Draft guidance: awaiting Claude spot-check, qualified-mechanic review and named-editor approval. Do not use a fault code alone to replace parts.
P0140: Oxygen sensor circuit no activity detected, Bank 1 Sensor 2
The computer has not seen the expected response from the downstream Bank 1 sensor during its monitor.
What P0140 means
The computer has not seen the expected response from the downstream Bank 1 sensor during its monitor. The sensor may be inactive, but power, heater, wiring, connector or exhaust faults can create the same result.
Can I still drive?
This is generally a moderate rather than stop-now issue when the vehicle drives normally and the light is steady. Catalyst monitoring and emissions readiness may be unavailable, so arrange diagnosis soon. Stop if another symptom brings severe misfire, stalling, smoke or major power loss.
Symptoms
- Steady engine-management light
- Little or no change in drivability
- Failed emissions or readiness test
- Higher emissions if a broader control fault is present
Common causes
- Inactive, aged or contaminated downstream sensor
- Open or shorted signal or reference-earth circuit
- Melted, chafed, wet or corroded connector and harness
- Heater fault preventing timely operation
- Exhaust or mixture problem; catalyst or control-module faults are less common possibilities
Safe first checks
- Save codes and freeze-frame information, paying attention to P0141 or another heater code. Inspect the cold lead and connector, check the specified fuses and look for obvious exhaust leakage. Do not condemn the downstream sensor merely because its warm trace is steadier than the upstream trace; that can be normal.
Typical UK fix cost
About £90–£350 for diagnosis and a common electrical, leak or sensor repair. Confirmed lambda replacement commonly benchmarks at £110–£266; damaged wiring, threads or exhaust parts can raise the total.
Related models
This is a generic OBD-II code used across many makes and models. The exact test thresholds, component layout and repair route vary by engine and manufacturer, so check vehicle-specific technical information before ordering parts.
Related fault codes
- P0137: Oxygen sensor circuit low voltage, Bank 1 Sensor 2
- P0138: Oxygen sensor circuit high voltage, Bank 1 Sensor 2
- P0141: Oxygen sensor heater circuit malfunction, Bank 1 Sensor 2
- P0171: Fuel-trim system too lean, Bank 1
Sources
A diagnostic trouble code identifies a system or circuit to investigate. It does not prove that a named part has failed. Preserve freeze-frame data and seek a vehicle-specific diagnosis before clearing the code.