[gojeda69]

Vehicle:
2003 Envoy XL SLE
4.2L I-6
Mileage: 92,000

Hi everyone -

I am desperately looking for help on the rather serious REP issue.

Yesterday, for example, REP manifested itself no fewer than 45 times while my girlfriend was driving it. Today, I took the vehicle for my usual 34 mile commute and I got it once.

Symptoms: In the 10-20 seconds leading up to the truck going into REP mode, throttle response is sluggish and or "notchy" (meaning the truck accelerates not smoothly or linearly, but in a 'stepped' mode). Then, there is a moderate shudder lasting, at most, 2 seconds, then - boom into REP mode. Both Check Engine and REP lights come one.

Turning the truck off/on gets it out of REP mode. Check engine light stays on.

Environment: South Florida winter, little rain, low moisture. I was thinking we were looking at some sort of moisture issue with the wiring or harness, but in this rather dry enviroment I am not seeing it. Also, during rainshowers - the REP neither increases or descreases.

I've been dealing with this issue for a year now, if not more.

What Has Been Done:
I have replaced the Throttle Body Assembly (Delco). This did not alleviate the TEP issue.
I took the truck to the GMC dealer. They have no idea what was going on but noticed that fuse-box was out of a Trailblazer and not an Envoy. They said this could be a cause, but not 100% certain. That repair\labor cost me $1200 and did not resolve anything.

What I do have, but have not installed yet, is an accelerator, throttle-by-wire assembly. I got that after reading in some spots that this could be a culprit.

Codes:
After having the check engine light on for a while, I hook up the code reader to it and it comes back with these codes:

P0171
P0172
P0340
P1221
P1516
P1481

I cleared the check engine light and codes then took her out for a ride to try to induce another REP. Upon starting the motor, I get the following code:

P0340

HOWEVER, this code does not trigger the Check Engine or REP light.

About 15 minutes into my ride, the usual shudder and REP event occurs. This time the reader tells me:

Code 1: 1221
Code 2: 0340
Code 3: 1221

Odd that 1221 showed up twice.

Anyway, engine-codes.com tells me that GMC 1221 has to do with TPS 1-2 correlation. As mentioned before, this is a genuine Delco aftermarket throttle body\TAC.

I still have the old throttle body.

I will also note that the engine idles rather roughly. I thought it was an engine mount issue, but a mechanic friend of mine took a quick look at it and said it was OK there.

So, I am wits end here. I cannot discern a pattern and I need this vehicle to be working properly.

Any ideas would be *greatly* appreciated.

George

 

[EnvoyBoy2004]

With some of the codes you are posting, and the intermittent nature of the symptoms, it would appear that the problem may be with the fan clutch harness. In the harness is a 5V reference signal that is also used by the TPS and Accelerator Pedal assembly. There have been reports of chafing of the harness in the area of the radiator supports. Try following the harness from the fan clutch connector.

 

[gojeda69]

With some of the codes you are posting, and the intermittent nature of the symptoms, it would appear that the problem may be with the fan clutch harness. In the harness is a 5V reference signal that is also used by the TPS and Accelerator Pedal assembly. There have been reports of chafing of the harness in the area of the radiator supports. Try following the harness from the fan clutch connector.

Im familiar with the harness\connector for the fan-clutch that sits on the upper part of the radiator, driver side, right next to the fan. Is this the harness you speak of?

If it is, I have checked it and will check it again. The last time I checked it, I wiggled it - vigorously - trying to induce something, but nothing happened.

I will check it though again and report back. Thank you for the response.

 

[gojeda69]

I have some additional notes to add.

Today, two things occurred.

1. When starting the vehicle cold, the vehicle holds on to 1st gear too long under moderate acceleration. When it does grab 2nd, it does so rather roughly. This goes away once the vehicle is up to operating temperature.

2. After my 35 mile commute, upon hitting the light at the end of the exit ramp I take, the vehicle shuddered violently, engine almost went off, and message center said "OIL PRESSURE LOW" then "STOP ENGINE" for a few seconds each. NO REP light appeared. Check engine light was already on. Engine stabilized itself a few seconds after that, but at a highly elevated IDLE speed (almost 1000 RPM).

