P0140 Oxygen sensor circuit no activity detected (bank 1, sensor 2)
What P0140 means
The engine computer expected the downstream oxygen sensor on bank 1 to produce a signal once the engine was warm, but the signal stayed flat. It cannot monitor the catalytic converter without it.
P0140 is a generic SAE J2012 code: it means the same on every make. The exact cause still depends on the car, so read the freeze-frame data before replacing parts.
At a glance
- Severity
- Medium
- Typical repair cost
- 60–300 €
- Workshop time
- 0.3–1.5 h
- Repair difficulty
- Easy
- DIY possible
- Yes
- Check engine light
- Yes
- Affects emissions test
- Yes
Parts and labour at an independent workshop in Europe. Main dealers charge more; the cause decides the bill, not the code.
Symptoms
- Check engine light on
- Usually no noticeable change in how the car drives
- Catalyst readiness monitor not completing
- Possible failed emissions test at inspection
Common causes
- Dead downstream oxygen sensor
- Open signal wire or unplugged connector
- Failed sensor heater keeping the sensor too cold
- Wiring melted against the exhaust
Can I keep driving with P0140?
You can keep driving, but have it checked within one to two weeks. The engine is rarely affected, but the catalyst check cannot run and the car may fail its emissions inspection.
What to check first
- Check for a heater code for the same sensor and repair that first.
- Make sure the connector is plugged in and the wiring is intact along the exhaust.
- Watch the live signal on a fully warm engine after a few minutes of driving.
- Replace the downstream oxygen sensor if the wiring is good but the signal stays flat.
Related codes
- P0141 Oxygen sensor heater circuit (bank 1 sensor 2)
- P0139 Oxygen sensor circuit slow response (bank 1, sensor 2)
- P0138 Oxygen sensor circuit high voltage (bank 1, sensor 2)
- P0137 Oxygen sensor circuit low voltage (bank 1, sensor 2)
- P0136 Oxygen sensor circuit (bank 1, sensor 2)
- P0135 Oxygen sensor heater circuit (bank 1, sensor 1)
- P0134 Oxygen sensor circuit no activity detected (bank 1, sensor 1)
- P0133 Oxygen sensor slow response (bank 1 sensor 1)
Data: TORKO fault-code catalogue, built on OBDex (CC0-1.0) and reviewed against workshop practice. Informational only — it does not replace a diagnosis by a mechanic.
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