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GMTechBernard, Shop Foreman - GM World Class Tech
Category: Chevy
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Experience:  GM
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what does reduced engine power light coming on mean

Resolved Question:

what does reduced engine power light coming on mean
Submitted: 7 years ago.
Category: Chevy
Expert:  GMTechBernard replied 7 years ago.
Hello! My screen isn't showing the year/make/model/engine of what you are working on. If you could please post back with that, it would help! Thanks!
Customer: replied 7 years ago.
2002 chevy avalanche 350 I think
Expert:  GMTechBernard replied 7 years ago.

Thanks, Billy.


With your vehicle, you have an electronic throttle. There is no throttle cable going to the pedal. the system consists of an accelerator pedal with sensors, a throttle plate with attached motor and sensors and a module in the middle that ties the two together.


Whenver the module sees an issue with the electronic throttle, the accelerator pedal or the module itself, it goes into Reduced Power mode. When in reduced power, you are basically limited to idle, sometimes you can cut the key off and restart and it will be fine again until the fault is seen again.


There are several reasons why this light may come on, and the best way to know for sure why, would be to have the system scanned for Diagnostic Trouble Codes (DTCs). this will indicate if the fault was with the Throttle, Pedal or internal module issue. I can tell you from experience that most faults are with the throttle body and/or connector.


As a matter of fact, here are a few bulletins from GM regarding the more common causes:


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.

  1. 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.
  2. 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.
  3. 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)



Customers may have a concern of lack of power and engine light on. DTCs set will almost always contain a P1518 and may contain any of the following (P1516, P2108, P0220, P0120, U0107). An improperly torqued TAC module ground may be at fault. The Ground is listed as G104 on TAC module schematic which is incorrectly labeled on SI document ID 855376. The correct ground is G103. The locator for SI states that G103 is located on the left hand side which is incorrect. However, there have been field reports stating that G104 has also corrected this condition. G104 is a horizontal bolt in the rear of the left head and extremely difficult to reach. G104 should also be tightened at the same time.

There have also been field cases where ground G110 on the outer drivers side frame rail caused a P1518 code and an intermittent connection at splice 102 on the intake.

All published SI diagnostics should be followed in addition to following the recommendation listed.


Tighten ground G103 located behind the right cylinder head (passenger side) just below the head and mounted into the block. The ground uses a 13 mm bolt head mounted vertically to the engine block just above the bell housing.




These are things you can do yourself. If nothing turns up, please have it scanned for codes before you purchase any parts!


Please let me know if you have additional questions!

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