P0159 — O2 Sensor Circuit Slow Response (Bank 2, Sensor 2)
Low severityWhat it means
P0159 is stored when the engine control unit sees a fault involving the downstream oxygen sensor on bank 2 (sensor 2). The bank 2 downstream oxygen sensor sits after that bank's catalytic converter and is used mainly to monitor how well the converter is working. “Slow response” means the oxygen sensor still works but switches between rich and lean too slowly — a classic sign of an aged sensor.
Common symptoms
- Slightly higher fuel use or a failed emissions test
- Often only a check engine light
- A possible failed emissions test
- Rarely any driveability change
Likely causes
- Aged or contaminated oxygen sensor
- Silicone or oil contamination on the sensor tip
- Aged downstream oxygen sensor
- An exhaust leak after the bank 2 converter
What to check first
- Watch the sensor's switching speed in live data and compare with a healthy sensor
- Compare the bank 2 upstream and downstream signals in live data
- Inspect the rear exhaust and the sensor wiring
Can you keep driving?
Generally safe to drive; repair to restore catalyst monitoring and pass emissions.
Frequently asked questions
What is the most common cause of P0159?
The most likely cause is: Aged or contaminated oxygen sensor. Several other faults can set P0159 as well, so confirm the real cause with live data and the checks above before replacing any parts.
Can I just clear P0159 and keep driving?
Clearing P0159 with an OBD2 scanner turns the warning light off, but if the underlying fault has not been repaired the code will usually come back within a few drive cycles. Fix the cause first, then clear the code to confirm the repair worked.
How serious is P0159?
P0159 is a low-severity code. It rarely affects how the car drives, but it is still worth fixing so the engine runs efficiently and passes an emissions test.
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