I have seen this before where the vehicle sit at this high idle. Sometimes restarting the vehicle helps being the idle back down, sometimes it does not.

Also - not sure if I've mentioned this in the OP, but the truck does idle roughly all the time. The idle is relatively stable (until the motor starts hiccuping just before the dreaded REP appear) , but it is rough - and, of course, more pronounced when the vehicle is cold.

Lastly, I should note - the engine has no trouble starting at all.

 

[Lebakken]

gojeda69,

Any luck with a permanent fix on this issue yet?

My '06 Envoy XL(Straight 6 cylinder with 155k miles) just had a similar event this morning. Wife was driving it, REP and Check Engine light came on at a stop light, and she attempted to move forward when it got sluggish and low idle/ruff idle. A restart allowed her to get moving again, and then at her destination a shut down and restart got both lights to go out.

Is this a wiring related issue?

Thanks,

Jerry

 

[gojeda69]

Unfortunately, no - no luck in finding a solution. I haven't had much time lately. Not sure how much time I will have, to be honest. I plan on getting rid of the truck the first opportunity I have because of this issue and also I need something bigger to tow the boat with.

I will get around to replacing the accelerator assembly, which probably is not the culprit, but I have it here and it has been bought.

If I come across anything Illl post it here.

 

[Lebakken]

Thanks for the update gojeda69.

Not to hijack your thread, but the SES light came on tonight. And so I took it over to AutoZone to check the codes with the light on. No REP today though.

Symptoms -
REP and SES light illuminated at a stop light, and then vehicle stalled in the middle of the intersection.
Restart of the vehicle and resumed driving, normal speeds, REP and SES still light up.
Restart at destination, cleared both lights. idle appears to be a little "rough"
Cold temperatures last few days.. Today, subzero start (-8 F with -29 wind chill)

Today, SES light came on at stop light, rough idle but cleared when moving.

Codes that popped up;

P2101- Throttle position (TP) sensor does not agree the APP. The ECM has detected the TPS angle does not agree with the APP commanded angle.

Probable cause -
- Check for binding throttle plate
- Poor circuit connection - Check TAC module connector for water
- Failed APP or TPS


P1515 - TAC module throttle actuator position performance. The ECM has detected an out of range condition between the predicted and actual throttle position.

Probably cause -
- Poor connection at the TAC module
- Failed TAC module
- Check TPP or TPS sensors
- Binding or bent throttle plate-failed throttle body

In speaking with guy who ran the codes, he was leaning towards the throttle body failing and needing replacement.

The SES light went out before driving home. Slightly rough idle when stopped.

By the looks of it, I am in for a throttle body change out.

Thoughts?

Thanks,

Jerry

 

[gojeda69]

Hi again,

I have not forgotten about this thread, just no developements on my end.

Lebakken - all the things you've mentioned in your post I have seen on my Envoy:

- SES
- REP
- Engine Starts Up, but ROUGH IDLE

I believe I have gotten the two codes you've mentioned as well.

Question: You said, "Restart of the vehicle and resumed driving, normal speeds, REP and SES still light up."

Are you saying there has been times REP lights up, but the vehicle perfoms normally? That has never happened to me. REP always means reduced engine performance for me.

Anyway, that being said, I have replaced the throttle body - genuine GM parts - and I still kept (and keep on getting) SES\REP.

Do I think it is worth replacing? Yes - unfortunately, this is one of those issues where you are going to through a litany of things to get it fixed.

If GM doesn't know how to fix it, then you can imagine what we are up against.

This is turning out to be a huge mystery.

I still need to install the new accelerator pedal assembly - maybe this weekend.

One other thing I have noticed recently. When REP appears, and I manage to get rid of it, the fuel gauge registers a line or so LESS fuel. It eventually, slowly, goes back to the normal level.

This could be a product of the crappy step motors GM used for these dashes on our trucks.

Anyway, Ill report back when something new arises.

PS: Forgot to add. Did a MPG fuel run recently with my truck. Got 19 MPG for the tankful.

 

[Lebakken]

Hi again,

I have not forgotten about this thread, just no developements on my end.

