Reecedakid03
TYF Newbie
- Joined
- May 28, 2025
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my 2009 tahoe has an extremely difficult short to ground issue, ill try to explain best i can. Ill start with ecm and front of truck side, the Lo fan circuit does not work even with fans commanded on but the high side works only if the truck overheats or is commanded on thru obd. the fan relay pins have an intermittent ground issue for the low fan relay. ive verified low fan does work and all connections and grounds on the front of the truck are good even the core support grounds. Ive swapped relays checked fuses w my power probe and even tore apart the fuse block and found a tiny bit of corrosion on the circuit board but didnt see any burn marks or damage so i cleaned it with alcohol and put it back in. The ecm itself has an intermittent ground/ voltage on the ecm body itself .1-.4V. ive swapped ecms 2 times and no difference. truck has false map and o2 codes as well. The alternator also puts out 15-16 volts on cold starts for some reason. ive checked all rear truck frame grounds and those are good. ive now added a ground cable from the ecm to the engine block, key on it grounds good but when running it has intermittent 0-.1 volt ground on my power probe, all the affected shorting circuits make my power probe sound like morse code is the best way i can explain it lol. i cleaned the engine block grounds up and battery terminals ofc too. the body of the alternator is good solid ground too.
the green pin 58 ecm wire is the one i tested with the battery neg disconnected and it still had 11.8 volts.
Interior side
radio harness has 1.8V on the bare ground wires (its a navigation/ theater unit) seat motors has .1 volts on the body of them, radio has static only with aux cord plugged in and changes with volume. using features (turn signals, interior lights, etc) make the headlights at night have a visible dim from the amp draw. ive disconnected seat harnesses and removed seats no change, disconnected body control module and no change, checked most interior grounding points aside from any under the carpet or in the rear of the vehicle and those are all good. the vcim has the intermittent ground issue from the body of it as well. ive unplugged the radio and amp fuses for 3 days to see if its a capacitor short but that made no difference. i see no evidence of a prior sound system being in the truck either. cigarette lighter ground connections are good. i unplugged all other control panels in the dashboard and that didnt change anything either.
if any gm electrical magician has any ideas pls help lol
the green pin 58 ecm wire is the one i tested with the battery neg disconnected and it still had 11.8 volts.
Interior side
radio harness has 1.8V on the bare ground wires (its a navigation/ theater unit) seat motors has .1 volts on the body of them, radio has static only with aux cord plugged in and changes with volume. using features (turn signals, interior lights, etc) make the headlights at night have a visible dim from the amp draw. ive disconnected seat harnesses and removed seats no change, disconnected body control module and no change, checked most interior grounding points aside from any under the carpet or in the rear of the vehicle and those are all good. the vcim has the intermittent ground issue from the body of it as well. ive unplugged the radio and amp fuses for 3 days to see if its a capacitor short but that made no difference. i see no evidence of a prior sound system being in the truck either. cigarette lighter ground connections are good. i unplugged all other control panels in the dashboard and that didnt change anything either.
if any gm electrical magician has any ideas pls help lol
