O2 Sensor Circuit High Voltage (Bank 2 Sensor 2)
The oxygen sensor on the exhaust after the catalytic converter (Bank 2, Sensor 2) is sending a signal that's too high, like a volume knob stuck at maximum. The ECU expects this sensor to swing between rich and lean readings, but it's stuck in the high zone, preventing proper emission control.
The ECU monitors the voltage output of the post-catalyst oxygen sensor; it should oscillate between 0.1V and 0.9V. When voltage remains consistently above the upper threshold, the ECU detects a fault condition indicating the sensor is not functioning dynamically or the circuit has a short to voltage.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| O2 Sensor Voltage | 0.1V to 0.9V (oscillating) | >0.9V sustained |
| Response Time | <100ms (rich to lean transition) | No switching detected |
Code P0159 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P0159 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.