Fix P015A: Mechanic’s solutions that WORKED

The code P015A: O2 Sensor Delayed Response – Rich to Lean (Bank 1 Sensor 1) points out a delay in the oxygen sensor’s response when switching from a rich to lean condition, and it is most likely caused by sensor malfunctions or issues in the air-fuel mixture.

P015A quick overview

Meaning	P015A: O2 Sensor Delayed Response – Rich to Lean (Bank 1 Sensor 1)
Is it serious?	Yes, it can affect fuel efficiency, emissions, and engine performance.
Possible causes	– Faulty or aging oxygen sensor – Vacuum leaks – Exhaust leaks near the oxygen sensor – Faulty fuel injectors – Contaminated or malfunctioning Mass Air Flow (MAF) sensor – Incorrect fuel pressure – Faulty Engine Control Module (ECM)
How to diagnose?	Scan for Codes: Use an OBD-II scanner to confirm P015A and check for other related codes. Visual Inspection: Check for any obvious signs of damage or wear on the oxygen sensor and its wiring. Check for Leaks: Inspect for vacuum and exhaust leaks, especially near the Bank 1 Sensor 1 oxygen sensor. Test the Oxygen Sensor: Using a digital multimeter or a scan tool, monitor the oxygen sensor’s voltage. It should fluctuate when the engine is running. Inspect the MAF Sensor: Check the Mass Air Flow sensor for contamination or damage. Check Fuel Pressure: Ensure that the fuel pressure is within the manufacturer’s specifications. Check for Software Updates: Some vehicles may have ECM software updates that address this issue. Replace Components as Needed: If diagnostics point to a faulty component (like the oxygen sensor), replace it.

How to fix P015A – learn from mechanics

I looked into P015A service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Chevrolet

2013 Chevrolet Sonic LTZ 1.4L

Issue + repair history:

• Check engine light on with occasional rough running.
• Previous repairs include replacing fouled spark plugs and upstream O2 sensor.
• Vehicle returned with the same codes after a few days.
• Observations indicate the vehicle might be running rich.

Other OBD2 codes + test results:

• p015a: upstream O2 sensor slow to switch
• p2096: cat at limit

What are people suggesting to fix the issue:

• Gather more data, especially from O2s, MAF, MAP.
• Check for a clogged catalytic converter.
• Perform an injector balance test.
• Check for vacuum leaks.
• Examine the PCV system, particularly the valve cover.
• Inspect the intake manifold for a missing check valve.

What was the final fix:

• The check valve in the intake manifold was missing.
• A new intake manifold was installed, resolving the issue.

Case #2: Nissan

2016 Nissan Altima S 2.5L

Issue + repair history:

• MIL lamp on, vehicle part of a fleet and mostly driven on highways.
• Vehicle well-maintained and other fleet vehicles haven’t shown similar issues.
• PCM updated twice, PCV updated, front A/F sensor warrantied during dealer service.
• Previous repairs: MAF cleaned and replaced, fuel pressure checked, front and rear O2 sensors replaced, PCM reflashed at Nissan dealer.

Other OBD2 codes + test results:

• P015b: O2 Sensor Delayed response – Lean to Rich Bank 1 Sensor 1
• P015a: O2 Sensor Delayed response – Rich to Lean Bank 1 Sensor 1
• P014d: O2 Sensor Slow response – Lean To Rich Bank 1 Sensor 1
• P014c: O2 Sensor Slow response – Rich To Lean bank 1 Sensor 1

What are people suggesting to fix the issue:

• Refer to TSB NTB16-117b for potential fixes including PCV valve replacement, ECM reprogramming, grille shutter modifications, and exhaust manifold cover replacement.
• Check for warranty-related issues and return to the dealer if necessary.
• Inspect for a faulty PCC valve or vacuum leaks.
• Consider the impact of under hood temperatures on A/F sensor failures, especially if the front plastic lower cover is modified.

What was the final fix:

• PCV was replaced, A/F sensor replaced twice, and dealer updated the software.

Advice	Brief Description of Diagnostic Step
Check for TSBs (Technical Service Bulletins)	Manufacturers often release bulletins related to specific issues. Always check if there’s a TSB related to the fault code.
Inspect PCV Valve/System	A faulty PCV system can cause various O2 sensor-related issues. Check its condition and replace if necessary.
Inspect O2/Air-Fuel (A/F) Sensors	Faulty or “lazy” O2 sensors can trigger the code. Monitor their performance and replace if they’re not switching as they should.
Check for Vacuum Leaks	Vacuum leaks can cause O2 sensors to read incorrectly. Inspect the system for any leaks.
Reprogram/Update the PCM/ECM	Sometimes, the vehicle’s computer software might need an update to address certain issues.
Inspect Exhaust System	A clogged or restricted exhaust, especially the DPF in diesel engines, can cause O2 sensor issues. Check for any blockages or restrictions.
Consider Driving Conditions	Vehicles that don’t heat the exhaust sufficiently due to short trips can accumulate more soot, affecting the O2 sensor readings.
Return to Dealer for Warranty Work	If the vehicle is still under warranty, consider returning it to the dealer for diagnostics and repairs.