PO420 & P0430 Engine code

[Waldo]

Check engine light has been popping up on my dash off and on for about 2 months, gone to the dealer and they just clear the code and tell me it's fine, I drive away and it comes back anywhere from a half hour to a day later. Biggest issue is the dealership is telling me that they're taking it for a test drive and not getting any codes, yet I can pick up my truck at the end of the day and the mileage hasn't changed more than 1-2km's. I also had the dealer do an "Injector flush" with my 60,000km maintenance and not long after all of this started to happen.



P0420- Bank 1 Emissions system inefficiency

P0430-Bank 2 Emissions System inefficiency



2009 H3T Alpha 67,000kms

Symptoms: Rough idle, surging at intersections, bogging upon heavy acceleration, heavy fuel smell on start-up for about 3-5 minutes, black or brown smoke from tailpipe, HORRIBLE fuel economy (getting fuel every week to every 2-3 weeks)



Probable causes that I've dug up so far: Bad O2 Sensors, Plugged Catalytic Converter, bad M.A.F, bad plugs, or an exhaust leak



Self diagnosis (Since the dealer just looks at a flowchart on a computer and gives it back without trying to diagnose it)

- Searched for an exhaust leak: started engine, let it idle and crawled underneath running my hands along exhaust feeling for air moving at any connections or along exhaust

- Checked plugs: pulled all 8, while they could use a change they weren't fouled or overly carbon coated.

- Cleaned M.A.F: Pulled mass airflow sensor, and cleaned with sensor cleaner

- Ran off-the-shelf injector cleaner and a few full tanks of premium through the truck



Problem is still on-going. Have used my scanner to check voltage on O2 sensors, I have one downstream O2 sensor not staying inside the parameters I found online. While the last two weeks I have been beating the snot out of the truck trying to clean out the cat's if that is what the problem could be. I haven't had smoke out the tailpipe for a while now, although my fuel economy is still sucking out loud, running around 7-8.5MPG vs 15-17mpg last winter.



Wondering if anybody else has had these issues, or could point me in a better direction. I will be calling another dealer tomorrow as well have filed a complaint with GM Canada with my dealership about the lack of any repairs being done.

[johnnyspikesH3]

Take it to another dealer for sure . Hopefully the Mechanics on here can put in their 2 cents .

[whitehumh2]

OK, I would suggest that you redo your exhaust leak test. You need to create some backpressure. Have a second person use a glove or rag and block the exhuast tip, this will make the exhaust search for the easiest way out. NO Leaks= Not the Problem! If you are questioning the CATs as the source of the problem, you can do one of two things, both will work. 1. Unbolt and remove your CATs and go for a drive, if your power is back then your CATs are the cause. 2. Remove the pre-O2 sensors and go for a drive, look for the same results as in #1. Note: both ways are very loud but will prove if the CATs are the source of the problem. I would be suprised if both your CATs are blocked at 60000km, I am more in the direction of the O2s being defective or that you have a wire that has rubbed thru. Check the Driver's side post O2 sensor, if the connector retainer clip is broken the wires can rub on other parts. Check the passenger side as well since this could rub on the front driveshaft. And yes take it to another dealer and tell them to drive it for a day before they say there isno problem!

[Gadgets]

I had a work van years ago that had a plugged up Catalytic Converter. You are describing what that truck did to a tee, it got bad enough that I could pretty much stall the truck out on heavy loads like a steep long hills and things. Replaced it, and all was good. But that was a GM Astro van so was a few years ago now, and not a Hummer. Keep us posted.

[Waldo]

Last night before a friend an I went out to watch the UFC fights, I had him help me out and do the exhaust leak test again. I had him place his hand with a glove and an old rag behind the tailpipe, crawled underneath and started reaching around to find a leak. Still couldn't find a leak, but I could hear a bit of clanging coming from the exhaust system once we started driving around.

-Checked for broken wires couldn't find any, nor did I find any rubbing on any hot surfaces.

-Code has been gone for most of the weak so I won't be wasting my time taking the truck to the dealer tomorrow. But the truck seems to have it's power back, I can't really seem to place why it's been lacking for power and now all of a sudden it's back.



I ran my scanner on it again and these were my findings: the voltage ratings jump from rich to lean

engine running @ 2000rpm

S1B1 (upstream driver's side) 0.100v-0.795v

S2B1 (downstream driver's side) 0.635v-0.705v

S1B2 (upstream Pass. side) 0.100v-0.785v

S2B2 (Downstream Pass. Side) 0.715v-0.745v



From that it's telling me that one of my downstream sensors should be bad. Downstream sensors should only jump a short distance in voltage. I'll try to swap them out and keep you guys posted.

[whitehumh2]

If you are hearing a clanging that is non mettalic and your power comes and goes...it could be a CAT that has broken and sometimes, the parts align and it works and other times it blocks flow. Take a rubber mallet and gently tap on the exhaust. Start at the rear of the exhaust system and work your way forward. You need to check the muffler also, since it could be a baffle that has broken free as well...very possible.

[gram]

I agree with polar bear. It sounds like bank 1 has a piece of the honeycomb in the cat turning sideways from time to time. Only real diag is to remove the y pipe and see what falls out when you shake it. At least youll be able to look inside. I had the same problem with my yukon, 5.3L only the previouse owner mixed the red and green coolant together, causing the rad to block solid in the middle of summer on the highway. The heat was enough to melt the insides of the cats and give me a no power senario after replacing the rad.

[Waldo]

Wow I nearly completely forgot about this, it's been a hectic few months.

My scanner was reading that the downstream O2 sensor driver's side was reading lower voltage than the rest, swapped sides, same issue on the same side. Pulled the Y pipe of (P.I.T.A) couldn't see any damages or anything loose floating around nor could I hear anything loose clanging around.

Reassembled and the problem went away for about 2 months then C.E.L light popped on the dash after a 7hr roadtrip. Got it checked out, swapped the upstream O2 sensors, checked for exhaust leaks, and changed my spark plugs.

Again the issue went away but it's been back now, off and on since I got back from the Alberta chapter's October trail ride. Where I may add, I got a whopping 637km to a full tank of fuel!

Could it be possible that after the trail ride, on my drive home the the truck may have ran lean, leading to that great gas mileage and possibly cooking the cat's?

I have plans to get a full exhaust installed in the next few weeks, the owner of a local exhaust shop is heading to S.E.M.A and lookibg out for who makes either short tube or long tube headers that will bolt into these oddball rigs.