The Quick Answer above is the generic definition. What follows is the model-specific detail for the Mercedes-Benz models that log P0155.
DTC/P0155·Mercedes-Benz
P0155 on Mercedes-Benz: Causes, Symptoms and Fix Cost
Quick Answer
Low SeveritySafe to drive (short-term)Mercedes-Benz
P0155 on a Mercedes-Benz means the internal heater of the upstream oxygen sensor on bank 2 has failed or lost its power or ground, so the sensor takes longer to reach working temperature after a cold start. Bank 2 is the half of a V6, V8 or flat-six engine that does not contain cylinder 1 (a few inline-sixes with a split exhaust, such as BMW's M54, also have one). It is the same fault as P0135 on the other bank. The usual cause is a burned-out heater inside the sensor, though a blown fuse or damaged wiring can do the same.
Typical repair cost, all makes€1 - €320
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Mercedes-Benz C-Class (V6)
2005-2011On Mercedes V6 and V8 engines, including the M272 V6 in the C 230, C 280, C 300 and C 350, bank 1 is the right-hand side of the engine and bank 2 the left-hand side, viewed in the direction of travel, whichever side the steering wheel is on. Each bank has its own upstream sensor ahead of its catalytic converter. P0155 therefore concerns the heater of the left-hand pre-cat sensor. If the right-hand sensor's heater code (P0135) is stored as well, check the shared supply before replacing both sensors.
What causes P0155 on a Mercedes-Benz?
Beyond the generic causes listed on the main P0155 page, these are the patterns noted for Mercedes-Benz models:
Mercedes-Benz C-Class (V6)Burned-out heater in the left-hand (bank 2) pre-cat sensor on the M272 V6
Mercedes-Benz C-Class (V6)Heat-damaged plug on the left-hand sensor
How to diagnose P0155 on a Mercedes-Benz with OBD2
Follow these steps to pinpoint the root cause of P0155:
- Read all stored codes. If other heater codes (P0135, P0141, P0161) are stored too, suspect a shared fuse, relay or wiring fault rather than one sensor
- Check the O2 sensor heater fuse and replace it if blown, then find out why it blew before condemning the sensor
- Unplug the bank 2 upstream sensor and measure resistance across its two heater pins. A healthy heater usually reads a few ohms; check the specification for your engine. An open circuit means the heater has burned out
- With the key on, back-probe the harness plug and confirm battery voltage on the heater supply wire. No voltage points to a fuse, relay or wiring fault upstream of the sensor
- Inspect the connector and the wiring run for corrosion, melted insulation and chafing against the exhaust
- Replace the sensor if the heater reads open or out of range, clear the code and confirm it stays off after a cold start and warm-up
How much does P0155 cost to fix on a Mercedes-Benz? (EUR)
Estimated repair costs for P0155 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.
Codes related to P0155
These codes are often seen alongside P0155 or point to related issues, on any make:
Looking for the full P0155 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0155 guideSkanyx · Mercedes-Benz
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