2015 GMC Yukon: misfire or rough idle

Filed Sep 22, 2026 · Engine · WA

The vehicle developed a recurring cylinder #4 misfire with a flashing check-engine light, rough running, and reduced performance. Diagnostic code P0304 repeatedly returned. Replacing the #4 spark plug temporarily restored normal operation, but the misfire returned after a few hundred miles. The #4 plug was wet/oily, and fresh oil was found pooled in the #4 intake port while the other ports were dry. All eight spark plugs, ignition coils, and plug wires were replaced, along with the #4 fuel injector and both #4 valve-stem seals, but the misfire persisted. A valvetrain/lifter tick later became audible near 3,000 RPM. The failure has now been confirmed as a valvetrain failure that severely damaged/destroyed cylinder #4 and requires complete engine replacement. The vehicle is available for inspection upon request. This defect creates a serious risk of severe misfire, loss of engine performance, or complete engine failure while driving.

Filed May 23, 2026 · Engine, Fuel system · OR

While traveling at highway speeds on Interstate 5 in Oregon, my 2015 GMC Yukon Denali experienced a sudden, catastrophic engine failure with zero advance warning. The vehicle instantly lost almost all propulsion and power while surrounded by high-speed traffic, creating an immediate and severe safety hazard on a major interstate. The engine began making a loud, severe knocking noise, and I was forced to navigate across lanes without adequate power to reach the shoulder. The vehicle was towed and inspected by Point S in Creswell, OR, where diagnostics confirmed a P0300 random/multiple cylinder misfire, with cylinder 4 specifically misfiring. Using a stethoscope and scanner to isolate the failure, technicians confirmed a catastrophic rod knock failure at the bottom end of the engine. The vehicle was then taken to Sam’s Automotive Service, where a complete engine replacement was executed at a total out-of-pocket cost of $16,000. General Motors has a well-documented history of internal engine failures on these 6.2L V8 platforms, yet they have failed to issue a safety recall for vehicles experiencing this sudden, dangerous highway power loss.

Filed May 2, 2025 · Engine · AR

The Yukon was driving normally and just lost power while driving 55mph on the highway. Then I got off the highway to pull over and check it out and the Yukon started shaking while running and in Park. The truck would not drive over 30mph without shaking and what sounds like misfiring.

Filed Sep 16, 2020 · Engine · 165,000 miles · GA

When sitting at a light, or stop sign vehicle acts as if it wants to cut off, check engine light is flashing, when I'm driving vehicle the check engine light stays lit. I did a scan of the vehicle and the code I got was p0303 which is for a cylinder 3 misfire. I have changed out the spark plugs and wires, also the ignition coil. I changed out the fuel injector for cylinder 3 and also the fuel pump actuator. Its still shaking, don't know what the problem is but I hope you guys can come up with what I need to do next. I've had to spend money out of pocket for this because its not under warranty.

Filed Aug 15, 2016 · Electrical, Engine · 3,900 miles · GA

Our 2015 yukon xl denali has been in for repair service for 41 days since purchased new 3/23/15. The car has stalled while in motion with my wife and three daughters in the vehicle twice and been unresponsive to throttle input 3 additional times. The stall occurred once while turning left across traffic and another time while turning right and merging with traffic! The problem is intermittent and gmc has never been able to replicate it. They have given us the shoulder shrug, "I don't know what to tell you, we can't replicate it" line, so here are your keys. No warning indicators, no signs it may happen, and no way to pull up the issue with their diagnostics...huge safety concern and each time they have handed us the keys back after 7 days (their standard allotted time to have a loaner out) without any proactive escalation to find root cause or concern for my family's safety. The last time we took it in, they had it for 8 days and could not replicate the issue. We signed our service paperwork and I escalated to the service manager before leaving. After telling him we would be pursuing buyback, he miraculously had an idea it may be related to a wiring harness issue. This was based off his experience with a sierra pickup (5.3l, not our 6.2l) that had similar behavior. We left the vehicle and, wouldn't you know it, they replaced a wire and "have reasonable confidence" it resolved the issue. Two weeks later, it's back in the shop for key fob not detected (after already driving). Truck is in gear and you cannot move...another huge safety concern. It's a dud. We have also had to have all 8 injectors replaced due to rough idling and the steering gear replaced from faulty manufacturing that creates a clicking while turning the wheel, the car is at the dealer and we will not be taking it back. We are going through the offical buy-back process with gmc.