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Old 08-17-2008, 08:39 PM
Join Date: Aug 2008
Posts: 1
Default engine power reduced light

I have a 2004 Z71 that runs great but as I am driving along at highway speed a light comes on and the truck only travels about 30MPH.It seems that it does not mater if the engine temp is at opperating temp or not.The engine is a 5.3 Liter gas and the problem started out just every once in a while and now it is almost all the time CAN SOMEONE SHED SOME LIGHT FOR ME
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Old 08-17-2008, 10:41 PM
shawnvw's Avatar
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Professional Mechanic
Join Date: Jan 2008
Posts: 2,571
Default RE: engine power reduced light

SES Light and Reduced Engine Power DTC P0120 P0220 P1516 P2135

2004-2006 Buick Rainer[/align][align=left]

2005-2006 Cadillac CTS-V[/align][align=left]

2003-2006 Cadillac Escalade[/align][align=left]

2003-2006 Chevrolet Avalanche, Corvette, Express, Monte Carlo, Silverado, SSR, Suburban, Tahoe, Trailblazer[/align][align=left]

2003-2006 GMC Envoy, Savana, Sierra, Yukon[/align][align=left]

2003-2006 Hummer H2[/align][align=left]

2005-2006 Pontiac GTO[/align][align=left]

Equipped with a 4.8 5.3 6.0 or 7.0 V-8 Engine[/align]


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.
[ol]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. [/ol]
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)

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Old 01-21-2010, 03:15 PM
CF Beginner
Join Date: Jan 2010
Location: Waukesha, WI.
Posts: 6

My 2003HD Silverado 4x4 with 6.0L gas engine, has the exact same problem as you described above. I wiggled the wiring, looked for bad wiring, etc. Truck still acts the same. I have now bought a new Throttle Actuator Control (TAC), and want to install it. The problem I am having right now with the replacement, is trying to remove the wiring connection without cracking/breaking the plastic connector. It won't come apart. How should it come apart without breaking anything? It is the only thing preventing me from finishing this replacement. Thanks in advance for any replies.
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Old 01-21-2010, 04:37 PM
CF Beginner
Join Date: Jan 2010
Location: Waukesha, WI.
Posts: 6

I just figured it out, after walking away from it for a few minutes, then coming back to it. At the top of the plastic wire loom connector that plugs into the TAC, there is a very small light grey colored plastic retainer, which prevents this connection from being pulled apart or vibrating apart while driving. First, take a small screwdriver, and carefully pry out this grey retainer, which exposes a small black tab. Second, press down on the small black tab, which releases it from the other half of the wire connection, which is part of the TAC itself. Caution Tip: There are two small hoses that look like vacuum hoses, that must be disconnected from near the bottom of the TAC, in order to fully remove the TAC unit from the engine. Those hoses are actually filled with coolant, and once you remove one of them, coolant will start pouring out, so have a couple of golf tees handy, to plug the ends of those hoses. I found out the hard way! I didn't know that coolant was in them, and a 1/2 cup of coolant spilled out, before I could find my golf tees in my toolbox. Oh, well.
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Old 02-09-2010, 09:06 PM
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Join Date: Feb 2010
Posts: 1
Default reduced engine power bs

I have the same problem with my 03 2500 6.0. I have been trying to figure this out now for about 20,000 miles. Some days it will drive all day with not a problem. Other days it will do it 5 time in a 50 mile round trip. But it has 140,000 miles on it and never a single problem with it til now. I will have to try what napco 57 said. I've read about some guys takeing there truck back to the dearler 2 & 3 times to fix this.
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Old 02-10-2010, 09:46 AM
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Join Date: Jan 2010
Location: Waukesha, WI.
Posts: 6
Default Follow up report.

It's been almost 3 weeks now since I replaced the Throttle Actuator Control, (TAC) unit, and that fixed it, because I have not had any more issues with it since. For those with this same problem, I have a tip to help get you by, so you are not stranded somewhere, with 'reduced engine power'. Try this, it worked for me: When your 'reduced engine power' light comes on, and you actually feel the loss of engine power. Pull over to the side of the road, and shut the truck off, make sure everything electrical is off. Wait about 15 sec., and then restart the truck. I'm guessing this must reset something, because the engine power should be fully restored, except the engine indicator light in the dash will stay lit. It will stay lit until the truck has been restarted after a few times. This doesn't permanently fix the problem, but it will get you back on the road right away, without being limited by only being able to go 25-30 mph, or having it towed. Thats only until the same situation happens all over again. Could be later the same day, or several days later, who knows?
(Once in awhile, I've had to wait a little more than 15 sec. before restarting the truck, in order for it to 'fix itself'.)
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Old 02-19-2010, 08:55 PM
CF Beginner
Join Date: Feb 2010
Posts: 2

I also have an 03 2500HD 6.0L Silverado. Same symptoms as you guys. What I was wondering is if you guys noticed the problem while in cruise control with the A/C on or not. I've noticed that the problem occurs more frequently when my A/C compressor is engaged then when its not. I brought it to a repair shop about 2 months ago and they diagnosed it as a throttle position sensor (TPS) the onr on the gas peddle. The truck acted up again about two weeks ago with A/C on and on a down hill grade foot off the gas. It just acted up again a few days ago with cruise control on down hill A/C on. Do you think the trottle body will fix this and should I get my old TPS back.

Please advise.
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Old 02-20-2010, 12:03 AM
wobblypop's Avatar
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Join Date: Jan 2010
Location: Smithers BC
Posts: 17

j megens, the a/c on or off shouldnt have any relation to your engine ecm, did the shop actually scan your truck for a dtc and if they did was it one of the dtc's that shawn vw posted on his bulletin? it very well could be that when they changed the tps that they moved around wires that maybe have an open or high resistannce etc... try following the wires from your tba and tps check connections for looseness when plugged in, look at the terminals for discolorations, or even if a terminal is pushed back further in the plugged than other terminals
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1986 silverado 350 35s
1986 wrangler 6.2L 3/4t 4x4
1969 firebird 455
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Old 02-20-2010, 12:13 PM
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Join Date: Feb 2010
Posts: 2
Default Reduced engine power

The shop did scan for dtc's and they believed the TPS replacement would fix the issue. I just figured that every time the vehicle went into reduced power mode it was always on a down hill grade, A/C on and my foot was off the gas, that the specific condition would help diagnos or pin point the problem. I will check the connections at the throttle body and at the TPS and later get the truck back to the repair shop so they can have time to look at the issue again.

Thanks for the info.
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Old 03-12-2010, 08:16 PM
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Join Date: Mar 2010
Posts: 2

I had the exact same problem for about 6 month. Took it to a shop this morning, and there were three wires off the throttle-body mount broken inside the insulation. The mechanic said it is common problem, and often not seen because insulation look good from the outside of the wires.
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Old 03-12-2010, 08:16 PM

2004, 2005, 2008, aveo, chevrolet, chevy, engine, impala, message, p2135, power, reduced, sliverado, tahoe, z71

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