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Denali Yukon Quits On the Highway - DANGEROUS!!


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Our Yukon XL Denali just developed an new problem. It literally quits on the road. Total lack of power, and coasts to a stop, as long and the accelerator pedal is kept depressed. The engine is essentially at an idle when this is happening. If I release the pedal completely, seems to reset itself sort of and run again, but quickly loses power again. If it had happened on a busy freeway, I'd be in the hospital or the morgue right now, cause it's almost like the brakes come on!

 

It does it driving along at more or less constant speed, but if you rapidly accelerate, it does it almost immediately and every time.

 

Did some testing and slipping it into neutral and the engine goes to idle. Tries to recover but just stumbles a couple of times. Need to let off the pedal and seems to sort of reset itself. If left in gear, the whole vehicle bucks as its slowing down, whenever it tries to start running again momentarily.

 

And the best part - can smell something burning. Coming from either under the dash or under the vehicle. Definitely not under that hood as I popped the hood to check.

 

MIL is on. Only code I can read with my Insight code reader is P0131 - low O2 sensor voltage. So, could be a bad O2 sensor, but I cant see that throwing the ECM into such a state! Should simply go into open loop mode, throw a code, light the MIL, and wait for you to get it repaired. Might also be a TQ management issue too, but no idea what would cause that to start reducing torque. Also wondering if it's the throttle position sensor on the accelerator pedal.

 

This is fricken' dangerous. My wife refuses to drive it until it's fixed, and even them we'll have to see. And, I have 3 small kids, to boot! Nice, eh?

 

Anyway, it's going to the dealer so we'll see what they come up with but is anyone has any insights or seen this, any input much appreciated.

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Yea, I get "limp mode", but my concern is the abrupt loss of motive power and the safety hazard that results. All nice for the manufacturer to protect the hardware, and it's warranty position, but at what risk to the occupants? How reasonable is this approach? Is it worth the concenquences? There is an old saying..."don't throw the baby out with the bath water". Kind of applies here, except it's more like "save the engine, kill the occupants".

 

And the worst part is, I realize that there have only been a few reported fatalities from a vehicle going into limp mode and getting hit from behind. So, you can just imagine the conversation in the boardroom, as the weigh the cost of warranty repair without limp mode to the lawsuits due to a few fatalities. Can't say I'm a big fan of that kind of logic.....

 

Not a comforting thought.

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  • 1 month later...

I was experiencing something similar in my 2015 MB C400. The collision prevention assist system would for one reason or another fail completely and during that failure the engine would go into a reduced power mode and when hitting the accelerator there would be a long pause and then a very gradual increase in speed. Happened on 3 different occasions all while on the freeway with my wife and 8 month old daughter with me. Dealership couldn't determine root cause nor was the car logging the error codes properly for diagnosis. Needless to say, I now have a 2015i Tahoe in the garage instead.

 

I agree, these limp modes are a big safety hazard to the occupants but I doubt the boardroom logic will ever change.

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If a major sensor goes offline it wont just go into open loop anymore, it triggers reduced power mode (limp home) and will drop the vehicles to a crawl to try and preserve the drivetrain.

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Take it to the dealer. GM dealers have vehicle data recorders they can put in the truck to record the event plus the GM scan tools can pull freeze frame that the ECU sets when the code was set.

 

WARRANTY. Use it.

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