P0305 cel code came on and took it to a mechanic. They diagnosed the issue and did a compression test which produced results of cylinder 5 having 70 psi and the other cylinders were normal. Determine that the valves seats are bad and it is a common issue on the Hummer H3. Total cost for repairs was projected to be $9,000 for all parts and labor.

- Houston, TX, USA

P0300 code. Engine misfire. The Hummer forums I've researched say it's a common problem in these cars, manufactured before March 31, 2006. It seems the engine heads do not have properly hardened valve seats. Again, I'm finding this is a common problem and GM is fully aware of it.

- Henderson, NV, USA

I have owned this car for 10 years. Its always giving me problems. Especially the electrical and engine. I've gotten 3 notices in the mail for recalls and GM has ignored my request. At this time I am holding them responsible because my Hummer H3 is always in and out of the shop and dont feel like ive gotten the value I deserve on my purchase. Please give me call at [xxx]. imy name is [xxx]. even though there are no more Hummer dealerships and no one specializes in the care of this vehicle, I have taken complete care inside and outside of my investment and hope to get some type of leeway in this matter. Thank you. Information redacted pursuant to the Freedom Of Information Act (FOIA), 5 U.S.C. 552(B)(6).

- Los Angeles, CA, USA

The contact owns a 2006 Hummer H3. The contact stated that the vehicle failed to start intermittently. All the warning indicators illuminated on the instrument panel. The vehicle was taken to Cadillac of naperville (located at 1507 ogden ave, naperville, il 60540, (630) 355-2700) where diagnostic testing was completed, but a failure code could not be found. The vehicle was not repaired. The manufacturer was notified and did not assist. The approximate failure mileage was 100,000. Consumer stated anti-theft device was malfunctioning.

- Orland Park, IL, USA

My truck is burning excessive oil between oil changes

- Newnan, GA, USA

I purchased the vehicle with approximately 900 miles on it. At approximately 40,000 miles, I had to have the cylinder head replaced. I was told at the dealership that the head contained a known defect. At 80,000 miles, the cylinder head had to be replaced again, as the dealership installed a second defective head when they performed the first repair. At 127,000 miles, the cylinder head has failed again, as apparently the dealership installed a defective head when they performed the second replacement.

- Eagle River, AK, USA

Truck will not start for no apparent reason. Key turns, sounds like it will start but does not. This has happened on several occasions and seems to be an ongoing problem for other Hummer owners too. I just had it towed once again to the mechanics shop. This is the 5th time within one year. Unable to leave my house during an emergency, child related.

- Panama City, FL, USA

1) 1.5 years ago we started getting "misfire on cylinder 5" code and now it is multiple misfires. 2) my fancy rims are peeling

- Gray, ME, USA

The contact owns a 2006 Hummer H3. While driving approximately 60 mph, the vehicle shut down, locked up, and did not restart. The check engine indicator illuminated. The vehicle restarted later and was taken to the dealer who was unable to diagnose or duplicate the failure. The vehicle was taken to another dealer where the following codes were run for the check engine warning: C0240, P0106, P0601. The manufacturer was not made aware of the failure. The failure mileage was 130,000.

- Popeka, KS, USA

When I start vehicle smoke blows out the exhaust for 30-90 seconds then it is gone. Sitting still and only does it when it starts up. Googled this and others have had this issue. Head gasket leaking into valves. This is a headache for tons of Hummer owners, so why haven't they issued a recall? started last year, possibly in 2015 and I've just kept an eye on the oil and keep refilling as needed.

- Ball Ground, GA, USA

The contact owns a 2006 Hummer H3. While driving approximately 70 mph, the vehicle shook violently as it approached a stop. While idling, the vehicle operated normally. An independent mechanic diagnosed that the vehicle needed a new cylinder head and sensors. The vehicle was not repaired. The manufacturer was notified of the failure. The approximate failure mileage was 32,000. Updated 07/12/17

- Brooklyn, WI, USA

The contact owns a 2006 Hummer H3. While driving 70 mph, the vehicle independently decelerated to 30 mph. The stability tracking system, check engine, and a third indicator all illuminated. The failure recurred multiple times. The vehicle was taken to a dealer where it was diagnosed that the wires over the engine failed and needed to be replaced. The vehicle was not repaired. The manufacturer was not made aware of the issue. The vehicle was included in NHTSA campaign number: 15V421000 (visibility). The approximate failure mileage was 50,000.

- Warren, NJ, USA

There are many forums about cylinder misfires - especially after the warranty runs out. I looked it up and was shocked to see how many other people have had the same issue and nothing has been done about it. Every Hummer owner I know has paid thousands of dollars to get their problems fixed. Why is there not a recall when so many have the same problem?? the idle is rough. The engine sputters. The light goes on and off constantly.

