Faulty Bank 1 Sensor 3 oxygen sensor (failed or contaminated element); Damaged, chafed or corroded wiring or connector to the sensor; Exhaust leak near the sensor affecting its reading; Open circuit or high resistance in the signal or ground wire; Sensor heater circuit fault or blown fuse or relay feeding the sensor (design dependent); Fault in the engine control unit or its sensor input.

P0146

O2 Sensor Circuit No Activity Detected 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
46: FaultThe specific fault in that area

What it means

P0146 is the generic code for no activity detected in the oxygen sensor circuit on Bank 1, Sensor 3. Sensor 3 is the third oxygen sensor on that bank, normally fitted downstream of the catalytic converter (often after a second catalyst or further along the exhaust). The control unit set the code because the signal stayed flat or did not change as expected during its monitoring test. Bank 1 is the side of the engine with cylinder number 1, and the number and position of sensors vary by model and engine.

Symptoms

Engine management light on
Usually no noticeable change in driving or performance
Possible failed emissions or MOT test
Other oxygen sensor or catalyst codes stored alongside
Fuel economy may be slightly affected in some cases

Possible causes

Faulty Bank 1 Sensor 3 oxygen sensor (failed or contaminated element)likely
Damaged, chafed or corroded wiring or connector to the sensorlikely
Exhaust leak near the sensor affecting its readingpossible
Open circuit or high resistance in the signal or ground wirepossible
Sensor heater circuit fault or blown fuse or relay feeding the sensor (design dependent)possible
Fault in the engine control unit or its sensor inputrare

How to diagnose

Read all stored and pending codes and note the freeze frame data (engine temperature, load, speed) from when the fault set
Confirm which sensor is Bank 1 Sensor 3 on this particular engine using the manufacturer's layout information, as positions vary by model
Visually inspect the sensor, wiring and connector for heat damage, chafing, water ingress and corrosion
Check for exhaust leaks upstream of and at the sensor, including joints and flanges
Check the relevant fuses and relays and the sensor heater supply and ground, following the wiring diagram for the vehicle
Watch the sensor's live data with the engine warm and compare it with the other oxygen sensors while changing engine load and speed
Test the wiring for continuity and short circuits between the sensor connector and the control unit
Check the sensor's heater resistance against the manufacturer's specification

How to fix

Replace Bank 1 Sensor 3 if it is confirmed faulty or contaminated, using the correct type for the engine
Repair or replace damaged wiring and clean or renew corroded connectors
Repair any exhaust leak affecting the sensor reading
Restore the sensor's power or ground supply by replacing a failed fuse or relay after finding why it failed
Diagnose and repair the control unit only after all wiring and sensor faults are ruled out, as this is rare

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. Book it in reasonably soon, as it may cause an emissions test failure and can hide other problems.

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