What it means
The ECU detects that the downstream oxygen sensor on bank 2 responds too slowly.
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 monitors oxygen in the exhaust after the bank 2 catalytic converter. P0159 sets when the ECU detects that this downstream sensor responds too slowly to changing exhaust conditions, which can prevent reliable catalyst monitoring.
Common causes
Most likely first.
- Rich condition on bank 2
- Signal wire shorted to voltage
- Connector pins corroded - high contact resistance
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 use warm live data to compare the response of bank 2 sensor 2 with bank 1 sensor 2 under similar operating conditions.
- Inspect the downstream bank 2 sensor connector and wiring for corrosion, poor terminal contact, heat damage, or a signal wire shorted to voltage.
- Check for an exhaust leak near bank 2 sensor 2 and review bank 2 fuel trims and misfire data for conditions that could distort sensor response.
- Test the signal circuit and sensor response using the vehicle wiring diagram and manufacturer’s specification.
- If the exhaust and wiring are sound, replace bank 2 sensor 2 only after confirming that its response is persistently slow.
Common fixes
- Repair poor connector contact or damaged downstream sensor wiring.
- Fix an exhaust leak near bank 2 sensor 2.
- Correct a confirmed rich-running or misfire condition affecting bank 2.
- Replace bank 2 sensor 2 if it responds slowly despite a sound circuit and normal engine operation.
Can I keep driving?
A steady light usually allows a short, careful drive, but the ECU may not complete the bank 2 catalyst monitor and emissions can increase. Avoid continued driving if the engine runs poorly or the warning light flashes.
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.