P0156 on Mercedes-Benz: Causes, Symptoms and Fix Cost

The Quick Answer above is the generic definition. What follows is the model-specific detail for the Mercedes-Benz models that log P0156.

Beyond the generic causes listed on the main P0156 page, these are the patterns noted for Mercedes-Benz models:

Follow these steps to pinpoint the root cause of P0156:

1. Confirm which sensor the code means before buying parts: Bank 2 is the cylinder bank that does not contain cylinder 1, and Sensor 2 is the one after the catalytic converter. Check the cylinder numbering for your engine in the service information, because the side of the car bank 2 sits on is not the same on every engine
2. Read freeze frame data to capture the engine conditions when the code was set (RPM, coolant temp, load) and note companion codes such as P0430, P0157-P0161 or the bank 1 equivalent P0136
3. Inspect the exhaust between the bank 2 catalytic converter and the downstream sensor for cracks, loose clamps or leaking gaskets
4. Inspect the Bank 2 Sensor 2 connector and wiring for corrosion, heat damage or chafing against the exhaust or heat shields
5. With the engine warm, view live data for both downstream sensors. A healthy downstream sensor holds a relatively flat voltage around 0.6-0.8V rather than switching rapidly like the upstream sensor, and the bank 1 and bank 2 downstream readings should behave in a similar way
6. On engines with a switching (narrowband) upstream sensor, a bank 2 downstream sensor that copies the switching of its upstream sensor means the bank 2 converter is likely failing. If it is erratic or stuck while the bank 1 downstream sensor looks normal, the sensor or its wiring is the likely fault

Estimated repair costs for P0156 in EUR, compiled across makes. Expect Mercedes-Benz parts and labour towards the upper end of each range.

These codes are often seen alongside P0156 or point to related issues, on any make: