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P0135 OBD-II Trouble Code: O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)

Check Engine Light

P0135 code definition

O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)

What the P0135 code means

P0135 is the OBD-II generic code indicating the engine control module (ECM) has tested the O2 sensor heater circuit and has detected a problem with the bank 1 sensor 1 O2 sensor heater circuit.

What causes the P0135 code?

  • The ECM tests the O2 sensor heater circuit at first startup for excessive current draw and opens or shorts.

  • The ECM detects a short or open circuit, or an excessive current draw in the heater circuit.

What are the symptoms of the P0135 code?

  • The ECM will not have any O2 sensor feedback until the O2 sensor gives an input.

  • The engine may run rough until the exhaust gets hot enough to activate the O2 sensor to start giving an output voltage.

  • The Check Engine Light will be illuminated indicating a problem.

How does a mechanic diagnose the P0135 code?

  • Visually checks the electrical connections and wire harness to the bank 1 sensor 1 O2 sensor

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

  • Monitors O2 sensor data to see if the heater circuit is working

  • Tests the O2 sensor connector for the proper input voltage from the ECM for the heater circuit

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

  • Follows the manufacturer's specific pinpoint tests for further diagnosis

Common mistakes when diagnosing the P0135 code

  • Not checking the O2 wire harness for water entry into the harness cover
  • Not checking the O2 sensor for oil or other contaminants
  • Not scanning the new O2 sensor to make sure the heater circuit works
  • Replacing parts before conducting thorough pinpoint tests and visual checks

How serious is the P0135 code?

  • O2 sensors are the fuel control feedback the ECM needs to properly control the injectors.

  • The ECM stays in open loop until the O2 system is repaired or the O2 sensor starts working again.

  • The engine stuck in open loop will run extra rich and will burn more fuel and start to build carbon.

What repairs can fix the P0135 code?

Additional comments for consideration regarding the P0135 code

The O2 sensor heater circuit is used to heat the internal parts of the O2 sensor to help it start give feedback to the ECM quicker. If the heater fails, the O2 sensor may still give feedback to the ECM but will take more than the normal time of less than two minutes.

Need help with a P0135 code?

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