P0159 on BMW: Causes, Symptoms and Fix Cost

The Quick Answer above is the generic definition. What follows is the model-specific detail for the BMW models that log P0159.

Beyond the generic causes listed on the main P0159 page, these are the patterns noted for BMW models:

Follow these steps to pinpoint the root cause of P0159:

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 and look for companion codes. P0430 or P0156 point to a converter or sensor cluster issue on bank 2; P0139 stored as well means both downstream sensors are slow, which suggests contamination affecting both banks, such as oil or coolant getting into the exhaust
3. Inspect the bank 2 exhaust between the catalytic converter and the downstream sensor for leaks that could distort the gas sample
4. Inspect the Bank 2 Sensor 2 connector and wiring for corrosion, heat damage or partial open circuits
5. Graph both downstream sensor voltages during a steady cruise and then a lift-off fuel cut. A healthy sensor drops toward 0V almost at once when fuel is cut; a sensor that drifts down slowly, or clearly lags the bank 1 downstream sensor, is aged
6. Substitute a known-good sensor. Response time is the only definitive test, so if the new sensor responds correctly, the original was worn out

Estimated repair costs for P0159 in EUR, compiled across makes. Expect BMW parts and labour towards the upper end of each range.

These codes are often seen alongside P0159 or point to related issues, on any make: