P015B and P015D GM 5.3L

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Apr 6, 2004
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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 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.
Thank you for any help, gentlemen!
 
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Jul 16, 2005
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Montague, NJ
I'd suspect the MAP sensor as it senses manifold vacuum. I chased an MPG loss on my '11 5.3 . Like 3-4 mpg. No codes set in any of the code families. My Autoenginuty scan tool has 2 MAP sensor tests, and my MAP would erratically fail one of the tests. EM would not fully run EVAP monitors either.
Also real time MPG dash screen on mine would not go up into the 90 mpg range on a downhill off throttle coast. That's what got me to look into the MAP sensor. New MAP cured it.
 

yugrus

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Thank you 54! Although my MAP does report seemingly correct manifold pressures (up to 13.5psi at hard accel, ~3.5 at idle and ~2 at hard decel), I will definitely look into testing it. Fuel economy reports correct 0L/100km at long deceleration at highway speed, so the fuel shuts off, again, seemingly.
 
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Nice post!

The enrichment is intentional.....Then the fuel injectors are shut off (decel fuel cut-off), The O2 sensor response from rich to lean should be instantaneous, If the transition time is longer than the predetermined value.....P015B &/or P015D will set.

A upstream O2 replacement will generally fix the DTC/s because what the test does....Tests the transition response time of the O2.

I'm assuming that your not losing any coolant or have excessive oil consumption??

Do the DTC's appear later on in the Oil Change Interval?? .....Could have fuel diluting the oil.

I've seen a few cases where these codes are a precursor to more serious Fuel Injector issues in GM Ecotec3 engines.....Where you have misfires & high fuel trims.

All the ECM knows is that it forced a rich condition & shutting off the injectors didn't immediately drive the O2 lean.
 
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Did you use a OE O2 sensor? I’d start there. Or Perhaps there’s an update for these things at the dealer? Although I haven’t heard anything.

I had a 2018. Something just wasn’t right with the fuel system on it. Fuel trims were -20 on it when it was warming up, then it’d go somewhat normal. Had a specific cylinder random misfire code cylinder 5 or 7 I think, (but it wasn’t an AFM cylinder). Everything checked out. Had occasional power loss/hesitation under light load AFTER A DECELERATION climbing hills at highway speeds. Deceleration was something I absolutely feared with my 5.3 2018 Silverado. It just never could handle a deceleration event. It couldn’t recover from it. A delay, a misfire, a fish biting sensation. I was using around 3/4’s of a quart of oil between 5,000 mile oil changes.

Misfire data would show random misfires all over the place, with suspected cylinder worse. I assumed fuel injector. Forums are plentiful with fuel injector replacements on these things. Back ordered. Have to be specific on the type of injector you order because they made a few different ones. I traded it in with 50,000 miles on it.

Your circumstance sounds more like a O2 sensor. I know you already replaced it but if it’s not OE I’d probably start there.
 

yugrus

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Thank you, guys!
I indeed replaced O2 sensor with Delco one.
clinebarger, thank you for confirmation that enrichment is intentional. However, the problem is actually reverse- slow from Lean to Rich. So yeah, it looks like it would only enrich for the testing purposes, as it doesn't do it on subsequent decelerations (coasting).

No coolant loss, nor visible oil consumption between OCI of slightly less than 6K miles. The codes come up irregardless of OCI, I've recently changed the oil.

So far I'm planning to investigate the exhaust gaskets before cats, after it warms up a bit here and the snow goes away... Gotta be an exhaust leak somewhere!
 
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The Exhaust Flange Gaskets aren't really known to cause issues, But broken Exhaust Manifold to Cylinder Head Bolts are a wide spread issue on all Gen III, IV, & V engines. Although....The exhaust leak will usually seal itself once warmed up unless you have more than one manifold bolt broken in series.
 

wtd

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Have you checked power, grounds, and signal voltage to both upstream O2's?

Did you do your smoke tests when the vehicle was cold?
 

yugrus

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I did the smoke test with the engine off for 24hr+. Haven't thought of an actual voltage check, as both are reporting proper values in expected time intervals, from what I can see..
 
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