2003 GMC Envoy Powerloss

[RKenn]

Hello:

With no warning or indication, the engine loses power and the service engine light appears. I can still drive the car, but it has no acceleration.

This problem has occurred twice in past 8 months. #1 when accelerating thru an intersection after being stopped. #2 when driving 65 mph on interstate and trying to accelerate.

Both times the computer pointed at the clutch fan or associated parts. But the dealer wont try to fix it since they cant replicate the problem after rebooting the computer (HS!).

I am left with a dilemma. This is a dangerous situation. I have to drive the car, but I have no confidence in it. I still have 5 payments to make before I think of selling (and I had planned to hold onto it for 3 more years). Does anyone have a suggestion to make GMC do the right thing and replace the suspect parts?

Regardless, the fact that GM placed a "kill switch" in my car means I will NEVER purchase one of their corrupt products again. GM deserves to be bankrupt and out of business.

Thanks for your time.

[maxwedge]

Welcome to AF, not GM's issue here, but a dealer that is gun shy to attempt a repair, we need the code and more symptoms, the fan clutch can be an issue here, very common, or a sensor issue that engages the clutch on high and reduces power to save the engine. Replace what parts, there is, as you say, no definitive diagnosis I would address this with the service mgr at the dealership if there is no forseeable resolution.

[BRD]

FWIW, my wife's '03 did that in the spring of '04 or '05. Took it to the GMC dealer, they did an updated re-prog of the PCM. It's been OK since. Unfortunately, the scan won't tell you what caused the PCM to lose its instructions. I've wondered at times whether it could have been a freak radio or microwave signal, or possibly something as low tech as a magnetized tool being passed near it, like during an oil change. On the Chevy Trailblazer board there's a new post by an owner of an '02 (same powertrain) to the effect that his PCM was defective and had to be replaced. I'd need to check the owner's manual, but there's a good chance a factory-defective PCM would be covered by the 8-year emissions warranty. At the very least, if you went back to the dealer that originally sold you the vehicle and their shop diagnosed a bad PCM, I think they'd work with you to try to get GM Customer Service to take care of the cost to replace & re-prog. GM doesn't want their products going dead in traffic, very dangerous.

[RKenn]

Thanks for the responses. Tis a perplexing and frustrating issue.

Sounds as if I need to go back to the dealer and have them run a full diagnostic. Of course, they say they have already done that.

Anyway, thanks for your time...

[RKenn]

Forgot to add: The Service Code # is: 1271; they say "3 bulletins for the code. May be fan clutch App. or wireing code. DIA time only"

Thanks

[BRD]

That particular DTC indicates your accelerator pedal position sensors 1 and 2 aren't in sync. If one of sensors goes bad, it's possible the computer sends a kill message to the fuel pump. I dunno, but I don't know, either, what vehicle you can even get any more that still has a mechanically-linked accelerator pedal. If I had my way we'd still be driving carbureted power plants with standard transmissions.

[envoyxuv]

This document number, 1561633, refers to a condition where the cooling fan 5 volt reference signal can intermittently short to battery voltage (12+ volts). This 5 volt reference circuit is shared by multiple components, including the accelerator pedal. The bulletin directs the technician to perform a test to verify whether the fan is in fact internally shorting to battery voltage or not. The loss of power you experience is the powertrain control module defaulting the motor controlled throttle to idle and ignoring the input from the accelerator pedal. This is a safety feature to prevent the vehicle from accelerating out of control if something goes wrong with the accelerator pedal sensor. It does make a person wonder what was ever wrong with a throttle cable.

[BRD]

Great follow-up info. It's just anecdotal re my wife's '03, AFAIK, but last Spring the OEM fan clutch did fail in service (wouldn't let go) and GM Customer Svc covered the whole tab with the dealer to replace with the updated (post-05) fan clutch and re-flash per associated TSB. Shop diagnosis on the bad fan clutch said "shorted." So maybe that was the problem all along - i.e., the earlier PCM fade-out.

[RKenn]

Thanks everyone for your responses. As a followup, this condition continues to occur with more frequency. But remains random. I inadvertently discovered that once I kill the engine and restart it, the power returns and the engine works fine. So, I am forced to pull off the road and then restart the engine prior to getting to my destination.

At some point, it will happen when I am close to the dealer and I will take it in without cutting the engine. Irks me that the dealer did not tell me this and that I had to discover this on my own. Would have alleviated some stress. But, I am still left with a car I can not depend upon.

[BRD]

Good luck and let us know what the malfunction turned out to be. Like I said, I had not previously associated the PCM crap out on my wife's with the seized-up fan clutch replacement, if for no other reason they occurred (I think) 3 years apart. But you and others in this thread may be on to something that's a common cause of gray hair among Trailvoy owners and takes more time to materialize than some techs are willing or able to spend with a scanner trying to figure it out. Some automotive problems are still like that, even in the electronic age. The tech who can attack the read-out with knowledge of the product, wrench experience, and horse sense is the one you want - same as a doctor or dentist.

[RKenn]

Hello everyone:

Sorry for the delayed response, but my car's problem was finally determined: the acelerator sensor had gone bad. Of course, I had to endure a number of trips to the dealer before they came to this conclusion.

It was fixed a few months ago and I have not had any problems since.

Thanks for everyone's responses. Was maddening at the time...and I remain determined to not buy another GM car. Of course, with the way things are going we may not have that option in a few years anyway.

Just letting ya know...

Thx,
RKenn

[jdmccright]

Sorry to hear such discouraging words. I've been a GM owner of one truck or another for over a decade. I can understand your frustration, but bear in mind that a bad accelerator sensor is really a fluke problem. Dealerships who have the repair experience will know what the more common causes of symptoms are and look at those first...I certainly wouldn't have guessed the accel sensor at first, especially with a fan clutch fault code .

Anyways, I'm glad you found and posted the problem for all to see and hope your Envoy will be trouble-free from now on. Take care!