new MAF to try before it goes to the shop, should have that tomorrow.

 

[juddski88]

Today I unplugged each alternator at a time and doing so stopped the voltage drop. Not sure what that means yet.


Also ordered a new MAF to try before it goes to the shop, should have that tomorrow.

So you mean that unplugging each one has the same exact effect? Or just unplugging the first one you tried had that effect?

 

[Iggy76]

So you mean that unplugging each one has the same exact effect? Or just unplugging the first one you tried had that effect?

Same effect when unplugging either one.

 

[Iggy76]

Got the new MAF today and I'm confused, are the 2 sensors on the airbox both MAFs? The one on top I thought was the MAF til it showed up and that one is not on GMs website. The one on the side is what showed up and online they are both called a MAF sensor. So after figuring out the other part i ordered it because one of the little sensor wires was broken. The new side sensor made no difference but both sensors were dirty and salty so I don't mind replacing them. The previous owner obviously did not take the best care of this truck.

 

[02greysixer]

I believe the other one is a humidity sensor if I recall correctly. If the filament was broken in MAF sensor replacing that should take care of your power issue.

Sent from my SM-G960U using Tapatalk

 

[Iggy76]

I believe the other one is a humidity sensor if I recall correctly. If the filament was broken in MAF sensor replacing that should take care of your power issue.

Sent from my SM-G960U using Tapatalk

No change with the new MAF sensor, humidity sensor is ordered and is also called a MAF, I cant find a sensor called a humidity sensor