2003 GMC 1500HD 6.0 "REDUCED ENGINE POWER" ONLY

[OregonASEMASTERTECH]

Here is a good one... First of all, I am ASE Master Technician out of Oregon. I personally own a 2003 GMC Heavy Half, otherwise known as a 2003 1500 HD with a 6.0 Liter and a 4L80E. It has 178,000 miles on her and she looks great and runs (most of the time, great)

 

A few months back I was driving about 65 mph, towing a trailer with a vehicle on it. I was going through a construction zone and my truck started to ever so slightly buck. Kind of like a misfire. My CEL came on and a "Reduced engine power" came on. I lost most power and it felt like I was on 3 cylinders. Now I know how a Ford owner feels most of the time. Anyways, I pulled over, turned off the key. Restarted the engine and the "reduced Power" light was out, but CEL was still on. I started to go, and had all my power back. When i got to the shop, I checked codes and found MAF codes. I checked live data and the correlation was not correct so I replaced it. That did not work.

 

At our shop, we have Identifix, and most people stated they had the following...1.) MAF issues, 2.) Ground faults at the heads and battery grounds 3.) Gas pedal Sensor 4.) TPS Sensor issues 5.) Bad alternator/draw. one or two of these usually fixes the problem.

I replaced the TPS first, Nothing.

Then the MAF as a whole, (includes new TPS on it), Nothing.

Replaced all the TPS wire harness, Nothing.

The redid all grounds, cleaned and rechecked, Nothing

Replaced pedal assy, Nothing.

Alternator is new by 6 months and tests great.

Wiggled the wiring harness while running to see if a short in the system was there. Nothing!

 

So I checked and have replaced all of the above items. I even returned them to the warehouse and got a second part to replace with just in case of a faulty part. Nothing. I checked online and people say a TAC replacement doesn't work and neither does a ECM reflash. Whats its problem? I have seen ALOT of people with this crappy issue and no one has a fix... got one??

 

My truck is now sitting next to the Fords in the lot... what a shame. I went to "just-ask" .com and they wanted me to pay a ASE Technician, not even certified Master status $32 for him to "hunt" for solutions. I have over 30+ years experience and do NOT understand why GM would make someone lose power when they need it, especially in a construction zone with no turn off's for over 2 miles and all I could do was 20 MPH!

 

Dealership has no cures, they just duplicated my above parts list.

 

If I drive down the freeway, I have to coast until 50 mph, then hit the passing gear to keep rpm's up or put on cruise control from 25 mph on up to attempt to keep the light out and the power on. It seems as if it is just under light foot when this occurs and not all the time. Last time, we did the grounds, disconnected the battery for an hour and drained the ECM. Truck worked for 2 hours in the AM, then I shut off. When I returned for another 20 mile run, it would not stop doing this! UGH!

 

My wife says she doesn't like the truck anymore and I do not blame her. She wants me to think about trading in the truck, but if GM had these issues with the fly by wire, then dodge would be my next option.

 

 

[gmtech4]

Yes, throttle body clean and was new.... brand new from a box, so "tapping" on it won't be the isuue, neither will dirt or gummy-ness. I have another ASE master tech at our place and he cannot find the fault either. We checked wiring, all good. Fuel pressure, excellent. Regulator, functioning. As stated earlier, the flow chart from this does not exist and all the grounds have been checked, double checked and triple checked, cleaned and retorqued. I do not like throwing parts at it, but it does not allow me anything to go from in reference to this problem from GM. It only happens at light throttle only.

 

I was thinking that because the spring pressur eis so low on the pedal/throttle body... that when I am driving and I apply light throttle, everytime I hit a small bump or crack in the road, it makes the pedal move. So my thought is that the TPS and the pedal TPS dotn know if I am pushing the gas or letting off, so it freaks out and sets the code.

 

As far as the LIMP mode, shit, I early got killed yesterday with a semi truck behind me. I was going 55 mph, then the reduced engine power happened. I slowed immediatly and the semi almost ran me off the road just to avoid hitting me. I understand limp mode and chryslers was good on thier 2nd gear hold to get you home. But at least you could hit the freeway and it was not life threatening.

 

If this is not fixed soon, I will sell the truck, buy a 1972 Chevy 4x4, build the nuts out of it and still have 30k in my pocket than buying a new truck.

I can't read the whole crazy thread cuzz as mentioned , no code number AND YOUR A TECH ???

 

come on , follow the code , holy crap

[OregonASEMASTERTECH]

After rechecking everything, I took it to the dealership. Tech stated a p1001 code, no communication to buss via harness behind headlight switch. He stated he found a caffed wire, rewrapped and no more issues. $327 Later, I pickedup the truck. With 7 miles, lights came back on, reduced engine power on again, cel light still has p1126. (I think that was the code)

 

I retook to dealership, they have had for 2 weeks now, must be that hidden troll under the dash?

[Jsdirt]

 

............ My point here is that poor connections are the cause of a lot of failures, are the hardest thing to locate and even harder to correct.

This is exactly why I did THIS to a '00 4.3 .

[Jsdirt]

If they do they'll give you about $500 toward a $65,000 one ....