P0136 moderate

O2 Sensor Circuit Malfunction (Bank 1, Sensor 2)

What does P0136 mean?

The P0136 code means the vehicle's onboard diagnostic system has detected: O2 Sensor Circuit Malfunction (Bank 1, Sensor 2). This is a moderate severity code.

Common Symptoms

  • Check Engine Light on
  • Emissions test failure
  • Possible false P0420 trigger
  • Slight fuel economy change

Probable Causes (Ranked by Likelihood)

  • Failed downstream O2 sensor Very High
  • Wiring damage or connector corrosion High
  • Sensor heater failure Moderate
  • Exhaust leak near downstream sensor Low

Step-by-Step Diagnostic Procedure

  1. Monitor Bank 1 Sensor 2 voltage. At steady highway speed it should show a slow, mostly steady signal around 0.6-0.7V.

  2. If signal is erratic or shows no voltage, check wiring and connector.

  3. Test heater circuit resistance.

  4. Replace sensor if confirmed faulty.

Frequently Asked Questions

Will a bad downstream O2 sensor cause P0420?

Yes. A lazy or slow downstream sensor mimics the waveform signature of a failed catalytic converter. Always replace or test the downstream sensor before buying a catalytic converter.

Explore More Codes

All codes | Browse by vehicle make