Vehicle: 2009 GMC Sierra 2500, 4WD, V8-6.0L, Automatic Transmission/Transaxle

Mileage: 226,562

Problem: The customer said that the engine keeps running when he turns the ignition key off. Everything else shuts off except the malfunction indicator light (MIL), and the engine continues to run.

Case Details: The tech working on the truck noticed that if he removed the powertrain relay, the engine didn’t shut down either, so he called ALLDATA Tech-Assist.

The consultant recommended checking to see if the ECM-IGN fuse #56 was still powered up with the ignition off. If it was, he advised pulling the Run/Crank relay and checking it again. If fuse #56 was still powered, it was possible that another fuse was feeding back into the circuit.

Fuse #56 was still powered after pulling the Run/Crank relay, so the tech began pulling fuses one at a time to determine which one would cause the voltage to disappear from fuse #56. He began by pulling fuse #19, then #43, #48, #54 and #40. He noticed that when he pulled the Air Bag fuse (#40), power to fuse #56 disappeared.

The Air Bag module is powered up by fuse #40 so he decided to inspect the module. The air bag module, which is located under the seat, showed signs of corrosion on the case.

Confirmed Repair: The tech replaced the air bag module and programmed it. After that, the engine shut down normally. Mystery solved!