Failed heater element inside the Bank 2 Sensor 3 oxygen sensor; Damaged, chafed or melted wiring to the sensor heater, shorted to earth, often near the exhaust; Corroded, loose or contaminated connector at the sensor; Blown fuse or faulty relay supplying the oxygen sensor heater circuit, depending on model; Wrongly identified sensor position, so the wrong sensor was fitted or the wiring was incorrectly repaired; Fault in the engine control unit heater driver.

P0063

HO2S Heater Control Circuit Low Bank 2 Sensor 3.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
0: AreaFuel and air metering, auxiliary emission controls
63: FaultThe specific fault in that area

What it means

P0063 means the engine control unit has detected a low signal in the heater control circuit of the heated oxygen sensor on Bank 2, Sensor 3. Sensor 3 is normally a further downstream sensor, fitted after the catalytic converter or after a second catalyst on engines that have one. The control unit saw the heater circuit voltage or current lower than expected, which points to a short to earth, high resistance or a fault in the heater or its driver.

Symptoms

Engine warning light on
Usually no noticeable change in driveability
Possible slight increase in fuel consumption on some models
Other oxygen sensor or catalyst monitor codes stored alongside it
Emissions readiness monitors not completing, which may cause an MOT failure

Possible causes

Failed heater element inside the Bank 2 Sensor 3 oxygen sensorlikely
Damaged, chafed or melted wiring to the sensor heater, shorted to earth, often near the exhaustlikely
Corroded, loose or contaminated connector at the sensorpossible
Blown fuse or faulty relay supplying the oxygen sensor heater circuit, depending on modelpossible
Wrongly identified sensor position, so the wrong sensor was fitted or the wiring was incorrectly repairedpossible
Fault in the engine control unit heater driverrare

How to diagnose

Read all stored and pending codes and freeze frame data, and note any related heater or sensor codes for other positions
Confirm which sensor is Bank 2 Sensor 3 on this engine using the manufacturer's layout, as the numbering depends on the model
Visually inspect the sensor wiring and connector for heat damage, chafing, corrosion and water ingress
Check the relevant fuse and relay, if fitted, and the power supply to the heater circuit with the ignition on
Measure the heater element resistance at the sensor and compare it with the manufacturer's specification
Check the heater control wire for a short to earth and for continuity back to the control unit with the connector unplugged
Monitor the heater duty cycle or sensor response with a scan tool once the engine is running and warm
Clear the code and road test to confirm it does not return

How to fix

Replace the Bank 2 Sensor 3 oxygen sensor if the heater element is open circuit or out of specification
Repair or replace damaged wiring, ensuring it is routed away from hot exhaust parts and secured properly
Clean or replace a corroded or damaged connector and terminals
Replace the faulty fuse or relay, and find out why it failed
Repair or replace the engine control unit only after the wiring, power supply and sensor have all been proven good

Can I keep driving?

Low severity

The car is normally safe to drive as this is a downstream sensor heater fault, but book it in soon so the emissions monitoring and MOT readiness are not affected. Have it checked promptly if other warning lights or driveability problems appear.

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