P0156
O2 Sensor Circuit Malfunction (Bank 2, Sensor 2)
Same condition as P0136 but on the downstream sensor of bank 2. The catalyst efficiency monitor for bank 2 cannot run while this fault is active.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: easy
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
Common causes
Ordered by how often each turns out to be the cause.
- Downstream sensor agedCommon
Parts involved
- Oxygen Sensor Downstream
P0156 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.