Okay I have a 2006 GMC Sierra 2500HD 6.0 gasser with the electric throttle body. Code P1516 has been putting the truck into Reduce Engine Power mode. I am able to clear the code and the truck will drive great if I throw it into drive and go. Only until I come to a stop or let the truck idle that it will go into limp mode and that code will pop up. Every once in awhile it'll throw the code p2135 and p0220. All of which is throttle body related, after shutting the truck off for about 10mins and clearing the codes again only the p1516 pops up. I cleaned the throttle body and replaced the sensor on the side of the TB. I did notice that putting the tbps back on that it doesn't click in all the way, it will go on but not click in. I looked over all of the grounds which seemed good. Also the butterfly on the TB clicks back and forth when the truck idles right before it goes into Reduce Engine Power. Could this be more of an electrical problem rather than a throttle body. Also to note I did a relearn on the throttle body after taking it off and cleaning it.

You may need to get the latest calibrations with a PCM flash. Call around and find a shop that can update your PCM with the latest software.
Also, remove clean and tighten G103 and G104
104 has been the solution for a few fixes at Identifix.
Do you have the wiring diagrams?

These are all confirmed fixes.
84 - Replaced/Cleaned Throttle Body Assembly
23 - Replaced/Repaired Electronic Throttle Body (ETB)
9 - Repaired/Cleaned Ground G104
8 - Repaired Throttle Body Wiring
5 - Performed Throttle Body Cleaning Procedure
4 - Replaced Throttle Actuator Control (TAC) Motor
3 - Replaced Throttle Actuator Control (TAC) Module
3 - Repaired Ground 103
3 - Replaced Electronic Throttle Body (ETB) and Replaced Electronic Throttle Body (ETB) Connector
2 - Replaced Throttle Actuator Control (TAC) Motor Connector
2 - Tightened Battery Cable(*)
2 - Performed Powertrain Control Module (PCM) Programming
2 - Replaced Electronic Throttle Body (ETB) Connector
1 - Tightened Throttle Actuator Control (TAC) Module Connector
1 - Replaced Fuel Pump
1 - Replaced Throttle Position Sensor (TPS)
1 - Replaced Throttle Position Sensor (TPS) Connector
1 - Repaired Throttle Actuator Control (TAC) Module Ground Wiring
1 - Cleaned Fuel Injection System
1 - Replaced Electronic Throttle Body (ETB) and Performed Powertrain Control Module (PCM) Programming
1 - Repaired Throttle Body Connector Terminal(*)
1 - Performed Powertrain Control Module (PCM) Programming and Replaced Throttle Body Assembly
1 - Replaced Throttle Actuator Control (TAC) Motor and Replaced Throttle Actuator Control (TAC) Motor Connector
1 - Replaced Electronic Throttle Body (ETB) and Replaced Throttle Body Connector Terminal(*)
1 - Tightened Throttle Actuator Control (TAC) Module Connector and Tightened Throttle Actuator Control (TAC) Motor Connector
1 - Replaced Throttle Actuator Control (TAC) Motor Connector and Replaced Throttle Body Wiring
1 - Cleaned Connector H5
1 - Replaced Intake Manifold Gasket(*) and Replaced Throttle Body Assembly
1 - Cleaned Battery Cable(*) and Cleaned Ground 103 and Cleaned Ground G104
1 - Replaced Electronic Throttle Body (ETB) and Repaired Throttle Actuator Control (TAC) Module Ground Wiring
1 - Replaced Electronic Throttle Body (ETB) Connector and Replaced Throttle Body Assembly

When you cleaned the TB, did you take it out and clean thoroughly front and back with plate open and closed?

Yes I did, I gave it a good deep clean with a toothbrush and throttle body cleaner. It open and closes as it should by hand. I took it back off earlier and when I turn it side to side I can hear a noise inside of the throttle position sensor on the side of the TB. As if the gears are moving freely, also during some wire and connector inspection on the TAC one of the connections crumbled when I went to take it off of the TAC. So I'll be replaced the harness as well.

Already thank you, no I don't have the wiring diagram, but I'm sure I can look at up. Thanks again.

Already, took the TB until off and was able to hear the gear freely move inside of the TPS. Took that off and the gear can easily be removed. So I am guessing ok have to replace the whole unit.

Clean these grounds.
2 and 4

#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) 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 EngineThe following diagnosis might be helpful if the vehicle exhibits the symptom(*) described in this PI.
Condition/Concern: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.
Recommendation/Instructions: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)

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.
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Update.... After replacing the throttle body unit the truck no longer goes into Reduce Engine Power and no more codes.