P015C
O2 Sensor Delayed Response - Rich to Lean (Bank 2 Sensor 1)P015C is a generic OBD-II powertrain diagnostic trouble code: O2 Sensor Delayed Response - Rich to Lean (Bank 2 Sensor 1). It is logged by the engine control unit when the o2/lambda monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P015C means
P015C is stored when the PCM detects that the upstream oxygen sensor on Bank 2 — the engine bank not containing cylinder #1 — takes too long to transition from a rich-indicating voltage to a lean-indicating voltage. This is the Bank 2 counterpart to P015A. The upstream (pre-catalyst) sensor is essential for accurate closed-loop fuel trim on that cylinder bank; when its rich-to-lean response is delayed beyond the PCM's threshold, the controller cannot pull fuelling back quickly enough during lean transitions, briefly over-enriching the mixture. This increases hydrocarbon emissions, reduces fuel economy, and over time can overload the Bank 2 catalytic converter with excess unburned fuel. Common root causes include a heat-degraded or contaminated sensor element, a failed heater circuit, and exhaust leaks that introduce ambient air. Because P015C mirrors P015A in all technical respects but for Bank 2, the diagnostic approach is identical — systematic elimination of exhaust leaks, wiring faults, and secondary fuelling codes before sensor replacement. The MIL is illuminated when the fault is confirmed.
Common causes
Most-frequently reported root causes when P015C is logged.
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1
Worn, oil-fouled, or contaminated Bank 2 Sensor 1 O2 sensor with a slow rich-to-lean electrochemical response
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2
Failed or degraded internal heater element in the Bank 2 upstream sensor
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3
Exhaust leak upstream of Bank 2 Sensor 1 injecting ambient air and masking the lean transition
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4
Burnt, corroded, or open-circuit wiring and connectors in the Bank 2 Sensor 1 circuit
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5
Dirty or faulty MAF sensor providing inaccurate air mass data affecting Bank 2 fuel delivery
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6
Leaking or stuck-open fuel injector on Bank 2 creating a persistent rich bias that stresses sensor response timing
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7
PCM calibration fault or software issue (rare, only after all hardware causes are eliminated)
Symptoms drivers notice
How to diagnose P015C
A typical diagnostic flow when this code is present.
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1
Scan all DTCs and note freeze frame conditions; repair any misfire, MAF, MAP, or TPS codes on Bank 2 first as they can cause secondary O2 faults
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2
Inspect Bank 2 Sensor 1 wiring harness for heat damage near exhaust pipes and shields, frayed insulation, and corroded connector pins
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3
Check for exhaust leaks upstream of Bank 2 Sensor 1 — manifold gasket, flex pipe, or downpipe joints — using a smoke machine or propane enrichment
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4
Monitor Bank 2 Sensor 1 voltage live at operating temperature; normal is regular oscillation 0.1–0.9 V; measure the delay from peak rich reading before the voltage begins to fall
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5
Test the O2 sensor heater circuit resistance across the heater pins and verify power supply voltage at the connector
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6
Compare Bank 1 and Bank 2 short-term and long-term fuel trims; significant disparity between banks can help confirm whether the fault is sensor-only or fuelling-related
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7
Replace Bank 2 Sensor 1 if delayed rich-to-lean transition is confirmed after eliminating exhaust leaks and wiring faults; clear codes and drive a full cycle to verify
Related powertrain codes
- P0040 — Upstream Oxygen Sensors Swapped From Bank To Bank
- P0041 — Downstream Oxygen Sensors Swapped From Bank To Bank
- P0130 — O2 Sensor Circuit Malfunction (Bank 1 Sensor 1)
- P0131 — O2 Sensor Circuit Low Voltage (Bank 1 Sensor I)
- P0132 — O2 Sensor Circuit High Voltage (Bank 1 Sensor 1)
- P0133 — O2 Sensor Circuit Slow Response (Bank 1 Sensor 1)
Frequently asked questions
Is P015C more common on V6/V8 engines than four-cylinders?
Yes. Bank 2 only exists on engines with two separate cylinder banks (V-type or flat/boxer engines). Four-cylinder engines are single-bank and will never produce a Bank 2 code. P015C is therefore exclusive to V6, V8, V10, and flat-engine vehicles.
Can P015C appear alongside P015A?
Yes. If both upstream sensors are aging simultaneously — which is common since they were installed at the same time — both P015A (Bank 1) and P015C (Bank 2) may appear together. In that case, replacing both upstream sensors is typically recommended.
How do I locate Bank 2 Sensor 1 on my vehicle?
Bank 2 is the cylinder bank not containing cylinder #1 — usually the passenger side on American V8s and many European V6s, but this varies by manufacturer. Sensor 1 is always the upstream sensor, located before the catalytic converter in the exhaust flow. A vehicle-specific repair manual will show the exact location.
Will P015C cause a failed MOT or emissions inspection?
Yes. An active P015C illuminates the MIL, which causes an automatic failure in most emissions and MOT-style inspections. The code must be resolved and monitors must complete a full drive cycle readiness check before the vehicle can pass.
Disabling P015C in software
RaceTune can permanently disable P015C — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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