09 tahoe has .1-.4 volt ground short on body of ecm

[Reecedakid03]

My 2009 tahoe 6 spd 4x4 has 230k miles, I’m having a short/over volting issue in the ecm circuit (have yet to test bcm or any other modules for ground issue) the ground side of my low fan relay has 12v on 1 of 2 ground prongs for that relay. Fans wont run until truck over heats which is what caused me to find this issue. I started poking away with my power probe and found the ecm ground is bad. The chassis of the truck has good consistent ground but the ecm body doesnt. I found the driver door may have a short (I’m guessing from a previous collision due to window regulator adjustment being loose) I rotate the rubber boot and the master switch stops working, so I thought it would be in the door, but I unplug the driver door harness from the module and a green wire is making my power probe freak out and show “P” and definitely isn’t a good circuit so I know it goes further than just driver door harness. I just bought a power probe ect3000 to try and diag more but didn’t know if anyone has had similar issues. The truck throws all kinds of codes for things that aren’t really bad it’s just bad ground or over volting. I have a topscan pro if anyone would like to see all the codes the truck has at the moment. All the grounds look good visually and tested with my power probe as well. One last thing, I double checked the ecm plugs have no corrosion. Any help will be greatly appreciated!!!

 

[kbuskill]

My 2009 tahoe 6 spd 4x4 has 230k miles, I’m having a short/over volting issue in the ecm circuit (have yet to test bcm or any other modules for ground issue) the ground side of my low fan relay has 12v on 1 of 2 ground prongs for that relay. Fans wont run until truck over heats which is what caused me to find this issue. I started poking away with my power probe and found the ecm ground is bad. The chassis of the truck has good consistent ground but the ecm body doesnt. I found the driver door may have a short (I’m guessing from a previous collision due to window regulator adjustment being loose) I rotate the rubber boot and the master switch stops working, so I thought it would be in the door, but I unplug the driver door harness from the module and a green wire is making my power probe freak out and show “P” and definitely isn’t a good circuit so I know it goes further than just driver door harness. I just bought a power probe ect3000 to try and diag more but didn’t know if anyone has had similar issues. The truck throws all kinds of codes for things that aren’t really bad it’s just bad ground or over volting. I have a topscan pro if anyone would like to see all the codes the truck has at the moment. All the grounds look good visually and tested with my power probe as well. One last thing, I double checked the ecm plugs have no corrosion. Any help will be greatly appreciated!!!

Just grasping at straws here, but i had an issue with the 5V reference signal voltage on several sensors and I found that the main harness coming from the ECM going over the top of the driver's side valve cover had a couple wires shorting out. There is a stud that sticks up from the valve cover/coil brackets and it had rubbed a hole through the wire loom and into a couple wires.

Just a thought and doesn't take much to give it a quick look.

In my case it kept throwing codes for knock sensors and I changed them but the problem persisted.

 

[Reecedakid03]

Just grasping at straws here, but i had an issue with the 5V reference signal voltage on several sensors and I found that the main harness coming from the ECM going over the top of the driver's side valve cover had a couple wires shorting out. There is a stud that sticks up from the valve cover/coil brackets and it had rubbed a hole through the wire loom and into a couple wires.

Just a thought and doesn't take much to give it a quick look.

In my case it kept throwing codes for knock sensors and I changed them but the problem persisted.

Awesome, thanks. I’ll give it a look!