May 9, 2026Electrical systemEngineFuel system
GM Duramax L5P diesel engine electrical connector for #4 fuel injector. This failure caused the Diesel exhaust brake, which controls downhill speed, to disengage, extreme shaking of the vehicle, emissions system warning and speed limiting. This occurred while descending a steep grade while towing a 34 feet long, 10,000 pound trailer. This is a known issue with this diesel engine and documented in GM Technical Service Bulletin 23-NA-027. Inspection and repair at a GM dealership confirmed a known issue with the #4 injector pigtail connector caused by improper wire routing and interference wit the Sound Shield and Valve Cover Heat Shield This was a sudden failure of the #4 pigtail connector with no advance warning. In addition to violent shaking of the vehicle, multiple warnings on the DIC indicating that the Diesel Brake was disengaged, the emission system had an issue, and speed would be limited.
NHTSA ODI 11736800
Nov 7, 2023EngineFuel system
Metal in the fuel filter and throughout the fuel system, 38 codes on the computer just in 2 weeks after a full service again at the dealer. All service has been preformed at A GMC Dealer since truck was serviced. 1. P026D - Fuel injection Quantity “A” Higher then expected 2. P06CC - cylinder 8 incorrect 3. P133F - cylinder 8 glow plug offset exceeding learning limits None stop this is happening since [XXX] INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)
NHTSA ODI 11553906
Nov 2, 2023EngineFuel system
Constant issues with glow plug failures, fuel rail failure, fuel pressure failure. Truck has been in the Gmc service regarding these issues constantly for the last year with a total of five repairs and replacement of glow plugs with releaning learning new plugs and now the 6th return to the shop they’re tearing down the fuel system. Malfunction and engine light consistently come on with the same occurring problems generating from the fuel system and glow plugs. Fuel mileage is absolutely terrible and lose of power hazardous to safety!!! Gmc has issued an extended warranty for 15 years and 150,000 miles, but cant and hasn’t found a repair for vehicle and just replaces the glow plugs just so they can fail again and again!!! They need to replace everything that needs to be done and if no fix they need LEMON Law The vehicle. This is ridiculous going back to the shop every two weeks I have my truck in the shop for a month to get it back, to put it back in the shop two weeks later, to have it back in the shop for a month. Since this start 17months ago I’ve only been able to put less then 7000 miles on the vehicle because GMC constantly has the truck! The is ridiculous when you’re paying $800 a month for your payment and insurance on your vehicle that you can’t drive because the manufacturer is constantly having to repair and replace the same thing over and over again
NHTSA ODI 11553304
Apr 15, 2022EngineFuel system
Faulty pigtail connector for fule injectors. Cause The vehicle to shut down even while going down the highway possibly causing injury by immediate deceleration wich could cause an accident. For me on this vehicle I’ve had this happen three times and it has cost me anywhere from $800 to 1000 per injector especially if damage is done to one of the fuel injectors.
NHTSA ODI 11460968
Jul 17, 2018Fuel system
MY HUSBAND WAS DRIVING OUR BRAND NEW DENALI WHICH HAS ONLY 3500 MILES ON IT. THE ENGINE COMPLETELY SHUT DOWN CROSSING A HIGHWAY WITH 55 MILES PER HOUR POSTING AND MY DAUGTHER OF 8 YEARS OLD WAS IN THE BACK SEAT. THE ENGINE AS I SAID COMPLETELY SHUT DOWN WITH NO INDICATOR LIGHTS OR WARNING AND MY HUSBAND WAS UNABLE TO STEER THE VEHICLE. IT STOPPED OFF THE SIDE OF THE ROAD BY MIRACLE AND ONSTAR WAS CALLED AND THE VEHICLE WAS TOWED TO THE CLOSEST GMAC DEALERSHIP. APPARENTLY THE FUEL INJECTOR PUMP WAS DEFECTIVE FROM THE FACTORY. THEN IT ALSO BLEW SHRAPNEL THROUGH THE WHOLE FUEL INJECTION SYSTEM AND DESTROYING AND ALL THE FUEL LINES AND PARTS TO IT. I AM VERY CONCERNED AS MY FAMILY WAS IN THE CAR AND THIS COULD HAVE CERTAINLY BEEN A HUGE TRAGEDY. I DON'T FEEL SAFE WITH THIS CAR AND I WANT A FULL REFUND FOR MY AUTOMOBILE.
NHTSA ODI 11112033