P015AO2 Sensor Delayed Response - Rich to Lean Bank 1 Sensor 1
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- The upstream oxygen sensor (sensor 1, before the catalytic converter) is the main control sensor for the air-fuel mixture. 'Delayed response' means the sensor starts reacting too late, or does not reach the target level at all, after the mixture has changed. This code covers the rich-to-lean direction, usually tested during deceleration fuel cut-off. GM uses this on switching (narrow-band) sensors: while the fuel cut-off for the downstream tests is running, it measures how long the upstream sensor takes to start dropping from above 680 mV and fails a filtered delay above about 0.58 s after one trip. Conditions include warm engine, 40–78 mph and a hot converter. CARB requires separate detection of slow and delayed faults in each direction (phased in from 2009 for downstream and 2011 for upstream sensors).
- What you may notice
- Check engine light on
- Slightly higher consumption or rough idle possible
- Higher emissions, possible emissions test failure
- Often no noticeable symptoms
- Likely causes
- LikelyUpstream oxygen sensor aged or poisoned (silicone, oil, coolant, soot)
- PossibleExhaust leak ahead of the sensor (manifold, flange)
- RareMixture fault: intake air leak, injectors, fuel pressure, air flow sensor
- RareSensor heater weak, sensor too cold
- RareConnector, wiring or control module software
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €80 – €300
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.