Failed or aged Bank 1 Sensor 3 oxygen sensor, including a faulty internal heater; Damaged, chafed or burnt wiring to the sensor, often near the exhaust; Corroded, loose or contaminated connector or terminals at the sensor; Blown fuse or faulty heater supply or relay feeding the sensor heater circuit (depends on model); Exhaust leak near the sensor affecting its readings; Sensor contaminated by oil, coolant or silicone, or by fuel additives; Fault in the engine control unit or its sensor circuit driver.

P0142

O2 Sensor Circuit Bank 1 Sensor 3.

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
42: FaultThe specific fault in that area

What it means

P0142 is the generic code for a fault in the oxygen sensor circuit for Bank 1, Sensor 3, which is the third sensor along the exhaust on the side of the engine containing cylinder 1. This sensor is normally fitted downstream of the catalytic converter, and on some layouts it sits after a second catalyst. The control unit set the code because the sensor's signal or heater circuit was outside the expected range, stuck, or too slow to respond. Sensor numbering and position vary by model and engine, so confirm the layout for the vehicle in question.

Symptoms

Engine management light on
Usually no noticeable change in driveability
Possible slight increase in fuel consumption on some vehicles
Failed emissions test or MOT emissions concern
Other oxygen sensor or catalyst codes stored alongside it

Possible causes

Failed or aged Bank 1 Sensor 3 oxygen sensor, including a faulty internal heaterlikely
Damaged, chafed or burnt wiring to the sensor, often near the exhaustlikely
Corroded, loose or contaminated connector or terminals at the sensorpossible
Blown fuse or faulty heater supply or relay feeding the sensor heater circuit (depends on model)possible
Exhaust leak near the sensor affecting its readingspossible
Sensor contaminated by oil, coolant or silicone, or by fuel additivesrare
Fault in the engine control unit or its sensor circuit driverrare

How to diagnose

Read all stored and pending codes and note any related oxygen sensor, catalyst, misfire or fuelling codes.
Review freeze frame data to see engine load, temperature and speed when the code set, then check whether the fault returns after clearing it.
Confirm which sensor is Bank 1 Sensor 3 on this model and engine, using the manufacturer's exhaust layout information.
Inspect the sensor wiring and connector for heat damage, chafing, water ingress, corrosion and bent or pushed-back pins.
Check for exhaust leaks around the sensor and upstream joints.
View live sensor data and compare the signal behaviour with specification for the engine, once warm.
Measure heater circuit supply, earth and resistance against the manufacturer's figures, and check the related fuse.
Test the wiring for continuity and shorts between the sensor and the control unit before condemning the sensor or unit.

How to fix

Repair or replace damaged wiring and terminals, using proper sealed repairs.
Clean or replace a corroded or damaged connector.
Replace the Bank 1 Sensor 3 oxygen sensor if its signal or heater fails testing.
Replace a blown fuse or faulty relay after finding why it failed.
Repair any exhaust leak near the sensor.
Replace the control unit only if all wiring and sensor tests are good and the fault is confirmed in the unit.

Can I keep driving?

Low severity

The car can normally be driven while you arrange a repair, as this fault rarely affects safety or causes immediate damage. Do not leave it for long, as it may fail an emissions test and can hide other developing faults.

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