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2003 GMC 1500HD 6.0 "REDUCED ENGINE POWER" ONLY
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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.
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