I brought my car to my auto tech school and when i hooked up the OBD2 reader to check my sensor reading, all the reading were hopping around( ex; MPH= 0 then 89, 150 etc.) and the engine was off. I asked one of my teachers is it a connection or a bad PCM and he told me odds are the ground isn't connected. How can I test for this or look for it and can the PCM be working right?

 

well if hte PCM wasnt grounded the car wouldnt even start because the PCM wouldnt have power. All I can suggest is to check your cables to your PCM and ensure all the pins are all the way into the plug harness. there are a few different grounds in the plugs of the PCM.

ORRRR what It could be is some of the SCAN TOOLS have whats called a DEMO MODE before you actually connect to the car..........might wanna check and make sure your professor isnt a moron 1st before you go tearing into a "GHOST PROBLEM"

In any event, your car runs fine right?.......dont fix what isnt broken.

 

Most professors are morons because they get too full of it, but some are acctually smart, just because he's a professor doesn't mean he's right, & to automaticly say its a GROUND to PCM is being too confident & gurranteed he's wrong if he thinks he can tell a ground from a bad signal wire LOL.

Anywho the PCM has a main ground, on the passenger side of the block just above the starter & below the header (#6 primary) there is a black thin wire attached by a small 10mm stud or so, that is the main PCM ground, check it, I would suggest taking it off, cleaning it & reattaching it.

Not all sensors feed off that ground, thats strictly for the PCM, beside the battery there is a bunch of grounds there, take them off, clean them & reinstall, then on the driver's side cylinder head by the ignition coil there is a bunch of sensor grounds there aswell, disconnect those, clean them & reinstall.

Hope this helps.

matt.

 

That makes perfect sence, my car was acting bad/ sounding bad like it had a missfire only after my spark plug wires were put in. Think the ground could have been pulled out in the process of doing the plugs?

 

might have, or you might have the wire arcing onto the ground if its not properly on the plug, its a pretty ****ty place to put a ground for the pcm I must say lol

 

Does anybody have a diagram that lists all the grounds and their locations?