After the first AOS failure the CEL was coming on and pointing to an O2 sensor, and eventually I caught the sensor in the act, so to speak and replaced both the bad one and its neighbor on the other bank.
After the 2nd AOS failure all was well.
Now after just having the 3rd AOS fail and replaced, today the CEL came on. DTCs: P0134 and P1128.
CEL came on with no drama from the engine. Driving along and the light wasn't on then it was.
P0134 - Oxygen Sensor Ahead of TWC, Bank 1 – Interruption of Signal
Possible causes:
-- Open circuit in signal wire or ground wire
-- Oxygen sensor heating not functioning
-- Output stage in DME control module faulty
-- Internal resistance too high
Probably the last possible cause because the failure appears to be intermittent.
I used my Actron code reader to run some O2 sensor tests and all that were supported came back with passing results. 'course I shut off the engine before running the tests -- the code reader was in the other car -- and I know shutting off the engine from my previous time trouble shooting O2 sensor problems often (make that almost always) "fixes" the sensor, at least for a while. That was why after the first AOS failure it was so hard to catch the bad sensor in the act.
I'm going to have a tech check the sensor wiring. The car was just the shop and while I doubt it maybe a sensor connector got compromised. Also, not too many months ago the exhaust manifolds were replaced and that P0134 could be from an exhaust leak, which is a long shot as I don't hear anything.
As for the P1128 error code:
– Incorrect signal from MAF sensor
– Intake air system leaking
– Fuel pressure too low
– Volume supply of fuel pump too low
– Fuel injectors fouled
– Exhaust system leaking
Could be the MAF -- I can't tell you how many miles this MAF has lasted -- but the engine is running OK.
Some time back the oil filler tube cap was found leaking so I'll be sure to check that out. Kind of funny what becomes a "wear" item after the miles start to add up.
Fuel pump is relatively new. I replaced it at either 200K or 220K miles. 'course, they can go bad at any time but it doesn't feel like a fuel pump problem.
Plenty of fuel in the tank. Just filled up (paying ... now get this: $3.819/gallon! Yeah, baby!)
The engine doesn't really act like fuel injectors are fouled.
Exhaust system leak? Tthe exhaust manifolds were replaced not too many months ago and a leak is always a possibility, but I do not hear anything that remotely sounds like an exhaust leak.
I'm thinking MAF or a leaking oil filler tube cap. (Missing this before had me replace a perfectly good MAF.) A leaking oil filler tube is also a possibility. At some place IIRC there is a rubber bellows that can crack.
More when I know more.