Failed heater element inside the bank 2 sensor 1 oxygen sensor; Damaged, chafed or corroded wiring to the sensor heater, including open circuit or short to earth or supply; Corroded, loose or contaminated sensor connector; Blown fuse or faulty relay supplying the oxygen sensor heater circuit (layout depends on the model); Exhaust leak or heat damage near the sensor affecting the sensor or its harness; Fault in the engine control unit heater driver.

P0155

O2 Sensor Heater Circuit 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
55: FaultThe specific fault in that area

What it means

P0155 means the engine control unit has detected a fault in the heater circuit of the oxygen sensor fitted upstream of the catalytic converter on bank 2, the side of the engine opposite cylinder 1. The heater brings the sensor up to working temperature quickly so closed-loop fuel control can start. The code sets when the heater circuit current, voltage or resistance falls outside the expected range, or the sensor fails to warm up in the time allowed.

Symptoms

Engine warning light on
Slightly higher fuel consumption
Rough or unstable idle, particularly on a cold start
Hesitation or poor running while the engine warms up
Failed emissions test
Other oxygen sensor or fuel trim codes stored alongside

Possible causes

Failed heater element inside the bank 2 sensor 1 oxygen sensorlikely
Damaged, chafed or corroded wiring to the sensor heater, including open circuit or short to earth or supplylikely
Corroded, loose or contaminated sensor connectorpossible
Blown fuse or faulty relay supplying the oxygen sensor heater circuit (layout depends on the model)possible
Exhaust leak or heat damage near the sensor affecting the sensor or its harnesspossible
Fault in the engine control unit heater driverrare

How to diagnose

Read all stored and pending codes and note the freeze frame data, including engine temperature and running time, then check for other oxygen sensor or fuel trim codes.
Confirm which side is bank 2 for this engine, as the layout varies between models and engines, and identify sensor 1 as the one before the catalytic converter.
Inspect the sensor wiring and connector for melted insulation, chafing, exhaust heat damage, oil contamination and corrosion.
Check the fuse and relay for the oxygen sensor heater circuit using the wiring diagram for the vehicle.
Measure the heater resistance across the sensor heater terminals with the sensor unplugged and compare it with the manufacturer's specification.
With the connector disconnected and the ignition on, check the heater supply voltage and the control or earth side for continuity and shorts, following the wiring diagram.
Use live data to watch the sensor's warm-up behaviour and heater activity from a cold start, if the system reports them.
Check the exhaust for leaks close to the sensor that could affect readings or indicate heat damage.

How to fix

Replace the bank 2 sensor 1 oxygen sensor if the heater element is open circuit or out of specification.
Repair or replace damaged wiring and terminals in the heater circuit, protecting the harness away from exhaust heat.
Clean or replace a corroded or damaged connector and make sure it locks securely.
Replace the blown fuse or faulty relay only after finding and fixing the cause of the failure.
Repair any exhaust leak near the sensor and then clear the code and road test to confirm it does not return.
If all wiring and the sensor test fine, have the engine control unit driver circuit diagnosed and repaired or replaced.

Can I keep driving?

Low severity

The car can usually be driven short term as it will run in a degraded fuel control mode, but book it in soon. Prolonged driving may raise fuel use and emissions, and can mask other developing problems.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.