Lebakken - all the things you've mentioned in your post I have seen on my Envoy:

- SES
- REP
- Engine Starts Up, but ROUGH IDLE

I believe I have gotten the two codes you've mentioned as well.

Question: You said, "Restart of the vehicle and resumed driving, normal speeds, REP and SES still light up."

Are you saying there has been times REP lights up, but the vehicle perfoms normally? That has never happened to me. REP always means reduced engine performance for me.

Anyway, that being said, I have replaced the throttle body - genuine GM parts - and I still kept (and keep on getting) SES\REP.

Do I think it is worth replacing? Yes - unfortunately, this is one of those issues where you are going to through a litany of things to get it fixed.

If GM doesn't know how to fix it, then you can imagine what we are up against.

This is turning out to be a huge mystery.

I still need to install the new accelerator pedal assembly - maybe this weekend.

One other thing I have noticed recently. When REP appears, and I manage to get rid of it, the fuel gauge registers a line or so LESS fuel. It eventually, slowly, goes back to the normal level.

This could be a product of the crappy step motors GM used for these dashes on our trucks.

Anyway, Ill report back when something new arises.

PS: Forgot to add. Did a MPG fuel run recently with my truck. Got 19 MPG for the tankful.

After a restart of the vehicle, was able to drive "normal" and at final destination, and another restart, the REP & SES light went out.

The REP light has not come back on since that day, and the SES light has not either. I pulled the air filter and replaced it, it was a little dirty, but shouldn't have caused the REP to light up.

My first decision will be to pull the Throttle body out a give it a cleaning. vehicle has been driving ok, idles does feel a little rough. but not excessive.

The temperature here hasn't been ideal for pulling the TB out. Might be warm enough this weekend to try for it.

I will let you know how it runs after this weekend.

 

[gojeda69]

Hi - Im back.

So, I went ahead and switched out the accelerator assembly, which you may or may not know is throttle-by-wire on this truck. It was a royal pain in the ass to switch out, but I got it done.

Of course, I disconnected the battery before starting.

So, after switching the unit out, I started her up. I noticed a couple of things.

1. The truck still idles rough, however the hesitation that I was feeling when pressing on the accelerator from a standing start is, for the most part, gone. She does not accelerate any quicker or anything like that.

2. As mentioned, the idle roughness is unchanged. The roughness is significant enough that it rattles the grill a bit - and that be heard from inside the truck. Idle seems to be ok at 700 RPM or so.

3. The "whoooooooooa" sound of the fan clutch seems to be a bit more pronounced and seems to linger a bit until 40 MPH. Before I switched out the accelerator, the fan clutch sound stopped when the tranny shifted from first to second.

4. I took her out for a 30 minute spin. About 10 minutes into it, to my disappointment the REP manifested itself. I did the usual: pulled over to the side of the road, turned the car off, waited 10 seconds, then turned her back on. Check Engine light stayed lit, but REP went away - and I was able to drive the truck normally.

5. About 10 minutes later, I stopped off at CVS to get something. When I came back out, the Check Engine light was gone - which is unusual because it usually lingers for about 4-5 times the ignition is turned on to start - and only then if no new codes appear, it will go away. But like I said, the next time I started the truck, the SES was off.

There was no other drama for the rest of the trip.

What I do notice is still some irregular throttle response at around 20 to 30 MPH. The truck bogs down, not accelerating as you would expect her to.

...and of course, the rough idle.

She will do her usual 70 mile round trip commute today, so we will see what is in store for me then.

Ill keep you guys posted.

 

[gojeda69]

Quick update....

So after replacing the gas pedal assembly and going through my regular commute, I have to report that the issue has not been resolved.

I am still getting the usual SES/REP condition with no rhyme or reason.

I am about to set this vehicle on fire and drive it straight into a canal. VERY frustrating.

So I am not even sure where to go from here. I am thinking about sending off a letter or a phone call to GM regional - or even Detroit - to see if I get any sort of traction. In the meantime, I am going to look into getting rid of the Envoy.

$1500 in repairs and parts and I am no closer to resolving the issue.