I removed my truck's throttle body to clean it and after reinstalling it the Reduced Engine Power light came on and the truck would only idle. I had no throttle response at all. I have a code reader and I got P120, P220, P1516, and P1518. After doing a lot of research I found that these DTC's are a pretty common issue with GM trucks. The P120 and P220 codes point to the TP 1&2 sensors and the P1516 and P1518 seem to point to wiring harness issues. I found information on how to test the TB (Voltage and Resistance measurements) and all measurement seem OK.
I checked the wires on the connector that plugs into the TB and found no broken wires (another common issue with GM) I wiggled the harnesses and nothing changed.
I have checked all the ground associated with this (especially S103) and they are tight. Battery is brand new.
I have found that I can clear the DTC's, and without starting the engine, shut off the ignition, turn the ignition back on (without starting the engine) and all 5 of the above mentioned DTC's will appear. I have also found that I can clear the DTC's and then start the truck and if I give it gas right away I get normal throttle response and as long as I keep it above 1000RPM's it runs normal. As soon as I let it idle the REP light comes back on and all 5 of the DTC's are present. I have done this process 3 times and got the same results each time.
I found that the 5V Reference to TP Sensor 1&2 goes to 0V (one or the other, not both) most of the time when I get the DTC's. Grounding either of these wires will cause them to go to 0V. Turning the ignition off and then back on will reset them to 5V.
From what I have read there have been cases where GM itself admitted to not knowing root cause. I've read horror stories about folks that have spent thousands of dollars and still have this problem.
I would be great if you could give me some advise as to what the problem might be, I would really appreciate any time you could give me.
Thank you very much,
have the same problem?
Thursday, September 5th, 2013 AT 11:08 PM