2006 Pontiac G6 GTP 3.9 V6
Question: Check Engine light on. Code WAS PO121. Took it to a shop to have it put of the diagnostic machine scan codes and I was told it was the Mass Air Flow which was replaced, ran good for about a week. The check engine light is on again and engine power reduced displays. I am know getting the following codes: P0121, P2119, P2135, WHERE WOULD YOU START AND WHAT WOULD YOU REPLACE FIRST?
Answer: Well, first off, I would not just start replacing parts. That will get expensive. All these codes refer to the throttle position sensors, which are part of the throttle body. First be sure to check all the fuses. There may just be carbon in the throttle, so clean that out good first with some carb cleaner. Then clear the codes and drive to see of that helps. If not, then you may have a bad throttle body assembly, a poor connection at the throttle, or a wiring problem in another place I have seen. There is a connector in the left side of the dash. Open the drivers door and remove the panel on the side of the dash.
There you will see a large connector with many wires in it. Unlock and disconnect that and look for corrosion or green on the terminals. This is the sign of water intrusion. This can give all these codes as well. If it does look corroded, you will need to clean it out and replace any terminals that look really bad. Then apply di-electric grease, then find and fix the water leak. Have seen this more on the Pontiac G6 with a sunroof- caused by a plugged drain, but it can also happen on a hard top, if the upper windshield is leaking.