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Limp Mode Issues?

Tiny
STAG1215
  • MEMBER
  • 2008 GMC SIERRA
  • 37,000 MILES
I have had my vehicle to 3 different dealers to diagnose the problem for a fix. No error codes are being stored is one issue and the service engine light is not on. Here is what happens, while drving at any speed, the truck seems to feel like it stalls. All indicator dash lights come on, (service engine, ABS, etc as well as park assist). After a brief second or so, all clears and truck resumes. I was told it is going into limp mode briefly but they cannot diagnose since there are no codes and the service engne light does not stay on. Acts like a huge hiccup. Lose everything. At high speeds, the truck will just roll through it and only the dash lights alert you it happened. Slower speeds can really be felt. I am afraid this could become a safety issue. Does anyone have any idea where to begin. I would think someone would know at the places I have been. Come back when the light stays on is what I am told. Maybe someone here can provide some input. Please
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Thursday, June 28th, 2012 AT 5:39 PM

28 Replies

Tiny
CARADIODOC
  • MECHANIC
  • 33,727 POSTS
It sounds like a dirty throttle bore this guide can help fix it.

https://www.2carpros.com/articles/throttle-actuator-service

and

https://www.2carpros.com/articles/reduced-power-limp-mode

Please run down these guides and report back.
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Thursday, June 28th, 2012 AT 6:29 PM
Tiny
STAG1215
  • MEMBER
  • 3 POSTS
Thank You.I will check. I will advise if anything changes to keep you hopping. Supposedly, they had the truck apart and checked all connections but you never know.
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Thursday, June 28th, 2012 AT 6:55 PM
Tiny
CARADIODOC
  • MECHANIC
  • 33,727 POSTS
Another thing that might help for this is to connect a scanner with "record" capabilities, or a type of flight recorder that you control. When the problem occurs, you press the "record" button, then the mechanic can play it back slowly later to see what changed. Because that data passes through the scanner's memory, the recording actually starts a few seconds before you pressed the button.

That is fairly effective with intermittent running problems on older vehicles but for electrical problems it could also affect the power source the vehicle supplies to the scanner. Losing scanner power could erase anything it memorized or recorded. On newer vehicles from the last five to eight years, there are so much electronics and computer controls interconnected, that seemingly unrelated computers can cause the problem you described. Diagnosis of those things can be easier in some cases thanks to all the computers, but when no codes are being set, finding the cause can be real frustrating, as you're finding out.
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Thursday, June 28th, 2012 AT 8:11 PM
Tiny
STAG1215
  • MEMBER
  • 3 POSTS
Thanks for the guide I cleaned the throttle body and wow the truck runs great!

Thanks
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Friday, June 29th, 2012 AT 11:22 AM
Tiny
CARADIODOC
  • MECHANIC
  • 33,727 POSTS
Nice work, we are here to help, please use 2CarPros anytime.
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Friday, June 29th, 2012 AT 7:05 PM
Tiny
CHRIS_MENDOZA
  • MEMBER
  • 1 POST
  • 2008 GMC SIERRA
It is currently raining outside and now vehicle is having engine reduced power showing. Could the rain have any effect?
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Monday, December 7th, 2020 AT 12:45 PM (Merged)
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
It might it could be a lot of things usualy turn key off and restart truck it goes away. Don't drive through any deep water with that if you did that may be the reason. Then have it scanned to see if you have any codes.
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Monday, December 7th, 2020 AT 12:45 PM (Merged)
Tiny
WRENCHTECH
  • MECHANIC
  • 20,757 POSTS
Reduced power happens when there is an issue with the "drive by wire" electronic throttle system. It usually limits you to half throttle as long as that light is on. Check for codes as hmac300 suggested and I suspect you will find some throttle codes.
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Monday, December 7th, 2020 AT 12:45 PM (Merged)
Tiny
NATRUT
  • MEMBER
  • 1 POST
  • 2006 GMC SIERRA
  • 2WD
  • AUTOMATIC
  • 130,000 MILES
I had just pulled out of the drive way and made it maybe 40 yards before a message came up saying "Reduced Engine Power". The everything was the same and running correctly except for one major thing: the accelerator would not work. I could not give any power to the engine at all. Everything else on the truck still worked as I said, the accelerator just wasn't doing anything at all. I had pulled over and cut the engine, tried again with the same results except it was like that at the start. On the third try everything was back to normal and I drove back to the house and in the driveway it sits. This all happened about 2 hours ago.
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Monday, December 7th, 2020 AT 12:46 PM (Merged)
Tiny
CARADIODOC
  • MECHANIC
  • 33,727 POSTS
You have the same "throttle-by-wire" system that put Toyota in the news a few years ago. There's no simple, reliable, lightweight throttle cable anymore that worked fine for over a hundred years. You have a computer and a multitude of sensors.

