P0136 Toyota 4Runner
O2 Sensor Circuit Malfunction (Bank 1, Sensor 2) · Powertrain Code · Medium · Repair: Moderate
What is P0136?
The downstream (post-catalytic converter) O2 sensor on bank 1 is malfunctioning.
When the Toyota 4Runner triggers code P0136 (o2 sensor circuit malfunction (bank 1, sensor 2)), it typically points to an issue in the powertrain system. Below you'll find the most common causes, symptoms, and repair options specific to the Toyota 4Runner.
This repair is rated moderate, meaning some experience and specialty tools required.
Diagnostic data on this page is compiled from publicly available repair resources and technical service bulletins. Always have a qualified mechanic confirm the diagnosis before authorizing repairs on your Toyota 4Runner.
Common Causes on Toyota 4Runner
- Bank 1 Sensor 2 (downstream) O2 sensor malfunction
- Downstream O2 sensor contaminated by oil burning past worn piston rings
- Damaged wiring from road debris or exhaust heat
- Failing catalytic converter causing abnormal downstream O2 readings
Symptoms
- Check Engine Light on
- May not pass emissions readiness monitors
- No significant driveability symptoms
- Possible slight decrease in fuel economy
Notes for Toyota 4Runner
If P0136 appears alongside P0420 or P0430, the catalytic converter is the likely root cause — replace the cat before the downstream O2 sensor.