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Reduced Engine Power Message

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#16 BigSilver



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Posted 09 July 2008 - 10:16 PM

I figured I'd add my hypothesis for the record to this old, but relavent thread ...

Recently my 2003 Chevy Burb experienced the "reduced engine power" syndrome. At the time I was operating the A/C and driving along at about 15mph in city traffic for about thirty minutes. Pulled over to pick-up a passenger, then idled for about a minute.

Put it into gear, and suddenly bing, bing, bing "reduced engine power". Temperature guage displayed regular operating temp of about 200F, and regular battery charging voltage of about 14Vdc.

So I pulled over and tried to rev the engine. Nothing more then about 750rpm and a bit rough. Turned the engine off, waited a minute then restarted. Same reduced power scenario. Turned off the engine again and popped open the hood this time. Looked around for coolant leaks, or any signs of abnormality. Nothing visible. Did detect excess radient heat upon opening the hood, though. So I left it open for about a minute, until my patience ran out. Closed the hood and started the engine again, making sure my A/C was off. Perfect start, 100% power as if there were never a hickup.

This has happened twice so far, only in city traffic and both times with the A/C on. Haven't checked for error codes as yet, but suspect insufficient engine bay cooling coupled with A/C demand, causes the engine to reduce power to protect itself.
I do recall the sound of the cooling fan becoming louder and pronounced prior to having the "reduced engine power" glitch.

Have used the A/C while driving on the highway, for over an hour duration and no reduced engine power scenarios; ergo adequate cooling.

#17 kal el

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Posted 09 July 2008 - 11:24 PM

do a search for reduced engine power, I had the same problem on mine and there is a lengthy(sp) procedure to diagnose this. mine actually had a small hole in the tps and was letting moisture build up and throw off the electronics inside. the gas pedal has a sensor and the tps has a sensor and they have to be reading the same or you will go into reduced power mode. I went thru the whole thing and couldnt find the problem dealers didnt want to put a new tps on so I finally did it myself and havent had a problem with it since.

#18 Texas Jim

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Posted 10 July 2008 - 07:01 AM

I am assuming that it is DRIVE BY WIRE.
If so, it would HAVE to have two TPS sensors to have any kind of safety margin.

They have to agree of the computer, (figurativly) just throws up it's hands and says...
"I don't know what you want to do... so I am not doing ANYTHING." and shuts off most of the fuel.

If it only had ONE TPS... and if malfunctioned... it could command wide open throttle (or anything in between) AT ANY TIME. That would usually be considered... NOT GOOD. :ughdance:

There has to be feedback and agreement between the two, for it to operate properly.
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#19 D&SYukonDenali


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Posted 10 July 2008 - 07:11 AM

My guess, sometimes sensors go bad (happens when they are made in China). Had the samething happen on a BMW Z3 with only 5000 miles.

Do you have other electrical problems happening (dimming headlights, flashes in some dummy light on the dash, ect)? Is so, could be a bad ground somewhere in the electrical system (my brothers Chevy pickup had this problem).

#20 M. Cueva

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Posted 10 July 2008 - 08:53 AM

This is most likely the culprit:

Posted Image Service Information
2003 Chevrolet Chevy C Silverado - 2WD | Sierra, Silverado (VIN C/K) Service Manual | Document ID: 1869994 #PIP3089B: SES Light And Reduced Engine Power DTC P0120 P0220 P1516 P2135 - keywords accelerator actuator APP blade body connector connection DTC L33 L59 LH6 LR4 LM7 LS1 LS2 LQ4 LQ9 module position reduce sensor - (Oct 31, 2006)

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Subject:SES Light and Reduced Engine Power DTC P0120 P0220 P1516 P2135

Models:2004-2006 Buick Rainer

2005-2006 Cadillac CTS-V

2003-2006 Cadillac Escalade

2003-2006 Chevrolet Avalanche, Corvette, Express, Monte Carlo, Silverado, SSR, Suburban, Tahoe, Trailblazer

2003-2006 GMC Envoy, Savana, Sierra, Yukon

2003-2006 Hummer H2

2005-2006 Pontiac GTO

Equipped with a 4.8 5.3 6.0 or 7.0 V-8 Engine

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

A vehicle may be brought into the dealer for a reduced power message, and DTCs P0120, P0220, P1516, P2101, or P2135.

The Throttle Actuator Control (TAC) / throttle body type trouble codes, may be caused by a loose wiring crimp at the throttle body connector, or a broken throttle body circuit.

Complete the current SI diagnostics for any symptoms or trouble codes found. If a intermittent T/P or TAC module type code is occurring complete the inspections below.

  • Inspect all related throttle body terminals for a loose wiring crimp. The loose crimp may be difficult to find, and the poor connection will be between the terminal and the copper strands of the wire. Wiggle test the individual throttle body circuits to see if the concern can be duplicated.
  • Inspect the related circuits for broken wires inside the insulation. The outer wire insulation may look fine, but the internal copper strands may be partially broken. Breaks in the wires usually occur within 1 to 4 inches of the throttle body connector. Wiggle testing may also induce a trouble code to set.
  • On C/K trucks complete SI procedures for voltage drop on grounds G103 and G104. Grounds G103 or G104 may be loose or corroded.
If a terminal crimp or a broken wire has been found, repair or replace only the circuits involved. There is a throttle body pigtail connector available through GMSPO, but installing this pigtail connector may cause other intermittent TAC module/TP codes at a later date. If this pigtail must be used, please follow the SI procedures for Splicing Copper Wire Using Splice Sleeves. (the proper Kent-Moore crimping tool must be used for this repair)

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.


