P0300 and P0128
 

Hey Guys,
I have a 2006 H3 Hummer and here recently I have noticed that my lights go dim and heater/AC runs low when stopping. After I stop, they pick back up to normal. I also noticed that it runs rough and idols rough. I took it to AutoZone and the codes are P0300 (Multiple Misfire) and P0128 (Thermostat). I just changed the spark plugs and wires two months ago- did not help. Today I replaced the air filter and took the battery terminal off to clean (It was really corroded). I drove it around a little and the Check engine light went off. I am sure the computer just hasn't caught the errors yet.

I also put some fuel injection cleaner in today thinking it might be that.


Anything else I might need to do?

I have noticed about two times that when trying to start it would die and I would have to pump the gas pedal two or three times and it would fire right up.

the thermostat needs replacing and you also need to clean the maf & trottle body need to take the entire intake system apart to clean these make sure to take tb off clean both sides of it and then reinstall. You also may want to check your spark plugs and check your coil packs and also spray inside of those with a WD 40 or silicone based spray and let them dry out or blow out with air.
Chris

The spark plugs are 41-103 acdelco I would suggest using Chemtool & only on the throttle body and get yourself a dedicated MAF spray you can you get those at Autozone or you can get them online it eBay or Amazon.
Chris

Thanks Chris! Hopefully these will work. I bought the H3 brand new and it sure has been good up until now (well, the melted blower resister and pigtails were a pain to replace). Now that it hit 96,000 miles, time to give it a little TLC.

I notice the same issue with the lights dimming and AC/heater running lower while braking, but I don't have any codes or a check engine light, and I'm not idling rough or having trouble starting. Are we likely experiencing the same issue?

I was having the same problem with mine, I bought it less than 6000 miles ago. I took the whole intake assembly and throttle body apart, cleaned everything (MAKE SURE YOU USE THE SPECIAL MAF CLEANER ON THE MAF SENSOR!). Also threw a new set of Acdelco iridium spk plugs and K&N air filter in while I was at it.

After all that I put everything back together, started the truck and immediately noticed a greatly improved idle, and the stalling/rpm fluctuating at stops was completely gone! She's purring like a kitten now! Definitely the best two hours of TLC I've done on the H3 :D

Did all this at around 90,000 miles, I bought the truck with 84,000 miles in Sep 2012 for 12k! Think I got a really good deal.

Also I forgot to mention that I was getting the P0128 Thermostat replace code as well, and after I cleaned everything it went away and hasn't come back! That was 6 weeks ago. The engine temps are much more stable (staying at 1/2 all the time), where as before they would fluctuate between 1/4 and 1/2 of the temp. guage.

Glad I don't have to replace the thermostat yet, because from what I've read it's a pain in the arse...

After cleaning the MAF sensor, taking apart the throttle body/cleaning, and putting new battery terminals on, I noticed a big difference. Sounds better and no dimming lights and slow heater. However, noticed that this morning, that the check engine light had come on, so I am going see what code is tripping now.. Its running great, so i do not know what it could be... I would think the thermostat would be good because the heat works well....

Couldn't be any worse than having to change the blower resister and pigtails...:cool: Not to much room to work with while repairing it and its an awkward position to have to deal with too...