What it means
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.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bank 2 sensor 2 sits after the catalytic converter and monitors the exhaust leaving that converter; its signal also helps the ECU assess catalyst operation. P0156 sets when the ECU detects an electrical or signal problem in this downstream sensor circuit, so it may be unable to run the bank 2 catalyst monitor.
Common causes
Most likely first.
- Oxygen sensor aged or failed
- Sensor wiring open, shorted, or damaged
- Loose or corroded connector
- Exhaust leak near the sensor
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
How to diagnose it
- Record freeze-frame data and inspect live data for bank 2 sensor 2, comparing it with bank 1 sensor 2 when the engine and catalyst are warm.
- Inspect the downstream bank 2 sensor connector and wiring along the exhaust for corrosion, loose pins, melted insulation, or impact damage.
- Check for an exhaust leak around the sensor or its bung that could affect the reading.
- Test the sensor signal circuit for opens or shorts and check its connector terminals using the wiring diagram and manufacturer’s specification.
- If the circuit and exhaust are sound, assess bank 2 sensor 2 response with a scan tool before replacing it.
Common fixes
- Repair an exhaust leak near bank 2 sensor 2.
- Secure or clean the downstream sensor connector.
- Repair wiring damaged by heat, rubbing, or impact.
- Replace bank 2 sensor 2 if its signal remains faulty after circuit checks.
Can I keep driving?
A steady check-engine light generally permits a short drive, but the bank 2 catalyst monitor may not complete and emissions testing can fail. Get it checked soon, especially if fuel use or engine running worsens.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.