O2 Sensor

AZ-Z71 · December 9, 2003

Ok so I just got the call from the garage. I had to have the exhaust bolt machined out of the head. No big suprise and figured I would have to have that done. So I guess the truck is ready. They reinstalled the head and exhaust manafold. The code they pulled out of it was for low efficiency of the cat. They went ahead and cleared the code. Currently the SES light is off which I expected for clearing out the code. They were not sure if fixing the broken exhaust manafold bolt will have fixed the problem and warned that the light may come back on, although fixing the bolt is a good start. I'll have to find out more once I pick it up if there is a way to test it if the SES is cleared and if they know for sure if it is the cat. Maybe with a tech two? They also do emissions there so maybe they tested it that way. I'll have to find more out.

I guess I can drive it for a few miles, a couple of starts or what every it takes to let the PCM run the checks and see what code it kicks out then.

If it is the cat I was told it would run me about $750 for parts and labor.

Does anyone know, is the cat a bolt on or is it welded in there? $750 seems a bit much for that. I may have to shop around unless that is fairly close to the going price.

JayMan · December 9, 2003

Well, if the MIL is staying off, I would put on highway miles to clear things out. At least 50-100 Interstate miles. So it sounds like you finally hooked up with a good shop? That's a lot harder than whatever work you need done!

All the popular OTC scantools, such as the Genisys and Pathfinder, come equipped with or can be upgraded to GM certified software, including bidirectional (SPS Reprograming).

The OTC Tech2 is the scantool used at GM dealers, and the Helm shop manual uses the Tech2 menu and screen for examples. I think the Autotap will also work here, though not sure. If in doubt, use an OTC Tech2, Genisys, or Pathfinder with the most current software upgrade.

That code will clear itself if certain conditions are met. I believe I mentioned them in your other post. You can also use the appropriate scantool to "freeze frame" or do "live data" and compare the readings of each O2 bank.

If the O2 sensors "agree" with each other most likely the O2 sensor(s) are bad and if enough damage the cat is also bad.

On my truck, the cats are welded on. Good luck with this!

AZ-Z71 · December 10, 2003

Ok got the truck back. I think I found a winner when it comes to shops. They seem pretty knowledgable. Turn out they ran some test and it is the cat. They turned the light off but of course it came back on. So after Christmas it looks like I'll be investing in one of these.

The shop owner has a lowered chevy, 3500, the tech that work on the truck has the 2500 4x4, the parts order and shop forman has an older chevy 1500, and another guy there has the Avalanche. So I think I'm at the right place. (And all their vehicles are nice looking, hahaha)

Anyway, they make their own custom exhaust and I think when I have the cat done, I'm going to have them build me an exhaust as well. The owners truck has a true dual exhaust setup with flow master 40's and no cab resononance (sp?). Some of the other guys are not as loud so all I need to do is listen to the one I want and tell him to make it.

So the truck runs a lot quieter now and something strange has happened, see my new thread on CSK.

JayMan · December 10, 2003

First of all, it DOES sound like you found a good shop.

Those are RARE, like hen's teeth. I've known guys who have traveled 1,200 miles out of their way to find a good machine shop or good engine builder.

Think about it: you can either put up with the aggrevation of dealing with a bunch of a**holes and complete f***ups, or you can get it done right the FIRST time.

Sadly, it looks like the exhaust leak has either melted or poisened the catalytic converter. I would recommend putting in new O2 sensors while you're at it, as they probably got contaminated too.

Geez, I would really like to put in a TRUE dual exhaust but nobody within 500 miles of me knows how to do it properly. I don't see what you gain by putting on a "cat back" as the exhaust gasses have already entered the single pipe. The GM system is actually a true dual system until it enters that single exhaust pipe: each bank of the motor has its own cat and O2 sensor system, and they operate independently.

Not only does your shop crew drive a nice fleet of Chevy / GMC trucks, they know what the hell they're doing! I'm envious and may have to justify a long road trip just to get a "true" dual exhaust.

Let me know how the dual exhaust works out.

ness5575 · December 10, 2003

$750 just to replace the cat converter? it doenst seem to be too labor intensive to change that out - is the part that expensive?

i do not have the manual in front of me, but arent those warrantied for a lot longer than the standard 3/36?

AZ-Z71 · December 10, 2003

Don't know what the warranty is but I'm at 97,000, so if it is 100,000 then I guess it would be free. Probably like Jayman said, got fried due to the leak.

Checked the local dealer for the part and it is looking like $550 for the cat. Comes as a complete system, bolt on deal, from the manafold to where they come together so you are so I guess you are actually getting both cats (each side). Figure an hour or two to get the bolts off and on and test it, ($80 per hour), I guess $750 is in the ball park. These guys are honest. Told me about $700 before the machine shop and tax on the head and ended up being less than anticipated. So I'm sure it may end up being less than the $750.

On the true duals, that is what the owner told me, set up almost like true duals anyway, he would remove the pipe from behind the cats to where they come together. Then weld in two seperate pieces from the cats to the back.

I was thinking those two cats on each side was some sort of pre-cat and then they went into a single cat then on to the muffler. Made sense when trying to figure out the O2 sensors and how it can pin point to what bank was malfunctioning.

He said to get the true duals, maybe somewhere between $400-$500 complete...

JayMan · December 10, 2003

Yeah, the machine shop is right: the system is almost a "true" dual exhaust from the factory. There are only 2 cat's, one for each bank of the V8, since the PCM treats each bank separate.

Only after the downstream O2 sensors does each bank enter a Y-pipe into the single pipe to the muffler. So the machine shop only has to chop off the Y-pipe and fab a true dual exhaust.

The trick is finding somebody who doesn't hack your truck to pieces or leave you with one hell of a job, like the characters around here do. I wouldn't trust my local shops to change a rusted-out muffler without setting the car on fire!

Yeah, I just got back from the walk out to my garage and checked out how my cat's are hooked up. It is a one piece deal from the exhaust manifold flange to the cat, and then another flange to the Y-pipe.

I called my local dealer and he quoted a price VERY close to what your's was for the new cat. Unless the aftermarket already carries something like that (Check NAPA, Pep Boys, Autozone, etc), you have to use the OEM part.

FWIW the local dealer parts dude also mentioned the longer warranty on the emissions stuff. Then he cautioned that if they can prove the failure was due to lack of service/abuse and NOT a factory defect, you end up paying for it anyway! He specifically mentioned exhaust leaks betweent the exhaust manifold and the downstream O2 sensor. Yeesh, what a hard a**!

Due to the extreme cold temps here, lot of folks need a boost or offer a boost. That can fry the alternator or PCM. So the local dealer is quite good at denying PCM claims in winter!