2008 General Motors Corporation. All rights reserved.
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#21 Raptor f22

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Posted 06 February 2009 - 07:47 PM

I have an 03 Sierra with the exact same problem, and the dealer cannot duplicate the concern. However, when you lose all throttle control on the freeway, it is not a "good thing" !
They wanted to throw a new throttle body at it, as the TPS is not available as a seperate part. I showed them the post about the wiring, but they said the wiggled the wires, and could not duplicate the code/problem.
They also said, I may need a new TAC module.
I am convinced they are just throwing parts at the problem.
Any advice?? Anyone else had this problem??

#22 kal el

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Posted 06 February 2009 - 10:06 PM

like I stated awhile ago I went through the tsb and had no bad or loose wires. I replaced the tps and found a small crack in the back that was allowing condensation get in and throwing off the signal or voltage to the sensor on the gas pedal, the didint agree so goes to limp mode. I bought the new tps from the dealer was about $160 and took about 10 minutes to put on. 3 dealers told me that you needed a tech 2 to sync it but it does not need to be synced. this might not be the problem but 3 dealers couldnt duplicate and none wanted to put the part on without it doing it, so I just did it myself and glad I did.

#23 Raptor f22

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Posted 07 February 2009 - 01:28 AM

Isie, what year truck, and what engine do you have?
I was told the TPS is not sold/replaceable seperately from the throttle body, and that it costs more than $160.

#24 kal el

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Posted 07 February 2009 - 08:25 AM

I have an 03 2500 hd but it is the exact same as on the 5.3s I also have an 03 1500 z71 with the 5.3. you are right the sensor is part of the throttle body , I know that is all I paid for it from the dealer. email me and i will send pics of the one I removed I do not know how to post pics in here.Also I dont know if it is available yet from aftermarket.

#25 wheelsthatgrip



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Posted 07 February 2009 - 08:54 AM

It means you may have bought a Ford :angel:

#26 Raptor f22

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Posted 07 February 2009 - 02:43 PM

Thanx for the update, that does look like my throttle body.
I just hate throwing parts at a problem without being sure, but intermittent electrical prbs are the hardest to find.

I dont understand the "you may have bought a ford" comment.... I have owned enough fords to know they also have unique problems of their own.

#27 the blur

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Posted 13 December 2009 - 06:54 PM

I replaced my throttle body 2 times.
The 1st one was defective. CARDONE s^cks a$$.

all my throttle body codes are gone.
$150 for the TB.

100,000 miles I'll throw some parts at it, no problem.
better than paying $100 per hour trouble shooting an intermittent problem, which they won't find.

and the dealer will never be able to duplicate the problem, TB problems are so intermittent.
mine would throw a reduced engone power every 6 months, and this went on for years, until it was once a week, and then once a day. until I wouldn't let the wife drive it any more.

Edited by the blur, 13 December 2009 - 06:55 PM.

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#28 berger1980



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Posted 01 April 2015 - 03:43 PM

I know it's an old topic, but my 2005 Sierra SLT has had this issue in the past. Last week I replaced my alternator, and started having REP right after. It happened twice intermittently, and I was not doing the same thing when it happened. I browsed through a bunch of threads after it happened again. I found one from an old GM tech that said to check the harness behind the throttle body. DO TELL-I found 1 of the wires (yellow specifically) had cracked insulation about 1" behind the purple insert that separates all the wires. I gently pulled on it and it snapped. I looked closely with a magnifying glass and there was literally 1 strand of the copper left intact that I had broken off. The crack in the insulation had let enough moisture and road corrosion in that it had corroded most of the copper. 

I stripped the wire back on each end and applied a butt-connector until I got to the dealership (I only went there because a good friend owns it). His tech removed the old plug and cut the wires. Used new terminal connectors and soldered them on for a guaranteed connection. Replaced, test drove, and no more issue.

He also sent me a service bulletin they had, #PIP3089B that was directly related to the codes thrown by the TB.

The way I found it was from a good start (when NOT in REP) open the hood, remove the engine cover, and gently wiggle the harness behind the TB. I was able to induce REP by wiggling the harness-thus pointing me in the right direction. I took so much time reading and asking questions, I hope someone, even one person can use this info. I read where people have dumped thousands of dollars in repairs, just to have it not work. Mine cost me $94, WITH an oil change.


Good luck-

#29 Veronica



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Posted 21 July 2016 - 05:09 AM

Try changing the Accelerator Sensor. ( the gas pedal, the sensor is connected to it). I did and mine runs great now.

#30 SpartanAutoworx


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Posted 21 July 2016 - 10:44 AM

I buy around 100 chevy trucks a year so I am very familiar with this issue.


99% of the time the reduced engine power is due to the gas pedal. I always replace that first. 


Second is wiring going to the TB itself. Dorman makes a kit with a new harness and TB motor. I have never seen the motor fail but I have found two bad harness connections.

The third is the TAC Module on the firewall driver side. I have only seen a TACs Module fail once.


Replace the gas pedal and im sure all will be fine.

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