The Quick Answer above is the generic definition. What follows is what is documented for the Mercedes-Benz models that log P0140, checked against manufacturer data and owner reports.
DTC/P0140·Mercedes-Benz
P0140 on Mercedes-Benz: Causes, Symptoms and Fix Cost
Quick Answer
Moderate SeveritySafe to drive (short-term)Mercedes-Benz
P0140 on a Mercedes-Benz 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 Mercedes-Benz€1 - €310
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Mercedes C-Class
2007–2024The W204 M271 1.8L Kompressor commonly triggers P0140 from heater element burnout around 130,000–150,000 km. The W205 OM651 diesel has the documented harness chafing point near the gearbox mount that can sever the signal wire, producing P0140. Mercedes-OEM Bosch sensors 130–220 euros, aftermarket Bosch around 70–120 euros.
What causes P0140 on a Mercedes-Benz?
Beyond the generic causes listed on the main P0140 page, these are the documented Mercedes-Benz-specific patterns:
Mercedes C-ClassHeater burnout on W204 M271 at 130,000+ km
Mercedes C-ClassHarness chafing on W205 OM651 severing signal wire
How to diagnose P0140 on a Mercedes-Benz 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 Mercedes-Benz? (EUR)
Estimated repair costs for P0140 in EUR, compiled across makes. Expect Mercedes-Benz parts and labour towards the upper end of each range.
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
Related codes that often appear with P0140 on Mercedes-Benz
These codes commonly cluster with P0140 on Mercedes-Benz vehicles:
Looking for the full P0140 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0140 guideSkanyx · Mercedes-Benz
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