There are 3 owner-reported engine complaints for the 2012 GMC Sierrain NHTSA's database. These are unverified consumer reports and may not reflect confirmed defects.
ENGINE WILL INCREASE IDLE FROM 700 TO 900 AT ANY TIME. ONE CAN BE SITTING AT A TRAFFIC LIGHT AND IT MIGHT INCREASE OR DECREASE. I PULL A 5TH WHEEL (35 FEET) AND IT IS VERY DIFFICULT TO STOP WITH THE ENGINE TRYING TO KEEP GOING. ALSO IT IS VERY SCARY TO STOP ON SLIPPERY ROADS. THIS DID NOT START UNTIL THE VEHICLE HAD APPROX. 35,000 MILES ON IT. THE DEALER TELLS ME IT IS NORMAL, BUT I HAVE TALKED TO OWNERS OF THE GM DIESEL FROM MODEL YEAR 2008 THROUGH 2015 AND NONE OF THEM HAVE THIS CONDITION. *TR
THE FUEL INJECTION PUMP CP4 HAD A CATASTROPHIC FAILURE AS I WAS DRIVING ON A HEAVILY TRAVELED FOUR LANE HIGHWAY, US RT.20. I LOST POWER STEERING AND BRAKES. I FELT FORTUNATE THAT I WAS NOT TOWING A 16,000 LB. FIFTH WHEEL CAMPER DOWN A MOUNTAIN ROAD.I SAY THIS BECAUSE IT WAS EXTREMELY DIFFICULT TO MAINTAIN CONTROL OVER THE TRUCK STEERING IT AND BRINGING IT TO A CONTROLLED STOP. I HAVE READ ABOUT THESE PUMPS FAILING ON NUMEROUS DIESEL FORD AND GM TRUCKS. I ALSO FEEL IF A WOMAN OR SMALL PERSON HAD THIS HAPPEN TO THEM THE OUTCOME COULD END IN LOSS OF CONTROL RESULTING IN INJURIES EVEN DEATHS. THE ONLY ONE THAT KNOWS THE ACTUAL NUMBER OF PUMPS THAT HAVE FAILED IS THE MANUFACTURERS, WHO WILL NOT SHARE THAT INFORMATION WILLINGLY. *JS
TL* THE CONTACT OWNS A 2012 GMC SIERRA. THE CONTACT STATED THAT WHENEVER THE VEHICLE WAS IDLING THE CONTACT NOTICED THAT THE VEHICLE WOULD VIBRATE WITHOUT WARNING. THE VEHICLE WAS TAKEN TO THE DEALER WHERE THE CONTACT WAS INFORMED THAT THE FAILURE COULD NOT BE REPAIRED. THE CURRENT AND THE FAILURE MILEAGES WERE 1,200. ..UPDATED 04/16/12 *BF UPDATED 05/07/12
Complaints are unverified consumer reports submitted to NHTSA. A high complaint count may reflect vehicle popularity, not defect severity. Data sourced from NHTSA public records.
Data synced from NHTSA on Apr 25, 2026