Vehicle: 2013 GMC Sierra 2500, 4WD, V8-6.0L, Automatic Transmission/Transaxle

Mileage: 86,910

Problem: The customer complained that the engine in his truck had no power to climb hills or pull out into traffic. The malfunction indicator light (MIL) was not on.

Case Details: The technician connected a scan tool anyway just to see if there were diagnostic trouble codes (DTCs) anywhere. There were none. Next, he went on a road test and noticed the engine was low on horsepower. Something else he noticed was a rattling sound at the right rear side of the engine. It almost sounded like a catalytic converter had broken apart inside and had plugged the exhaust.

After inspecting the catalyst and finding no issues, he checked out the starter. He found that the starter drive was staying engaged. The spring had broken on the starter solenoid and was not retracting the drive gear back in.

The reason it lacked power was because the knock sensor picked up that noise and retarded the timing. The powertrain control module (PCM) thought the engine was pinging.

Confirmed Repair: The technician replaced the starter, and the engine ran as it should. Problem solved!