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Discussion Starter #1
Hi guys, I need some help. My gf has a 08 Mazda 3 2.0 AT. Has 300,000km on it. We had a engine light come on and the codes indicated bank 1 sensor 1 O2 sensor. So we ordered a O2 sensor via ebay special and installed it. The code never went away, and I didn't have the OBD code reader to follow up. I recently went out and bought one after her car backfired through the intake, and it these codes...

p2177 system too lean off idle bank 1
p2187 system too lean off idle bank 1
p2097 post catalyst fuel trim system too rich bank 1
p0131 O2 circuit low voltage bank 1 sensor 1
p0132 O2 circuit high voltage bank 1 sensor 1
p0134 O2 circuit no activity detected bank 1 sensor 1
p2195 O2 sensor signal stuck lean bank 1 sensor 1
p2237 O2 sensor positive current control circuit/open bank 1 sensor 1
p2251 O2 sensor negative current
p2177 pending system too lean off idle bank 1

I cleared everything and went for a quick drive and checked again, these codes showed up as pending;

p2187 system too lean at idle bank 1
p0132 O2 circuit high voltage bank 1 sensor 1
p0134 O2 circuit no activity detected bank 1 sensor 1
p2251 O2 sensor negative current control circuit open bank 1 sensor 1.


To add to everything shes got something up with her exhaust, at first I though it was a cracked header but I couldn't feel any air leaking around the header so I think the resonator has failed - her car sounds like a tank all the time.

I've ordered a new NTK O2 sensor and resonator from RockAuto, but looking to see if there's any other ideas or suggestions.

Thanks.
 

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Discussion Starter #2
Just a follow up. Cleaned her throttle body - it had massive amounts of carbon buildup on the back side - had to scrap off the carbon before traditional cleaner would work. I also dropped the exhaust manifold and found the flex pipe was broken and leaking. I bought just the flex pipe, cut and welded in the new flex pipe and reinstalled everything. Then I installed the new NTK O2 sensor and the car runs like new with no codes.
 

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Anthony14, thanks for the follow-up! Great job on fixing your car.
 

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Discussion Starter #8
Any ideas on why the carbon buildup in the throttle body?
Her car has just over 300000km on it, she bought it used with 100k, and it's probably never seen any sort of fuel system cleaner, or physical cleaning until I did it. With the exhaust leak, she could have been running extra rich, which depending on the amount of time could have contributed to the problem.
 

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A good tune-up would've reduced the carbon buildup, before performance issues manifest.
Tune-ups haven't been tune-ups since the early 1990s. Advances in computerized ignitions systems, direct injection, and the implementation of hydraulic lifters have changed engine maintenance. Tune-ups used to consist of inspection, adjustment, and/or replacement of the spark plugs; inspection and adjustment of the carburetor (go back far enough, and carburetors were oiled weekly); inspection of the spark plug wires and replacement at specified intervals; valve lash adjusted; timing adjusted; and, the points adjusted or replaced along with an inspection of the distributor cap. The air filter should also be inspected based on local conditions and replaced either as needed or at the prescribed service interval.

Instead of the above (which was performed at frequent intervals), none of that is touched until 60K (for the Mazda 3) when the spark plugs are replaced. OE manufacturers recommend the O2 sensors be replaced between 65K miles and 75K miles for efficient operation of the emissions system; otherwise, their performance degrades over time and can lead to the catalytic converter becoming clogged and other issues. A catalytic converter should never have to be replaced if the emissions system is properly maintained. Dodge/Chrysler vehicles were notorious for clogged catalytic converters back in the 90s due to manufacturing defects.

Other than that, there are no adjustments or other part replacements of any kind to the Mazda's ignition system or valve train, hence no tune-up. The build up of carbon in the backside of the throttle body is an entirely different issue. Vehicles were designed with closed loop venting starting in the 70s, whereas before they vented gasses directly to the atmosphere. The PCV system is designed to route those gasses through the combustion process. Those gasses carry carbon particles that clump or build up and are either caught by a filtration system (oil filter) or cling to various areas of the engine's internals. Oil viscosity requirements have changed over the years to meet fuel mileage standards. The manufacturers use tighter tolerances on the pistons and cylinder bores but use lighter tensioned piston rings for less resistance when the engine is in operation. This allows blow-by to occur, which is why newer vehicles use the intake to double as a catch can.

The build-up of carbon on the backside of the throttle body of the OP's vehicle is a natural consequence of modern vehicle engine design, although I am curious if the O2 sensors had ever been replaced. That doesn't mean the lack of their replacement is the cause for the resonator having gone bad, but there is no mention if the resonator was plugged. Most people will lay the blame on a plugged PCV, but that isn't always the issue. I replaced the PCV on my vehicle when it had over 150K miles only as a precaution, and only because I was replacing all of the hoses in the cooling system. The PCV was functioning perfect (and was also the factory specimen); however, the backside of the throttle body was caked with build-up. I follow maintenance guidelines to the letter, so it's not an issue of lack of maintenance on my part. It's a good idea for the DIYer to pull the throttle body and inspect for carbon at every spark plug replacement interval. Throttle body cleaner (NOT carb cleaner) should be used to clean the throttle body and butterfly. Filter inspection and replacement should follow prescribed schedules as well. The PCV on these vehicles is an absolute PITA to remove; however, "an ounce of prevention is worth a pound of cure."
 

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Discussion Starter #10
...although I am curious if the O2 sensors had ever been replaced. That doesn't mean the lack of their replacement is the cause for the resonator having gone bad, but there is no mention if the resonator was plugged."
Your spot on. Her O2's since shes owned them, have never been replaced. I personally have never change O2's until they fail.

Resonator is fine, we had a failure of the flex pipe.

Modern day tune-ups are plugs, air filter and some fuel tank additive. Gone are the days where shops actually remove throttle bodies and hand clean them on a tune-up. I personally usually clean them one once a year or so.

I also did her transmission fluid and filter; I thought I pulled the wrong drain plug the oil was so black. Trans is very happy with the new fluid. Probably original fluid.

I'm happy were were able to get it taken care of.
 
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