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My 2014 5.3L 4WD Tahoe has developed a nasty habit of throwing P015B and P015D codes, O2 sensor Delayed Response – Lean to Rich, for sensor 1 on both banks. It happens on the first deceleration from highway speed when the coolant temperature is above 80C (176F). “D” comes on more often than “B”, it seems, however quite often they don't hesitate to come together.

When this first happened with P015D I quickly replaced the passenger-side O2 sensor hoping to be done with that ordeal, but no, the “D” and then “B” persisted.


Checked for vacuum and exhaust leaks with a smoke machine, everything seems to be tight. The exhaust manifolds look allright and not cracked, all bolts are in place.

Then I set my ScanGauge II to monitor fuel trims. It turns out that at the time the codes are thrown, I have a huge fuel enrichment on deceleration, on both banks, the short trims are in +30% range. This happens for a split second, then the code(s) are set, and then the short trims come back to normal. Long trims stay pretty much the same, and negative. This deceleration enrichment does not happen on any subsequent deceleration that I tried.

The Idle, 1500, and 2500RPM long term+short term trims are around zero, which confirms no air leak, at least.


I should get a good O2 readings graph, but the phone apps that I have attached to ELM327 interface don't really plot good ones. And my old trusted Maxidas scanner is still buried somewhere after we moved.

I'm puzzled why do I have that said enrichment, and where to look for a possible cause of these codes. Massive sudden air (or exhaust) leak when the semi-hot engine twists the mounts on deceleration? Weak gaskets from the exhaust manifold to the cats? Perhaps this enrichment is intentional, just for the O2 response test purposes?

This has been going for a while. The engine is stock and runs great. No increased fuel consumption. AFM is disabled through Diablo tuner. No noticeable oil consumption through ~10,000km oil change cycle. I don't tow.
Thank you for any help, gentlemen!
 
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