P0140
O2 Sensor Circuit No Activity Detected Bank 1 Sensor 2.
- 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
- 40
- FaultThe specific fault in that area
What it means
P0140 means the engine control unit has found no activity in the Bank 1 Sensor 2 oxygen sensor circuit, which is the sensor downstream of the catalytic converter on the bank containing cylinder 1. The control unit saw a signal that stayed flat, open circuit or stuck at a fixed value instead of switching or varying as expected once the engine was warm and running.
Symptoms
- Engine warning light on
- Usually no noticeable change in driving
- Possible failed emissions test
- Occasional slight change in fuel economy in some cases
- Other exhaust-related codes stored alongside it
Possible causes
- Failed or aged downstream oxygen sensor (Bank 1 Sensor 2)likely
- Damaged, chafed, melted or corroded sensor wiring or connectorlikely
- Open circuit in the sensor heater circuit or its fuse or relay, where the sensor design depends on itpossible
- Exhaust leak near the sensor affecting readingspossible
- Poor connection or fault in the signal or ground wire between sensor and control unitpossible
- Fault within the engine control unitrare
How to diagnose
- Read the stored codes and freeze frame data to see engine temperature, load and speed when the fault set, and note any other codes.
- Check for related heater circuit codes or fuse and relay faults that could point to a power supply problem.
- Visually inspect the sensor wiring and connector from the sensor to the harness, looking for heat damage, chafing, water ingress and corrosion.
- Inspect the exhaust around the catalytic converter and sensor for leaks, cracks or loose joints.
- With the engine warm, view live data for Bank 1 Sensor 2 and check whether the signal moves, or sits at a fixed value.
- Check the sensor heater resistance and supply voltage against the manufacturer's specification for that model.
- Test the signal and ground wires for continuity, shorts and resistance back to the control unit connector.
- If wiring and sensor checks pass, check for a control unit software update relevant to this code for the specific vehicle.
How to fix
- Replace the downstream oxygen sensor if it is faulty or not responding.
- Repair or replace damaged wiring or the connector, using proper soldered and sealed joints.
- Replace a blown fuse or faulty relay after finding why it failed.
- Repair any exhaust leak affecting the sensor area.
- Clean or repair corroded terminals and restore a good connection.
- Apply a manufacturer calibration update only if an outdated calibration is a known cause for that model.
Can I keep driving?
Low severity
The car can normally be driven while you book it in, as this fault rarely affects drivability. Fix it soon, as it may cause an emissions test failure and could hide other developing problems.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.