I have a 2005 SV6. when it is cold outside the engine light comes on then Reduced Engine Power comes up on the display. After letting the van warm up to operating temp. I shut it off then restart. Engine light stays on but van is no longer in Reduced Engine Power mode and I can drive it.
I get the following codes: p1516, p2101 and p2135.
Any help would be greatly appreciated.

This has been a bugaboo for GM engines with the TAC system.....

When the code sets, the CE light comes on, and in some cases you have reduced engine power.......


There are a few things that the average guy can do to check this out......one, a dirty throttle body bore, can cause the throttle plate to stick/bind......so clean the throttle plate and bore...in addition, after cleaning the bore and letting the motorized plate snap into position and verifying it'* not sticking/binding, with key out of the ignition and nothing on, disconnect the neg cable first and then the pos cable.......then hold both cables together for a minute....then attach pos, and then the neg battery cable.....what this does is reset all the modules.....should also clear all codes(code reader/scan tool)

Second, check the harness to the throttle body module....make sure all female connectors are tight and not "spread".......need a male connector to do a "drag test" on each female connector....next is the harness itself......a wire can break inside it'* insulation causing intermittent conditions......flex each wire 5-8 inches from the end of the harness connector, to "feel for a possible break....there have also been some "ground" problems......check the ground for this circuit....it'* position varies with the engine it'* on....

If all that checks out, then it'* a possible throttle body.......also, the vehicle should be checked for possible updates concerning programming for the TAC system......

Almost kind of impossible to check this out without wiring diagrams and a TECH II.....

Thank you for your response. Yesterday I cleaned the throttle bore and plate and cleared the codes using the steps you suggested. This did cause the CE light to go out. Today when I started the van same problem. I did check the harness for corrosion, all looked OK. I will check for broken wires / spread connectors next.
I find it funny that it only happens when it is cold.
The problem started early last spring when the temp. outside was still cold. I checked the wiring harness through the floor at that time, after that the problem went away. I assumed the problem was corrected but looking back the weather improved and it warmed up. Van was OK all summer then started acting up again only when the temp. began to drop in the fall.

Like I said, hard to diagnose without wiring diagrams and a Tech II.....you have the throttle body module, the ECM, the pedal position sensor, and all the wiring in between each element.....does it sound like this system is better than a cable and a TPS sensor? Not to me....another attempt at trying to build a better mouse trap....and when you have different manufacturers building these systems as cheap as possible, especially wiring wise, give me the old system any day....

Hes right on with the cheap manufacturing process. Gm needs to learn not to use wire terminals designed for computers to put into vehicles. Terminal fretting and loose crimp connections are one of their biggest failures.

If GM did this we mechanics would be out of a job