GM SB 08-06-04-045 Code P1133

T.w. Anderson · August 12, 2019

2008 Chevrolet Avalanche LTZ 6.0L AFM was bone stock but in excellent condition when I bought it used 600 miles from home with 171,000 miles on it. Let me pre-empt this by saying my son used to haul gasoline. So I know the places to avoid, and the ones safe for fresh, properly blended fuels. I don't buy cheap. And as a matter of fact this first leg of the trip I was treating that 6.0L with a tank full of 91 and a can of SeaFoam just in case there was any storage crud or water in the tank! 100 miles down the road it threw the P1133 code. So I got it home and first thing I do is go to Chevy dealer and buy an OEM gas cap. Always helped stop false codes on other GM vehicles. Nope. So I changed out that banks sensor with a Denso OEM replacement and cleared the code with my OBDII reader. Thirty miles down the road it threw P1133 again. I figured I got a defective new sensor so I swapped left to right on my exhaust and cleared the code again. 20 miles down the road I got P1133 and P1153. Hmmm. I figure it must be a defective new sensor and my fooling with the other side killed that one too. Just my luck. So I returned the new sensor to AutoZone and got a courtesy replacement. Purchased a second one and installed two new OEM Denso sensors and once again cleared the codes. 20 miles down the road I get CEL and read P1133 and P1153 again.

Time to take it to the local Chevy Dealer. I wanted them to look it over anyway and perform my first oil change.

Chevy dealer "flashed" the computer and told me it should be fixed. 10 miles down the road. Nope. P1133. So I returned it to the dealership. $90 diagnostic charge later it is diagnosed as two exhaust manifold bolts "probably broken". $1,600 repair. Not doing that to a $14,000 used truck so I took it to an independent shop that my favorite hot rod exhaust shop recommended. $500 fix for 3 bolts. In the meantime I had the exhaust shop check the cats. The exhaust sound to me sounded like the cats or the muffler were blocking exhaust. Nope checked okay. Cleared the code once more. 20 miles down the road P1133.

Took the truck to the independent shop in our city widely praised for resolving electrical problems. They checked the wiring harnesses and not finding any faults insisted on replacing all four sensors. I gave them instructions and permission to drive the truck until they had at least 100 miles on it. They only got 20 miles on it before the code P1133 re-appeared. They checked and cleaned the MAF, checked but did not replace the plugs but they did replace the plug wires and still got the same P1133 code. They finally put a heat sensor gun on the cats and found they were both defective. Wanted $1,900 to replace those in addition to the $1,400 already totaled up. Nope. Got my truck back and checked with Chevy dealer. They wanted $1,900 for two cats as well. So I know where the independent got his pricing. Took it to the hot rod muffler shop (ASE certified exhaust specialists with header, cat, exhaust and muffler distribution rights for the highest quality brands). They charge $260 per cat for Magnaflow replacements that are supposedly compatible with all domestic exhaust systems. Price was so good I replaced my 10 year old OEM muffler with a healthy sounding Magnaflow as well. But on the drive home I once again got the P1133 code.

7/9/19 The truck is back at the Chevy dealership for a RH taillight signal/brake bulb short. I asked them to check whether there was any newer fixes for the P1133 code. First thing they said was they can't determine a problem if it has a non-OEM exhaust. But they could fix that for $1,900, including a muffler. When I balked at that response they said that one of my two new cats wasn't working anyway. I told them I wasn't going to have them replace my exhaust as a possible fix. If they don't know what the fix is would they please research it.

So is there a fix for that dang P1133 code since GM SB 08-06-04-045 and 045a evidently does not fix the low tolerance to voltage differences????