P015D
O2 Sensor Delayed Response - Lean to Rich Bank 2 Sensor 1.
- Generic
- Powertrain
- Generic code
- Low severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 1
- AreaFuel and air metering
- 5D
- FaultThe specific fault in that area
What it means
P015D means the engine control unit has seen the upstream oxygen sensor on bank 2 (sensor 1) react too slowly when the mixture swings from lean to rich. The sensor signal is taking longer than expected to move, so the ECU can no longer trust it for accurate fuel trim control. This is a generic SAE definition, and the exact test conditions and thresholds vary by manufacturer and engine.
Symptoms
- Engine warning light on
- Slightly higher fuel consumption
- Rough or unstable idle in some cases
- Hesitation or poor throttle response
- Failed emissions test
- Fuel trim faults stored alongside this code
Possible causes
- Ageing, contaminated or sluggish bank 2 upstream oxygen sensor (carbon, oil, coolant or silicone contamination)likely
- Exhaust leak upstream of or near the bank 2 sensor letting in false airpossible
- Damaged wiring, poor connector contact or corrosion in the sensor circuit, including heater circuit faultspossible
- Fuel delivery or mixture problem on bank 2, such as a leaking or clogged injector or a vacuum leakpossible
- Engine misfire or oil/coolant burning on bank 2 contaminating the sensorrare
- Faulty engine control unit or outdated calibration (only where the manufacturer has a known issue)rare
How to diagnose
- Read all stored codes and freeze frame data, noting engine temperature, load and fuel trim values when the fault set
- Check for other related codes such as misfires, fuel trim, heater circuit or other oxygen sensor faults and deal with those first
- Inspect the bank 2 sensor wiring, connector and plug for damage, heat melting, oil or water ingress and corrosion
- Check the exhaust manifold, flexible joints and gaskets upstream of the sensor for leaks
- Check for vacuum leaks and inspect intake hoses and connections
- With a scan tool, view live oxygen sensor data on bank 2 and compare switching speed with bank 1 at idle and steady cruise
- Check short and long term fuel trims on both banks to find a mixture imbalance
- Check the sensor heater circuit resistance and supply against the manufacturer's specification, and check for any applicable software updates for your model
How to fix
- Replace the bank 2 upstream oxygen sensor if live data and testing show it is slow or faulty
- Repair or replace damaged wiring, connectors or terminals
- Repair exhaust leaks near the sensor by renewing gaskets or damaged pipe sections
- Fix vacuum leaks or faulty injectors causing the mixture fault on bank 2
- Cure the source of contamination, such as misfire, oil consumption or a coolant leak, before fitting a new sensor
- Apply a manufacturer calibration update only if a known fault with the existing software is confirmed
Can I keep driving?
Low severity
The car can normally be driven short term while you book it in, though economy and emissions may suffer. If it runs poorly or misfires, have it checked sooner to avoid catalytic converter damage.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.