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Another Service 4WD in the Display

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I have 2 07 Duramax's. 

1 truck will show the Service 4WD fairly occasionally. To resolve I unplug the fuse and the 4WD will work. I sometimes do the "reset the transfer case procedure". I believe the i sue here is the Transfer Case Control  Module, I have a new one and waiting for warmer weather and replace.


Truck # 2 has never has had the 4Wd message. UNTIL I went through a car wash where they wash under the truck. 

Puling the fuse or doing the transfer case reset procedure fixed the issue. A snow storm was forecasted in 2 days and had snow and below freezing temps. So I took to the dealer.


The Dealer said Ground G103 was bad and needed repaired. They said this caused the transfer case motor to need replacing.

The Dealer corrected Ground G103 and replaced transfer case motor. So far all is good.



I always thought Ground G300 was the culprit for transfer case issues.



G103 is under the head on passenger side towards the front of the engine.

G300 is under the body mount by drivers side door.


Anyone else repaired G103 to resolve transfer case issues 


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well just rats- issue came back when the truck got wet again.

So yesterday, 4wd was working fine. Went through a car wash and just when they washed the underside of the truck, the Service 4wd came on.

I tried all the normal fixes, no luck.

I removed ground g300, under the drivers side door and cleaned it. the 4wd started working again. I used dielectric grease when attaching.

Then, I drove through a lot of water on the road due to melting snow, then the service 4wd came back on.

To recap: Cleaned ground g103 and g300. replaced the transfer case motor.

The issue is deferentially occurring when the front half of the truck undercarriage gets wet. 


Only guess I have is the axle actuator.

I cleaned the connectors at the motor and the speed sensor on the transmission near the transfer case  motor  and applied dielectric grease to these connectors as well.

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After a return visit to the dealer's shop. They discovered additional wiring chafing as the wires were routed over the fuel lines.


When i was at the car wash, during the portion where the undercarriage is getting washed. As the water spray passed under the firewall-dash area, the service 4wd light came on.


So hopefully the 3rd rounds of wiring repairs resolves the issue of the service 4wd light coming on when there is water involved.

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