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P0136 OBD-II Trouble Code: O2 Sensor Circuit Malfunction (Bank 1, Sensor 2)

Check Engine Light

P0136 code definition

O2 Sensor Circuit Malfunction (Bank 1, Sensor 2)

What the P0136 code means

P0136 is the OBD-II generic code indicating the downstream O2 sensor for bank 1 fails to meet the minimum and maximum voltage limits calibrated for the ECM to see.

What causes the P0136 code?

  • The ECM monitors the O2 sensor’s highest and lowest voltages. This code occurs when the voltage limits are not within specifications programmed into the ECM.

  • The ECM detects a voltage problem and turns on the Check Engine Light.

  • The ECM uses other O2 sensors to try and control the fuel injection with known values.

  • There is an exhaust leak or catalyst failure in front of the sensor.

What are the symptoms of the P0136 code?

  • The engine may run excessively rich if the engine goes into open loop.

  • The engine may start to misfire if the spark plugs get fouled out over time.

  • The Check Engine Light will be illuminated.

  • You may have exhaust leaks or loss of power from a clogged or bad catalyst.

How does a mechanic diagnose the P0136 code?

  • Scans codes and documents freeze frame data then clear codes to verify failure

  • Monitors O2 sensor data to see if the voltage is switching back and forth between low and high at a fast rate compared to other sensors

  • Checks the O2 sensor wiring and the harness connections for any corrosion

  • Checks the O2 sensor heater circuit for the proper resistance to specifications

  • Checks for exhaust leaks before the sensor

  • Follow the manufacturer's specific pinpoint tests for further diagnosis.

Common mistakes when diagnosing the P0136 code

Follow these simple guidelines to prevent misdiagnosis:

  • Repair any exhaust leaks before the sensor to prevent incorrect readings.

  • Check the O2 sensor for oil or coolant contaminants from engine leaks.

  • Repair any harness that is damaged properly without taking shortcuts to prevent repeat failures.

  • Check the removed O2 sensor for damage from a defective catalyst and replace the catalyst if it is faulty.

How serious is the P0136 code?

  • The voltage output from the O2 sensor may point to engine and exhaust problems causing the O2 sensors to give erratic output voltages.

  • The O2 sensor may not read correct if the catalyst is damaged in front of the sensor.

  • The ECM may stay in open loop until the O2 system is repaired or the O2 sensor starts working again causing extended rich conditions that could possibly damage other engine components.

What repairs can fix the P0136 code?

Additional comments for consideration regarding the P0136 code

The O2 sensor circuit for bank 1 sensor 2 is used to give a voltage feedback to the ECM to control the fuel and provide information about catalyst operation.

Need help with a P0136 code?

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