P0140 on Mercedes-Benz: Causes, Symptoms and Fix Cost
Quick Answer
Safe to drive (short-term)
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.
- Severity
- Moderate · Emissions
- Typical repair cost, all makes
- €1-€310
Connect a standard OBD2 adapter (Bluetooth LE on iPhone) to your Mercedes-Benz and Skanyx tells you what P0140 means on that engine, whether it is safe to keep driving, and what the fix should cost. Free on iPhone and Android.
Get Skanyx freeWhat does P0140 mean on a Mercedes-Benz?
The Quick Answer above is the generic definition. What follows is the model-specific detail for the Mercedes-Benz models that log P0140.
Mercedes C-Class
2007-2024
On the W204 C-Class with the M271 1.8 Kompressor petrol, P0140 commonly comes from heater element burnout on a high-mileage sensor, or from a broken signal wire. Diesel C-Class models use a different exhaust sensor arrangement, so confirm the engine before ordering parts. The sensor runs roughly 70 to 220 euros depending on where you buy it.
What causes P0140 on a Mercedes-Benz?
Beyond the generic causes listed on the main P0140 page, these are the patterns noted for Mercedes-Benz models:
Heater burnout on the W204 M271 at high mileage
: Mercedes C-Class
Chafed or broken sensor signal wire
: Mercedes C-Class
How to diagnose P0140 on a Mercedes-Benz with OBD2
- Read freeze frame data and check for a heater code for the same sensor (P0141), which points to a power or heater problem at the sensor. Several heater codes at once (for example P0135 and P0141) point to a shared fuse or supply
- 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.
| Repair | Parts Cost | Labor Cost | Total Estimate | DIY Difficulty |
|---|---|---|---|---|
| Replace downstream O2 sensor (Bank 1, Sensor 2) | €40–€180 | €50–€130 | €90–€310 | Moderate |
| Repair O2 sensor wiring or connector | €5–€25 | €40–€120 | €45–€145 | Moderate |
| Replace heater fuse and diagnose underlying short | €1–€10 | €0–€80 | €1–€90 | Easy |
Prices estimated as of October 2026. Costs vary by region, vehicle, and shop.
Codes related to P0140
These codes are often seen alongside P0140 or point to related issues, on any make:
Looking for the full P0140 reference (all makes, full diagnosis flow, complete repair cost matrix)? See the main P0140 guide