P0140 means the ECU cannot detect any activity from the downstream oxygen sensor on Bank 1 (post-catalyst, Sensor 2). The sensor voltage is either flatlined or out of range. This usually points to a failed sensor, an open circuit in the wiring, or a connector that has come loose or corroded.
DTC/P0140·BMW
P0140 on BMW: Causes, Symptoms and Fix Cost
Quick Answer
Moderate SeveritySafe to drive (short-term)BMW
P0140 on a BMW means the ECU cannot detect any activity from the downstream oxygen sensor on Bank 1 (post-catalyst, Sensor 2). The sensor voltage is either flatlined or out of range. This usually points to a failed sensor, an open circuit in the wiring, or a connector that has come loose or corroded.
Repair cost on BMW€1 - €434
What does P0140 mean on a BMW?
BMW 3 Series
2006–2024On N52 and N55, the downstream sensor connector clip is fragile and frequently breaks on older cars. A broken clip lets the connector vibrate loose, which presents as P0140 (no activity) even though the sensor itself is fine. Inspect and re-secure the connector before condemning the sensor. BMW OEM Bosch sensors 110–200 euros, aftermarket Bosch around 60–110 euros.
What causes P0140 on a BMW?
Beyond the generic causes listed on the main P0140 page, these are the BMW-specific patterns we see most often:
BMW 3 SeriesBroken connector clip on N52/N55 causing intermittent disconnection
BMW 3 SeriesHeater element burnout at 150,000+ km producing flat signal
How to diagnose P0140 on a BMW with OBD2
Follow these steps to pinpoint the root cause of P0140:
- Read freeze frame data and check for companion heater codes (P0141, P0155) that would point to a power issue at the sensor
- Inspect the Bank 1 Sensor 2 connector visually for disconnection, corrosion, water intrusion, or melted plastic
- Use a multimeter at the sensor connector to verify ground, heater power (battery voltage with key on), and signal continuity back to the ECU
- If wiring tests good, unplug the sensor and measure heater resistance directly. Healthy: 2–15 ohms. Open: burned-out heater. The sensor needs replacement
- If a new sensor still shows no activity, scope the signal wire for opens or shorts between the sensor and ECU
How much does P0140 cost to fix on a BMW? (EUR)
Estimated repair costs on a BMW (BMW parts and labour typically run 40% above the average for this code).
Prices estimated as of May 2026. Costs vary by region, vehicle, and shop.
Related codes that often appear with P0140 on BMW
These codes commonly cluster with P0140 on BMW vehicles:
FAQ: P0140 on BMW
What does no activity detected mean?
The ECU expects the downstream O2 sensor signal to move within a defined range over time. If the voltage stays flat or out of range for the full monitor window, the ECU concludes the sensor has no activity and sets P0140. Most often the sensor itself has failed internally, or a wire has broken.
Can I drive with P0140?
Yes, short term. The downstream sensor does not drive fuel mixture, so the car runs normally. Long term you lose catalytic converter monitoring, which means you may miss a developing converter problem until it is severe.
How do I test an O2 sensor with a multimeter?
Unplug the sensor and measure heater resistance (typically 2–15 ohms). Plug it back in and back-probe the signal wire. With the engine warm and idling, a healthy downstream sensor reads around 0.6–0.8V steady. A flat reading at 0V or 5V with engine running points to an internal sensor failure.
Can a blown fuse cause P0140?
Indirectly yes. If the heater fuse is blown, the sensor never reaches operating temperature and stays inactive, triggering P0140 alongside heater codes like P0141. Check the heater fuse first if you see both code types.
Looking for the full P0140 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0140 guideSkanyx · BMW
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