Hi, new to the forum. 2003 Trailblazer, 168,000 miles. Truck's SES/REP lights came on right after leaving work the other day. Towed it home and scanned it. P0107 and P0105. Thought the MAP sensor was bad. Replaced it in haste w/o doing any diagnosis. Cleared codes and P0107 came right back with SES/REP lights. Checked wire harness with key on and no 5v at the gray wire. Good ground on Orange/Black. I've heard that this harness goes directly back to the computer. I cut the gray about 18 inches back (thinking the wire may have been damaged) where it enters into the looms and checked for voltage again there. Nothing. Battery is good and even checked with another brand new battery. After more inspection, I realized that the CPAS was covered in oil and when I pulled the plug off, the connector was filled with oil. I've replaced the CPAS and thoroughly cleaned the harness. Cleared codes and checked again. Same thing. P0107 and lights came right back on after clearing codes. If there is supposedly nothing wired between the MAP and the computer, could this be a computer issue? If the throttle body was bad, could that be it? I just cleaned that about 3 months ago and it looks clean. I'm stumped. Thanks in advance for any help.

 

If the engine is not in good condition, is missing, has poor fuel pressure, or has an internal issue with the engine like a burned valve, these things can prevent the MAP sensor from having a correct voltage output. The ECU could also be bad but that is rare. Make sure the wiring is OK.

 

Oilcanhenry, thanks for the reply. The vehicle has been running great until this and has never had SES/REP light come on in the several years I've owned it. Like I said, I was leaving work when this happened. Started the truck, just took off and got a minor sputter, then the codes and limp mode. I'm confused by what you mean by "voltage output". The problem, to me, seems to be the voltage input from the PCM to the MAP sensor or am I just not understanding its function correctly.

As far as the previously mentioned 5v reference wire (gray) for the MAP, I still cannot find a break. I obtained a wiring diagram with labels of all the pin connectors for all 3 wiring harnesses at the PCM and checked every gray wire against the MAP harness gray for continuity and got none on any of them. I'm assuming that the power (5v) not getting to the MAP sensor is the root problem. Especially based on the P0107 code I'm getting. I guess at this point I am going to have to unwrap all the electrical tape and loom to chase the MAP gray wire all the way back to one of the 3 harnesses at the PCM unless someone either knows exactly which pin connector on which harness is the MAP gray or knows of a better way to proceed.

Any suggestions welcomed. Thanks!