2003 GMC Sierra 5.3L (has 2004 engine) Drive by wire. Reduced engine power (Limp Mode). Following error codes - P1516, P2135, P0120. Checked all connections at throttle body(Wiggle tested the individual throttle body circuits). Not duplication of problem. Checked connections at black box on fire wall, etc. can not duplicate problem. The truck goes into -Limp- mode in the morning on the way to work every day, I let truck sit for a few minutes, turn key on and off couple of times and I'm back in action for the rest of my drive, does not happen again until truck has sat all day at work and then on way home goes back into -Limp mode- HELP!!!!

It is more then likely a wiring problem or Throttle position sensor or the electric motor in the throttle body ! Pt 2 2007 Chevy 2500HD Reduced Engine Power Warning Fault Code P1516... Drive by Wire Function and Diagnostics by Wells

P1516 is a reduced engine power code ,check the ground wire to the head and have your throttle position sensor (TPS) tested

P0894 Transmission Slipping
P1258 Engine got Hot
P1516 Throttle Actuator Control (TAC)

Chevrolet Tahoe vehicles may experience a performance issue where they will not go over 15MPH. The vehicle may appear to be in "limp-in" mode, giving just enough power to get you to a shop. The codes indicate a problem with the throttle position sensor circuits and throttle actuator performance. Do NOT start replacing parts. Shops report a pattern failure in the electrical harness to these sensors. Chevrolet has issued a revised replacement harness to correct the problem. The original connector was prone to vibration and broken wires that disrupted the signal to the PCM and put the vehicle into reduced power mode.

Most of the time with the 5.3L in the GM vehicles it is a problem with the Throttle body for P1235 code. Usually you can pull the air intake off the throttle body, take a rag with some break cleaner and open the plate. Clean the inside of plate and throttle body. I will probably be Black Gunk build up that comes off. Just clean it really well. The sensor between the pedal and the throttle body have match signals. If one is off then it goes into reduced power mode. So this can be caused by this residue build up. It usually will fix your issue. It can come back but it will get you back on the road and help take you out of limp mode or reduced power mode.

1. This engine uses the Throttle Actuator Control (TAC) system. Thoroughly clean the throttle bore and throttle plate.

2. Inspect the air intake system for a missing or contaminated air filter

there is also a tsb on it TSB 07-06-04-003 for p1516 that involves replacing the pcm

Subject:LSJ, L61, LK5, L52, LL8 Engine -- Reduced Engine Power, MIL/SES Light, DTC P1516, P2135, P2138 (Replace PCM)

Models:2005-2006 Chevrolet Cobalt, Cobalt SS, Malibu
2006 Chevrolet Colorado, TrailBlazer
2006 GMC Canyon, Envoy
2006 HUMMER H3
2005-2006 Saturn ION, ION Red Line
2006 Saab 9-7X
with ECOTECTM 2.0L, 2.2L I-4 Cylinder Engine (VINs P, F-- RPOs LSJ, L61) or
VORTECTM 2.8L I-4, 3.5L I-5, 4.2L I-6 Cylinder Engine (VINs 8, 6, S -- RPOs LK5, L52, LL8)



Attention: The following bulletin information is only to be used if the customer has returned for REPEAT repairs for DTCs P1516, P2135 and/or P2138.



Condition

Some customers may comment on engine operation in the Reduce Engine Power mode with the MIL/SES light illuminated. This condition may be repeated and upon investigation, the technician may find the following DTCs set as current or in history:

• DTC P1516 Throttle Actuator Control (TAC) Module Throttle Actuator Position Performance
• DTC P2135 Throttle Position (TP) Sensor 1-2 Correlation
• DTC P2138 Accelerator Pedal Position (APP) Sensor 1-2 Correlation
Cause

This condition of a repeat DTC P1516, P2135 and/or P2138 may be caused by an internal concern with the PCM.
Correction



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Important: DO NOT replace the APP sensor. Inspect the PCM build date first.

Before following the diagnostic information in SI on DTCs P1516, P2135 and/or P2138, an inspection of the PCM serial number year and Julian (PCM build) date will be necessary to determine if the PCM will need to be replaced to correct the repeat DTC P1516. Refer to Engine Control Module Replacement in SI in order to remove the PCM. Refer to the above graphic illustration (1) for the location of the PCM serial number.

The serial number is read left to right. The last digit of the year is the 9th character and the Julian date is comprised of the 10th, 11th and 12th characters and is used to determine the PCM build date. Refer to the example below to read a build date from the PCM serial number:

* 8 6 Y N AU K 1 5 3 2 5 0 R P N *

If the PCM year and Julian dates are between 5182 and 5304 , replace the PCM. Refer to the Part Catalog to order the correct PCM for your vehicle application, if necessary.

Vehicles with PCM built outside the dates should refer to SI diagnostics for DTCs P1516, P2135 and/or P2138

You need to have an OBII scan(fault scan) - to identify what sensor triggered computer (light) Reduced Engine Power = rig is in "Limp" mode. So you can drive it to get to repair shop.

DTC P0120 P0220 P1516 P2135 these should be the problem codes.
2003-2006 Chevrolet Avalanche, Corvette, Express, Monte Carlo, Silverado, SSR, Suburban, Tahoe, Trailblazer. for reduced engine power. p0120 is throttle position sensor, ( tps ). p0220 is relates to tps, p1516 tps is out of range. p2135 is a throttle body code, the throttle body needs replaced. but before you do it replace tps first to see if it takes care of the other codes. have a good day !!

Pt 1 2007 Chevy 2500HD Reduced Engine Power Warning Fault Code P1516...

P1516 Throttle Actuator Control(TAC) Module Throttle Actuator Position Performance

This is your problem and should be taken in to chevy for repair

AUTO DASH SAYS 'REDUCED ENGINE POWER" TRANSMISSION FLUID SEEMS OK AND COOLANT OK. WHAT ELSE COULD IT BE?