P CODES (POWERTRAIN) P0100 - P0199 P0135

    A Comprehensive Guide to Diagnosing and Repairing P0135 Code: Oxygen Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)

    Definition of Trouble Code P0135

    The trouble code P0135 refers to an Oxygen Sensor Heater Circuit Malfunction in Bank 1 Sensor 1. The oxygen sensor monitors the level of unburned oxygen in the exhaust, providing crucial information to the Engine Control Module (ECM). The ECM adjusts the air-fuel mixture for optimal performance and fuel efficiency. The oxygen sensor's heater circuit is responsible for warming the sensor quickly, ensuring accurate readings. This code indicates that the ECM has detected a problem with the heater circuit in the upstream (pre-catalytic converter) oxygen sensor on bank 1 (the side of the engine with cylinder 1).

    How to Diagnose Trouble Code P0135

    Follow these steps to diagnose the P0135 trouble code:

    Step 1: Verify the code
    Connect an OBD-II scanner to the vehicle's diagnostic port and check for the P0135 code. If present, note any other codes that may be related.

    Step 2: Visual inspection
    Inspect the wiring and connections to the oxygen sensor. Look for damaged wires, corroded connectors, or loose connections. Address any issues found.

    Step 3: Test the oxygen sensor heater circuit
    Using a multimeter, measure the resistance of the oxygen sensor heater circuit. Consult the vehicle's repair manual for the specific resistance value expected. If the reading is outside the specified range, the sensor may be faulty.

    Step 4: Test the wiring and connectors
    With the multimeter, perform a continuity test on the wiring between the oxygen sensor and the ECM. Make sure there are no breaks or shorts in the wiring. Additionally, check the connectors for corrosion or damage.

    Step 5: Test the ECM
    If all previous steps show no issues, the ECM itself may be faulty. Consult the vehicle's repair manual for the proper procedure to test the ECM.

    How to Repair Trouble Code P0135

    Follow these steps to repair the P0135 trouble code:

    Step 1: Repair or replace damaged wiring or connectors
    If you found any damaged wiring or connectors during the visual inspection, repair or replace them as needed.

    Step 2: Replace the oxygen sensor
    If the oxygen sensor heater circuit showed a resistance value outside the specified range, replace the sensor. Be sure to use the correct sensor for your vehicle's make and model.

    Step 3: Repair or replace ECM (if necessary)
    If your tests indicate that the ECM is faulty, it may need to be repaired or replaced. This should be done by a professional technician, as it requires specialized knowledge and tools.


    Trouble code P0135 indicates an issue with the oxygen sensor heater circuit in Bank 1 Sensor 1. Properly diagnosing and repairing this issue will ensure optimal engine performance and fuel efficiency. Follow the steps above to diagnose and repair the problem, and consult your vehicle's repair manual for specific information regarding your make and model.

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