- Somerville, TN, USA

I purchased a 2006 Hummer H3 with only 100K, after performing a complete service I was made aware the cylinder heads are "defective" the vehicle was driven for 5 monthe then the check engine light came on.. a code scanner indictacted a #2 cylinder misfire replaced spark plug, coil pacack and injector no luck I was informed cylinder head need to be replaced, at what cost does the NHTSA realize that this was a major manufacturing defects, yes GM replaced cylinder heads under warranty but with the same defective heds as to pass on the cost to the consumer as soon as the warranty expire to get their warranty money back., there has been numerous complaints and yet nthsa refuses to inform GM of the "defect" it seams all the ntsha cares about is electrical concerns on vehicles, so who make the determination the a poor designed cylinder head should be the consumers problem. This is where an individual should be held accountable, it took a threat from the NHTSA for GM to issue a recall on the HVAC connector to get resolved., if the NHTSA cannot understand mechanical defects should there be a recall when more than 500 complaints are achieved. So now I am out of pocket $2800 thanks to a administration that has no clue on mechanical issues. You should hire an individual who has mechanical degree to hold car companies responsible for poor mechanical issues so will I receive a response to this issue as we all know GM has informed dealers to give customers excuses as to why they are not liable, my conclusions indicate that the NHTSA only acts on air bags brake switches and electrical issues nothing mechanical.....

- Medford, MA, USA

I have a 2006 Hummer H3 and I've had issues with my ignition switch cutting off while I'm driving down the road. There are times that my car will not start do to this. I've had it tested and it's the ignition switch that I'm taking about. Why is this not being recalled!!!!! someone's life can be taken away for something that keeps happening to these Hummer H3!!!!!

- Thomasville, NC, USA

The contact owns a 2006 Hummer H3. While driving at an unknown speed, the check engine warning indicator illuminated. The vehicle was taken to an independent mechanic who diagnosed that the second cylinder was misfiring and the head gasket and/or cylinder needed to be replaced. The vehicle was not repaired. The manufacturer was notified of the failure. The failure mileage was 70,000. The VIN was unavailable.

- Spring, TX, USA

Approximately at 150,000 miles, while making a delivery at the county disposal facility, while moving slowly and parking at each station, the engine started cutting off and idling very poorly, slightly knocking. I made it home checked the oil' which read low, so I changed the oil, over 5 quarts removed, it only requires 6 qts max, and I replaced it with 5 quarts of full synthetic, with bg cleaners. Initially it started, idled, and ran better but after 30 minutes the engine knocks resumed. The next day I took it to my mechanic, he assessed and diagnosed it, concluding that the engine was bad and needed replacing. I had it that confirmed with another mechanic. Went on the Hummer forum blogs and read many similar complaints about the engine and pistons warping or dying between 75K-150K. Most blaming GM for putting in defective pistons or and undersized engine 3.5L in a heavy all 4 wheel drive vehicle" not sure where to go from here, a used or refurbished engine is $2500-$3500, with installation another$3000-$3500? I'm not sure if it's worth the steep investment"

- Centreville, VA, USA

I have owned my 2006 Hummer H3 for the past 8 years and about 5 months ago it began not wanting to start. Not wanting to start no matter what I do and then starting like nothing was ever wrong after 10 minutes. I'm tired of this happening! my H3 just turned 50K miles and I live in Florida where the weather is warm... this is definitely a safety issue. As a retired Florida police officer I know this to be true... this is a safety issue! you should be able to get inside your vehicle and start it up and leave at your convenience and not when your vehicle decides to... there are so many complaints about this same problem with Hummer H3's I don't understand how there hasn't been a recall on this issue... go to cargurus.com and read some for yourselves... having to worry about my wife being stuck somewhere alone because the vehicle will not start is extremely frustrating... I pray nothing happens to her... this issue needs to be addressed. Really hope to get this problem fixed... thanks in advance...

- Venice, FL, USA

More and more frequently when the ignition key is turned to start the engine, the security system activates and disables the engine and prevents it from starting for 10 minutes. There is no possible override so regardless of where you are (on the freeway, on a rr crossing, at a traffic light, or wherever, the engine will spin but will not crank. You are put in the situation of having to physically push the vehicle out of danger or let it sit until the security system resets to attempt to start it. This has also occurred on my 2005 Chevy colrado pickup which is equipped with an identical drive train as my H3 Hummer. This has happened multiple times, more than 25.

- Statesboro, GA, USA

The contact owns a 2006 Hummer H3. The contact stated that while driving approximately 55 mph, there was a reduction in the engine power as the rpms decreased. The vehicle began to vibrate violently. The vehicle was taken to the dealer on three separate occasions. The mechanic replaced the head gasket and engine coil twice. The manufacturer was notified of the failure. The approximate failure mileage was 30,000.

- Kensington, MD, USA