2009 tahoe fan and pcm grounding issue

[Reecedakid03]

Got an 09 tahoe w an e38 computer. 5.3/6l80e truck and the e fans will not turn on unless commanded thru scanner or truck overheats. The connectors are in good shape but have no power or ground on dr side fan connector and only ground on pass side fan connector. All relays are good and fuses I’ve tested and swapped it all. PCM body has intermittent ground signal according to my power probe and didn’t know if anyone has had this issue before. I’m thinking pcm is bad but Cant find any culprits, any help would be appreciated! Truck has codes that aren’t really issues as well. Map sensor and o2 codes yet they all read and are fine. I’ve replaced the map with a gm genuine sensor and code still shows.

 

[Big Mama]

Have you checked the battery and other ground connections? My problem was the one by the passenger foot well and I had some frayed wires under the driver sill plate that went to the B pillar ground.

 

[Reecedakid03]

Have you checked the battery and other ground connections? My problem was the one by the passenger foot well and I had some frayed wires under the driver sill plate that went to the B pillar ground.

Battery is good. But I did notice if I turned the wire boot on the inside of my dr door the switches stop working maybe it’s a short in that harness but idk how that would bypass all other chasis grounds unless it’s enough to make all the grounds have voltage

 

[mikez71]

No fan wiring in door, perhaps a separate problem?

Looks like the fans use ground zone #1 & #2, which look like both front corners, maybe somewhere by radiator support? idk..

 

[Fless]

From what I can tell the fans use G100 and G101. See the links below from www.charm.li. Verify your vehicle info before using these diagrams.

Cooling System — 2009 Chevrolet Tahoe 2WD V8-5.3L Service Manual | Operation CHARM

Detailed repair manual for the 2009 Chevrolet Tahoe 2WD V8-5.3L.

charm.li

Locations are #6 and #8:

G100 — 2009 Chevrolet Tahoe 2WD V8-5.3L Service Manual | Operation CHARM

Detailed repair manual for the 2009 Chevrolet Tahoe 2WD V8-5.3L.

charm.li

 

[Reecedakid03]

Found the coolant temp sensor wire has the same intermittent ground issue as well

 

[Reecedakid03]

From what I can tell the fans use G100 and G101. See the links below from www.charm.li. Verify your vehicle info before using these diagrams.

Cooling System — 2009 Chevrolet Tahoe 2WD V8-5.3L Service Manual | Operation CHARM

Detailed repair manual for the 2009 Chevrolet Tahoe 2WD V8-5.3L.

charm.li

Locations are #6 and #8:

G100 — 2009 Chevrolet Tahoe 2WD V8-5.3L Service Manual | Operation CHARM

Detailed repair manual for the 2009 Chevrolet Tahoe 2WD V8-5.3L.

charm.li

Thank you much!!!

 

[Reecedakid03]

No fan wiring in door, perhaps a separate problem?

Looks like the fans use ground zone #1 & #2, which look like both front corners, maybe somewhere by radiator support? idk..

View attachment 472951

View attachment 472952

Thank you for the help!

 

[Fless]

Found the coolant temp sensor wire has the same intermittent ground issue as well

That could be the connector or the wiring pigtail, or maybe a main ECM ground. Both connections at the ECT are to/from the ECM, with no external grounds.

Third diagram at this link:

Electrical Diagrams — 2009 Chevrolet Tahoe 2WD V8-5.3L Service Manual | Operation CHARM

Detailed repair manual for the 2009 Chevrolet Tahoe 2WD V8-5.3L.

charm.li

 

[Reecedakid03]

That could be the connector or the wiring pigtail, or maybe a main ECM ground. Both connections at the ECT are to/from the ECM, with no external grounds.

Third diagram at this link:

Electrical Diagrams — 2009 Chevrolet Tahoe 2WD V8-5.3L Service Manual | Operation CHARM

Detailed repair manual for the 2009 Chevrolet Tahoe 2WD V8-5.3L.

charm.li

all wiring ive seen looks good ive pulled the ecm off and checked the pins for corrosion etc and the fan connectors as well. i pulled off my front bumper and checked the grounds on both lower core support mounts and those have good consistent ground signal and checked all other engine grounds. when key is off all grounds are good. im thinking its the ecm maybe prev owner shorted it doing a battery swap but could i try grounding the coolant temp sensor wire maybe or would that short my ecm worse. ecm has consistent .5 volts on the ecm body itself while running though. not sure where the ecm grounds tho ive searched through diagrams and cant find it

 

[Fless]

Verify that I selected the correct vehicle. The main ground for the engine computer is G103:

Electrical Diagrams — 2009 Chevrolet Tahoe 2WD V8-5.3L Service Manual | Operation CHARM

Detailed repair manual for the 2009 Chevrolet Tahoe 2WD V8-5.3L.

charm.li

G103 is on the passenger side of the engine - unless it's been moved for one reason or another; I can't tell if it's on the head or the block, but here's the link to the pic (see the comment about RPO HP2):

G103 — 2009 Chevrolet Tahoe 2WD V8-5.3L Service Manual | Operation CHARM

Detailed repair manual for the 2009 Chevrolet Tahoe 2WD V8-5.3L.

charm.li

 

[Big Mama]

Mine was on the block.

 

[Reecedakid03]

Verify that I selected the correct vehicle. The main ground for the engine computer is G103:

Electrical Diagrams — 2009 Chevrolet Tahoe 2WD V8-5.3L Service Manual | Operation CHARM

Detailed repair manual for the 2009 Chevrolet Tahoe 2WD V8-5.3L.

charm.li

View attachment 478019

G103 is on the passenger side of the engine - unless it's been moved for one reason or another; I can't tell if it's on the head or the block, but here's the link to the pic (see the comment about RPO HP2):

G103 — 2009 Chevrolet Tahoe 2WD V8-5.3L Service Manual | Operation CHARM

Detailed repair manual for the 2009 Chevrolet Tahoe 2WD V8-5.3L.

charm.li

I’ve found the intermittent ground/.1- 2v signal on the radio harness, seat harness, relay control circuit that controls all engine grounds. If I unplug the neg battery terminal my fuse block still has 11.3 volts so something with a capacitor is back feeding short to to ground only with key on. The vcim has the ground issue as well. Body control module isn’t affected though. There’s all chasis grounds are good and no interruption other than the few left under carpet and seats and maybe in the rear of the Tahoe. Strongest short voltage I’ve gotten is on the radio harness where I saw 1.8 volts rather than the typical .1-.4