2021 Chevrolet Silverado 3500: check engine light

Filed Feb 20, 2026 · Fuel system · NY

Service engine light kept coming on the dash, and the code came back to a faulty DEF heater. My truck had a reduced power countdown on the dash indicating the truck was going go to into limp mode after x amount of miles. On warmer days the code would go away and there would be no reduced power. The vehicle was diagnosed at a GM dealership and confirmed the DEF heater was bad, but was notified that there is a bulletin with GM for this issue occurring in many other diesel trucks. My safety was put at risk due to the rapidly changing reduced speed milage, at any point it could drop from 100miles, to 10 miles until reduced speed. This could cause an instant car accident while driving if the truck were to randomly slow down to a speed much slower than the speed limit. IE- driving on the north way (65 speed limit) and having the speed drop to 5mph unexpectedly when you just had over 100 miles to reduced speed.

Filed Feb 8, 2026 · Electrical, Fuel system · OH

My 2021 chevy 3500hd diesel had the engine light come on and the service emissions system popped up in the info screen. It said in so many miles speed would be limited. I took it to the dealer and they said the def tank would need replaced because the tank wiring connector overheated and would cost me over $2k.

Filed Oct 18, 2025 · Brakes, Engine · TX

I was driving down the highway at speed limit when the dash lights came on and the truck started jerking went to a mechanic and he stated it was a fuel ejector after getting it replaced the issue still occurs often check engine light comes on and off and this the only transportation I have for work

Filed Oct 6, 2025 · Transmission · 146,000 miles · GA

The contact owns a 2021 Chevrolet Silverado 3500. The contact stated that while driving approximately 65 MPH, the vehicle unexpectedly went into Low Power Mode, with the check engine and low power mode warning lights illuminated. The contact was able to restart the vehicle. The vehicle was taken to an independent mechanic, where DTC: P2706 and P2732 were retrieved, and the contact was informed that the valve body and certain components of the transmission required reprogramming. The vehicle was not repaired. The contact later received notification of the federal safety agency Campaign Number: 24V797000 (Power Train). The dealer was contacted but the vehicle was not diagnosed or repaired by the dealer. The manufacturer was not made aware of the failure. The approximate failure mileage was 146,000.

Filed Dec 26, 2024 · Fuel system · OH

Injector #4 connector harness issue- Known issue on the 6.6L duramax. Driving with my children for Christmas pickup and power reduction occurred while passing another car on the road. Causing us to hit the breaks as the truck wouldn’t allow us to pass timely. Known harness issue by GM and instead of covering I had to pay to have a new connector spliced in. Multiple warning lights. Check engine, Emissions warning, Reduced power, Traction control, parking brake

Filed Jul 7, 2022 · Fuel system · KS

Check engine light came on followed almost immediately with an Onstar warning to service the engine and transmission within 7 days. Took truck to dealer. They diagnosed problem was fuel system contamination. Hole was found on the inner mesh liner of the fuel filter which allowed water and a sludge like material to get into the fuel system.