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Gary, GMC Technician
Category: GM
Satisfied Customers: 16759
Experience:  15 years gm master tech/15 years ASE master tech
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I have a Hummer H2 2008, and have been struggling with a

Customer Question

I have a Hummer H2 2008, and have been struggling with a P0430 for quite some time. Living in spain, and the only 2 hummer mechanics around here have pretty much given up. The fault seems to come when stopping for a red light, and the engine is at idle... looking at live data the wrong reading from sensor 2 appear to be just momentarily. The amount of work has been excessive, and I am not making this up.
New head gasket.
New catalytic converter.
New o2 sensors.
New wiring harness.
New spark plugs and wires.
New air mass sensor.
Changed ignition coils from one side to the other.
New headers and gaskets.
Hope you have some kind of idea, since my patience is about to run out, and feel I have thrown enough money after this project. Hope you can help me out!
Submitted: 1 year ago.
Category: GM
Expert:  Gary replied 1 year ago.

I am sorry your having this problem

which converter was replaced ?

how does it run when driving on the road other than the code P0430 keep being set ?

Customer: replied 1 year ago.
Both Catalytic converters were replaced. The car runs very well, it is just that code that comes up pretty much every time I go for even a short drive, and always pops up when at idle.
The rpm is not always completely stable when at idle, but some mechanic told me that is normal. I also replaced the alternator and put in a powerful Odyssey PC1220 battery, because the mechanic thought the problem was laying there.
Expert:  Gary replied 1 year ago.

were they GM converters ?

and both O2 sensors replaced for that bank ?

and i am assuming the wiring to those O2 sensors is good ?

Customer: replied 1 year ago.
The converters are GM, All 4 O2 sensors replaced also original. Since the engine wiring harness is brand new, I assume that also includes the part that goes all the way to the O2 sensors.
Expert:  Gary replied 1 year ago.

when the code is cleared how long before it will reset ?

Customer: replied 1 year ago.
On average, once in every 20 times or so I idle for 2 minutes, it comes on
Expert:  Gary replied 1 year ago.


at this point with new O2 sensors and GM cat converter the only things left to cause this issue is to be sure there are NO vacuum leaks and the injectors are pressure cleaned

if the code still comes back then the only thing left is to update the programming in the computer as there has been a few updates to correct some O2 sensors reading wrong and the programming in the computer updated should correct any of those issues

if it STILL does this after updated programming then there is nothing left but a bad computer

Customer: replied 1 year ago.
Ok, will give it a go, and come back to you with the outcome of your instructions.
Might be a while since I will instruct my mechanic to do it.
Thanks so far!
Expert:  Gary replied 1 year ago.


you can always get me back through this post for FREE anytime with any follow up with this question anytime even after you rate us here at Justanswer !