P0155
O2 Sensor Heater Circuit (Bank 2 Sensor 1)
- Severity
- Medium
- Driving
- Drivable — book it in
The heater circuit in the upstream oxygen sensor on bank 2 has a fault. Oxygen sensors only work once hot, so each one contains a small heating element to bring it up to temperature quickly after start-up. With the heater dead the sensor takes far longer to start working, or never works at low load, so the engine runs on a default fuel calculation instead.
Possible causes
- CommonFailed heater element inside the sensor - the sensor must be replaced
- CommonBlown fuse on the heater circuit
- PossibleDamaged heater wiring or connector
- RareRelay or module driver fault on the heater circuit
What you might notice
- Check engine light on
- Worse fuel economy, particularly on short journeys
- Rough running when cold that improves as the engine warms
- Failed emissions test
What to check, in order
- Check the fuse for the oxygen sensor heater circuit. This is the cheapest possible cause and worth eliminating first.
- Measure the resistance of the heater element at the sensor connector and compare it against specification. An open circuit means the sensor needs replacing.
- Inspect the wiring and connector for heat damage - these run near the exhaust.
- If several heater codes appear at once, suspect the shared fuse or relay rather than several failed sensors.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx
Fuel and air metering
P0100P0101P0102P0103P0104P0105P0106P0107P0108P0109P0110P0111P0112P0113P0114P0115P0116P0117P0118P0119P0120P0121P0122P0123P0124P0125P0126P0127P0128P0129P0130P0131P0132P0133P0134P0135P0136P0137P0138P0139P0140P0141P0142P0143P0144P0145P0146P0147P0148P0149P0150P0151P0152P0153P0154P0155P0156P0157P0158P0159P0160P0161P0162P0163P0164P0165P0166P0167P0168P0169P0170P0171P0172P0173P0174P0175P0176P0177P0178P0179P0180P0181P0182P0183P0184P0185P0186P0187P0188P0189P0190P0191P0192P0193P0194P0195P0196P0197P0198P0199