Emissions

P0136 — Post-Catalyst Oxygen Sensor Circuit Malfunction (Bank 1 Sensor 2)

Severity: low Safe to drive

What P0136 means

P0136 means the engine computer sees an incorrect or missing signal in the circuit of the downstream oxygen sensor (Bank 1, Sensor 2), located after the catalytic converter. This sensor normally gives a fairly steady signal that helps the PCM judge catalyst efficiency. When the signal is out of range or stuck, the PCM sets the code and turns on the check engine light.

Symptoms

  • Check engine light on
  • Slightly worse fuel economy
  • Occasionally a rough idle
  • Failed emissions test
  • May appear alongside P0420/P0430

Possible causes

  1. Failed Bank 1 downstream oxygen sensor
  2. Damaged, corroded or chafed sensor wiring or connector
  3. Failed sensor heater circuit
  4. Exhaust leak near the sensor
  5. Faulty or contaminated catalytic converter skewing the signal
  6. Rarely, a PCM fault

How to diagnose

  1. Scan for codes and review freeze-frame data and other DTCs
  2. Inspect the sensor harness and connector for damage, corrosion or heat melting
  3. Look for exhaust leaks upstream of and near the sensor
  4. Watch live sensor data on a scan tool for voltage and response
  5. Test heater circuit power and resistance per the wiring diagram
  6. Check ground and reference voltage at the connector
  7. Review fuel trims and catalyst condition
  8. If wiring is good, replace the sensor and clear the code

Common fixes

  • Replace the Bank 1 Sensor 2 oxygen sensor
  • Repair the wiring or connector
  • Fix the exhaust leak
  • Replace the catalytic converter if it is the cause
  • Rarely, diagnose or replace the PCM

P0136 on different brands

Ford · manuals
On some newer Ford gasoline engines the code can appear with an extension such as P0136:12, which identifies the specific detected condition, here a circuit shorted to battery voltage.

Questions and answers

Can I drive with a P0136 code?

Usually yes, as it rarely harms the engine. The light will stay on though, and fuel economy and emissions inspection results may suffer, so don't put the repair off for long.

Do I always need a new sensor for P0136?

No. Check the wiring, connector and exhaust leaks first. Replace the sensor only when the circuit is sound and the sensor signal or heater is out of spec.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.