This 2007 GMC Yukon came in with multiple complaints among which were the engine seemed to have no power, the Service Engine Soon, ABS and Traction lights were on and there was a stability message displayed in the Driver’s Information Center (DIC). The customer also stated that the vehicle ran fine sometimes but as soon as the warning lights and messages came on it would just barely run. The condition had been getting worse and now they were afraid to drive the vehicle. They had recently purchased this vehicle as is and had no history to go with the vehicle. They had only been able to drive this Yukon about 300 miles since they purchased it.
Although they had stated that no one had been able to retrieve any fault codes, I had no problem retrieving these. This vehicle’s codes were P0300, P0352, P0354, P0356 and P0358 it could have just as easily have been codes P0300, P0351, P0353, P0355 and P0357. You will see why later in this article.
Since the P0352, P0354, P0356 & P0358 codes have to deal with the coil control circuits for all of the bank two ignition coils, I started by checking the basic power and ground supplies to the bank two ignition coils. There was no problem with the voltage signal on the red wires at the harness terminal position “A”. Checking the ground circuit on the black wire at the harness terminal position “D” yielded a varying voltage reading of between .120 and 6 volts depending on how well or how poorly the engine was running. When the ground signal was relatively okay at .120 volts the engine would run okay. As the voltage on this wire rose the engine would start running worse. As a quick confirmation test, I piggybacked a good ground into this circuit to prove that repairing the faulty ground would indeed fix the customer’s complaint.
After looking at a wiring diagram I noted that the ground wires for the bank one and bank two ignition coils terminated at the ground position G200 located at the lower left front side of the engine block. I opened the harness loom just behind the alternator assembly and looked for the two black wires. It turns out that there are quite a few black wires located in this harness. Most were very small (18-22 gauge), two were 16 gauge and there was one 10-12 gauge wire. I surmised that the two 16 gauge wires were likely the ground wires for the bank one and bank two ignition coils. Testing found a good ground signal on one and the same faulty signal on the other.
The problem has to be closer to the ground point G200. The ground point G200 is located at the lower front side of the engine block on the driver’s side of the engine. It is located behind the gray plastic harness retainer that attaches to the stud.
The exterior surfaces of the stud were heavily rusted.
The mating/contact surface was clean.
Moving the wires around found a broken wire at the ring terminal that has two wires attached to it.
I had to disconnect more of the wiring harness going back to the rear of the engine so that I could bring the harness out far enough to make proper repairs.
In the end I would wind up having to cut back quite a bit of wiring to find good clean wire. I replaced the wiring for both of the terminals that attach to the G200 location.
The heat shrink tubing I use has a meltable liner but I chose to use some extra sealant where the two wires go into the splicing terminal. Note how I place the sealer approximately where the heat shrink tubing will end. I use a sensor safe rtv sealer/gasket maker that I have tested and have not found a problem with it reacting to copper wire.
The heat shrink tubing slid up and over both the crimped splicing terminal and the sealant.
Shrinking the tubing in place forces some of the sealant out which is what I wanted.
Now it is just a matter of laying the harness back in place and tightening everything back down.