P0137 moderate

O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2)

What does P0137 mean?

The P0137 code means the vehicle's onboard diagnostic system has detected: O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2). This is a moderate severity code.

Common Symptoms

  • Check Engine Light on
  • Engine may run lean
  • False lean trim readings
  • Possible P0171 combination

Probable Causes (Ranked by Likelihood)

  • O2 sensor stuck lean (low voltage output) Very High
  • Exhaust leak pulling in fresh air near sensor High
  • Short to ground in signal wire Moderate
  • Genuine lean running condition Moderate

Step-by-Step Diagnostic Procedure

  1. Check downstream O2 voltage. Stuck below 0.2V consistently indicates lean bias or a circuit fault.

  2. Inspect exhaust system for leaks between the catalyst and the sensor.

  3. Check signal wiring for ground shorts.

  4. If fuel trims are also lean (positive values), investigate the underlying lean condition first.

Frequently Asked Questions

Can an exhaust leak after the catalytic converter cause P0137?

Yes. Fresh air pulled into a small exhaust leak dilutes the exhaust gases near the sensor, causing a lean (low voltage) reading that is not representative of actual catalytic converter function.

Explore More Codes

All codes | Browse by vehicle make