P0137 Toyota 4Runner
O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2) · Powertrain Code · Medium · Repair: Moderate
What is P0137?
Low voltage from the downstream O2 sensor on bank 1.
When the Toyota 4Runner triggers code P0137 (o2 sensor circuit low voltage (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
- Downstream O2 sensor stuck low voltage — aged or contaminated sensor
- Exhaust leak between catalytic converter and downstream sensor
- O2 sensor wiring shorted to ground
- Water intrusion at downstream O2 sensor connector
Symptoms
- Check Engine Light on
- Slight increase in emissions
- No significant driveability change
- ECM cannot properly monitor catalytic converter efficiency
Notes for Toyota 4Runner
On Toyota trucks and SUVs, the downstream O2 sensor wiring runs along the frame and is prone to damage from road debris — inspect the full run.