Hello all,
I have a 2003 H2 with 180k miles, a week ago or so when I was coming back from a trip the check engine light came on and would flash when accelerating above 55. I babied it home and took it to Autozone, scanned and said O2 sensors. So I replaced those, same issue. Took it to the shop, they had it 12 hours and charged me an arm and a leg, couldn't fix the issue. Said it was the MAF and misfire on 2 and 7. They cleaned it, same problem. So I babied it home. Changed plugs, wires, coils, MAF, O2 sensors, air filter. Runs great in park, will rev fine and idles smooth. After 2-3 minutes the check engine light will flash. If I put it in drive or reverse it will barely move and almost stall. Any suggestions would be appreciated. Thanks

 

sound like you need to check if your catalytic converters are plugged up.

 

Hard to say for sure... could be any number of things. While often effective, the parts cannon is generally not a great method of troubleshooting as you often also replace a bunch of things that were fine. Need to look at live data like fuel trims, O2 sensor voltages, etc. Another possibility could be fuel pressure caused by pressure regulator or fuel pump or since yours is a 2003 you do have an external fuel filter attached to the frame near the fuel tank which could have become clogged.

 

On mine, the air filter was really dirty. Lol, I had bought it the month before the light came on. WTH.

 

Exact symptoms and MISdiagnosis I got from 2 GM dealers before the third agreed with me that it was plugged cats.

Lots of utterly incompetent GM mechanics out there. Look at my and others threads on plugged cats. Ask you dealer for a refund, due to incompetency. Go elsewhere. Check pre and post cat pressures and temperatures. Usually the passenger cat is the culprit.

VERY common problem that throws nonsense codes, and usually lots of them.

Get ready to spend a lot more $$

 

P0300 is normally due to carbon buildup on the valves. Induction cleaning eliminates the carbon.