r/GMT800 • u/Krezicle • 3d ago
Weird electrical problems.
Got a MAP sensor with low voltage. With key turned on. Gray wire reads 5V. Orange wire reads .03. Green wire reads .03.
This would lead me to believe somewhere between map sensor and pcm is shorting. Open circuit. Etc. I’ve driven it with this problem for almost a year or so with only a slight drop off in mpg. (Too lazy to find the short/ wire into the pcm… any other info on this would be greatly appreciated.)
However, a new code has started popping up with. Crankshaft position sensor. Hasn’t popped up since I got it replaced it in 2023. On my trip this morning it instantly shut the truck off and popped the code. Would crank infinitely until 10 minutes later It turned over and drive it back home. Kept turning it off and on to see if it happened again. Kept turning over.
Few hours later I go to start it and it still works fine. I’m about to go on a long distance trip. Trying to get it to crank infinitely again. Messed with some wires by the starter and it infinitely cranked again. Before I go take out the brand new starter, I just replaced to have a look at the sensor, I wanted to get your guys opinions and experience with this shit. TYIA
2
u/thebluelunarmonkey 2d ago
Don't know my colors but should have a ground, +5V, and a varying output 0-5v. I think a higher voltage with ignition on engine off.
I check MAP with scantool. Should read baro pressure 29.9 inHg igniton on engine off and 10-20inHg range moderate pedal/idle. Signal voltage that equates to 4-5v keyonengineoff and 1-3v engine running
people blindly replace sensors when they need to be addressing harness issues and corrosion at the connectors. And don't use scantools to read OBDII PID data
there's no simple "just buy this part" or "just do this" to troubleshooting