With ATSG having the opportunity to help shops solve problems, sometimes we get faced with some real doozies. A shop will call and give us a laundry list of DTCs, leaving us to think someone must have a bulkhead connector unplugged. We then go through the arduous task of deciding which codes prompted other codes to set—we’re actually diagnosing diagnostic codes themselves at that point. So, when an issue comes up on our help line with codes that actually tell the story, it makes for a nice change, as well as a quick pathway to a repaired vehicle.

This is what happened with Gary and Matt at Goffnet Transmissions. They called in with a 6L80 in 2011 GMC Yukon 5.3L 4WD that would blow fuse 19 as soon as the ignition was turned on. Fuse 19 is a Trans Ignition 1 circuit, which caused code P2534 to set. With the transmission harness unplugged, the fuse would still blow. It was then that they consulted a wiring diagram to see everything that is on the Ignition 1 circuit. Figure 1, above, is a partial wiring diagram which reveals that this Trans Ignition 1 power supply also goes to terminal C in the Front Drive Axle Actuator. 

In fact, code C0379 was set for this actuator. Not much thought was originally given to this code but now that it is tied into the same fuse circuit, it has become an actuator of interest. Once it was located, they unplugged it and discovered that it was loaded with gear oil (see Figure 2). 

The actuator had failed in such a way that fluid from the front drive axle seeped through it and loaded the connector causing the short in the circuit. To verify that this was the case, the actuator was left unplugged, and a new fuse was installed. When they started the vehicle, the fuse didn’t blow. So, these two codes told the whole story! Once a new actuator was installed, the vehicle was delivered to the customer. Job done.

Read more stories from our Technically Speaking column series here.