https://www.2carpros.com/articles/reduced-power-limp-mode

An electric motor turns the throttle. There's going to be a diagnostic fault code stored in the Engine Computer so it's important now to not disconnect the battery or it will be erased. That information is particularly important now with an intermittent problem.
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Monday, December 7th, 2020 AT 12:46 PM (Merged)
Tiny
JUSJOE2002
  • MEMBER
  • 1 POST
  • 2003 GMC SIERRA
  • 6.0L
  • V8
  • 2WD
  • AUTOMATIC
  • 147,000 MILES
While driving, the "reduced engine power" light comes on with no pedal reponse. Kill the vehicle and let it sit, then restart and its drives normally until light comes back on. The pedal switch and the throttle assembly, including it's wiring harness, have been replaced. I have loosened and cleaned the grounds for the battery and behind the cylinder head on the left side which connects to the firewall. Also, there is a low level buzz in the stereo speakers; and the automatic feature for the power sideview mirrors, the compass/temp display on the rearview mirror, and the keyless entry remotes work sparatically. I'm not sure what else to try.
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Monday, December 7th, 2020 AT 12:47 PM (Merged)
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Have a pro scan for codes for problems other than engine power. Check fuses under hood as well. The engine power may be the tac module that is at lh rear of engine compartment. But a pro will need to install it because modules are vin specific.
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Monday, December 7th, 2020 AT 12:47 PM (Merged)
Tiny
BINMANBILL
  • MEMBER
  • 1 POST
  • 2003 GMC SIERRA
  • V8
  • 4WD
  • AUTOMATIC
  • 190,000 MILES
While driving, everything seemed okay, the reduced engine power message came on and the truck dropped down to a max of 1700 rpm.
New spark plugs 2500 miles ago.
Any thoughts as to where to look?
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Monday, December 7th, 2020 AT 12:47 PM (Merged)
Tiny
FAST92LT1RS
  • MEMBER
  • 13 POSTS
Check/Replace the Accelerator Pedal Sensor. Check the harness for any wires pulling out of the plug. Also, there are two grounds that can come loose on the back of the block below each cylinder head. I believe they are ground G103/G104. Lastly there have been issues with wires and pins coming loose in the large connector that plugs into the throttle body. I believe the brown and yellow in particular. The part number is PT1572 or GM# 88986255. It is about $100. If that is the case you need to cut and resolder one wire at a time as all the wires are white on the replacement harness. I have heard that GM is not being very cooperative with people when addressing this issue. Hope this helps.

-Pete
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Monday, December 7th, 2020 AT 12:47 PM (Merged)
Tiny
STORMORE34
  • MEMBER
  • 1 POST
  • 2003 GMC SIERRA
  • V8
  • 4WD
  • AUTOMATIC
  • 120,000 MILES
Engine power reduce. Engine light keeps coming on
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Monday, December 7th, 2020 AT 12:48 PM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Go to Autozone its a free public service and have the computer scanned for code/s-you have a problem within the engine management system that caused the CEL to turn on-This is your starting point of diagnosis, finding out what's going on.
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Monday, December 7th, 2020 AT 12:48 PM (Merged)
Tiny
BCAT
  • MEMBER
  • 2 POSTS
  • 2003 GMC SIERRA
  • V8
  • 4WD
  • AUTOMATIC
  • 55,000 MILES
I have a reduced engine warning and truck now only idles and won't increase rpm's over 1500, no matter if accelerator pushed down or not. When I went to start it, it barely turn over, feeling like I had a near dead battery, but it did start, then service engine soon light came on, and also it says reduced engine power on message center. Any possible solutions?
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Monday, December 7th, 2020 AT 12:48 PM (Merged)
Tiny
BLACKOP555
  • MECHANIC
  • 10,371 POSTS
Get your engines computer scanned immedietely so we can find out what is wrong with it.

May be a tps issue or with the camshaft sensor due to the slow cranking.

Get back to me and I can help you find out whats wrong.
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Monday, December 7th, 2020 AT 12:48 PM (Merged)
Tiny
BCAT
  • MEMBER
  • 2 POSTS
Thanks for replying blackop555. Took truck to the shop and they found that I had a bad battery, which gave the computer grief, inturn giving false codes. Replaced battery and serpentine belt, also fuel filter. So far runs normal.
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Monday, December 7th, 2020 AT 12:48 PM (Merged)
Tiny
BLACKOP555
  • MECHANIC
  • 10,371 POSTS
Musta been a really bad battery! Glad to hear thats all it was and nothing more expensive and time consuming.
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Monday, December 7th, 2020 AT 12:48 PM (Merged)

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