2008 GMC Yukon: sudden loss of power

Filed Apr 29, 2025 · Engine · NY

I purchased a MagnaFlow aftermarket catalytic converter system for my 2008 GMC Yukon SLT 5.3L through Walmart’s online marketplace, sold by a third-party vendor called OurDealsRock. The product was advertised as “50-state legal” and compatible with vehicles registered in New York State. However, shortly after installation, my check engine light turned on, and diagnostic codes P0420 and P0430 (Catalyst System Efficiency Below Threshold) appeared. Initially, I thought this was a minor sensor issue, but over time, the vehicle’s performance gradually deteriorated. I noticed reduced acceleration, poor fuel economy, and eventually significant loss of power. The vehicle began shaking under load, misfiring, and overheating. These symptoms worsened steadily—not immediately—but progressively after continued driving with the aftermarket converter installed. I had the vehicle inspected by a certified mechanic, who confirmed that the MagnaFlow converter was not CARB-compliant, was not approved for use in New York, and that it had been illegally marketed as such. He also informed me that prolonged use of a non-compliant, malfunctioning converter caused excessive backpressure, leading to complete engine failure over time. The diagnosis was confirmed by a second mechanic before I committed to the engine replacement. The product was later removed from Walmart’s site, becoming unavailable for sale in my zip code [XXX] ) shortly after my initial complaint. This shows clear acknowledgment that it should never have been sold to a New York consumer in the first place. But by the time it was taken down, the damage had already been done. Component/system that failed: •MagnaFlow aftermarket catalytic converter system •Ultimately caused failure of the vehicle’s engine block Safety concerns: •My family and I were unknowingly driving with a damaged and failing engine •The vehicle’s degraded performance, overheating, and power loss could have compromised our safety during highway d INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORM

Filed Dec 11, 2017 · Fuel system, Transmission · 115,000 miles · CA

Tl* the contact owns a 2008 gmc yukon. While driving approximately 60 MPH, the vehicle stalled and the traction control and reduced engine power indicators illuminated. The vehicle was taken to an independent mechanic where it was diagnosed that the fuel control module and the body control module were faulty and needed to be replaced. The technician replaced the fuel pump, but the failure recurred. The dealer (allen gwynn chevrolet, glendale, ca, 844‑636‑8480) scheduled an appointment. When the contact arrived for the appointment, the technician stated that there was no recall. The manufacturer was made aware of the failure and stated that nothing could be done. The vehicle was not repaired. The failure mileage was approximately 115,000.

Filed Feb 21, 2017 · Fuel system · 65,000 miles · TX

My vehicle experienced an electrical short in the fuel pump flow control module, causing the engine to stall while I was traveling around 70 MPH on the freeway. I lost engine power, power braking, and power steering. I nearly had an accident when pulling off to the shoulder and braking. I am aware that there was a recall of the part that failed in gm bulletin 14515b. Gm however informed me that my VIN was not covered under the recall. The defect in my fuel pump control module has been confirmed by my gmc authorized service center. I am looking for reimbursement of the $550 dollars I paid to sewell service to replace this component as it surely should have been covered in the recall.

Filed Feb 8, 2017 · Driver assistance, Electrical · 120,000 miles · OK

The car flashes reduced engine power, stabilitrack off and the car can barely go 30 MPH. The engine runs very rough when it is doing this also. My code scanner displays code 641 which is open 5volt reference on bank 1. It does this more when the weather outside is warmer or the car has been sitting still while running. On more than one occasion it has happened while pulling out into traffic causing near misses and other times while driving down the highway. Just yesterday it did it 20 times in a four mile stretch. This car is no longer safe to drive.

Filed Apr 1, 2015 · Driver assistance, Electrical · 108,730 miles · AR

While traveling on the interstate at speed (70) the stabilitrac light came on and reduced engine power message displayed. The RPM's went over 4k, then the yukon slowed in traffic and I had to pull to the side before being run over. The accelerator was unresponsive at that time. I turned off the engine, waited about 5 minutes and then resumed driving using '3' to engage transmission instead of 'd' the check engine light remained on, but I made it to my destination 2 hours away.

Filed Apr 7, 2014 · Acceleration · 64,000 miles · NC

When traveling on a very busy interstate, I backed off the gas and went to accelerate when my vehicle went to reduced engine power. Thankfully, the car made it to the next exit which had a gm dealer. They replaced the acceleration pedal position sensor. The car was purchased new in march 2008. This issue happened the first time in march 2012. 2 years later in march 2014, this issue happened again. The same part was replaced. We contacted chevrolet and filed a formal complaint. We were told they would probably not do anything, it's scary that a gas pedal has been replaced I a vehicle twice in 6 years.

Filed Aug 31, 2010 · Electrical, Fuel system · 23,000 miles · CA

Purchased a used 2008 gmc yukon jan. 23, 2010 and approximately 4 months later the first issue occurred with the car not starting in my driveway. I thought it was user error. A few months later coming out of the grocery store went to enter my vehicle and no start, went under the hood and moved the battery cable and it started. Later that night I tried to tighten the battery cable, but it wasn't loose. Approximately 1 month later while driving, the dash flickered and "stability traction" light illuminated with slight loss of power. Got to destination exited vehicle and upon return vehicle would not start until I once again moved battery cable around. The last incident which occurred on august 30, 2010 while driving approx. 15 MPH through a residential neighborhood, engine just cut off. Wrestled car to side, put in park and restarted. This was the scariest incident because someone could have rear ended me. I took vehicle to shop gmc dealer and they found nothing wrong. 23,000 miles on vehicle now. Purchased with 17,500.

Filed Jun 4, 2009 · Acceleration · 27,279 miles · FL

Reduced engine power intermittently and without warning vehicle will not go above 35 MPH. Has occurred five times with a different "fix" each time. One of the times it occurred my teenage son was driving on the interstate and had to pull over. Another time it happened my daughter was driving the vehicle and fishtailed taking a corner and had continued deceleration going up the bridge. Major safety issue!