P0136Powertrain
Powertrain · SAE
O2 sensor circuit (bank 1, sensor 2)
Meaning
The control unit detects a fault in the downstream (post-catalyst) oxygen sensor circuit on bank 1. This sensor monitors how well the catalytic converter is working.
Common causes
- Worn-out or failed downstream oxygen sensor
- Damaged or corroded sensor wiring or connector
- Exhaust leak near the sensor
- Sensor contamination (oil, coolant or silicone residue)
- Incorrect sensor ground or supply
- Pin or connection fault on the control unit side
Symptoms
- Check-engine light on
- Possible slight increase in fuel consumption
- Engine generally runs smoothly
- Failed emissions test
- Catalyst monitor not completing
Severity
Moderate: driving is not affected, but the system can no longer verify catalytic converter efficiency and the car would fail an emissions test.
What to do
- Read the downstream sensor live data and compare it with the upstream sensor
- Inspect the sensor wiring, connector and ground for damage or corrosion
- Check for an exhaust leak near the sensor
- If the circuit is sound, replace the downstream oxygen sensor and clear the code to verify