Fault code P1135 – a step-by-step guide to diagnosing and fixing it

Error code P1135 is displayed and the check engine light is on - what does this mean?

The DTC P1135 is recognized by the OBD/EOBD system if there is a problem with the heating of the lambda sensor upstream of the catalytic converter (bank 1, sensor 1). This manufacturer-specific trouble code occurs if the heating circuit of the oxygen sensor is not working properly or the heating time takes too long.

What can cause this error code?

• Defective heating of the lambda sensor
• Damaged cable to the lambda sensor
• Corroded or loose plug connections
• Blown fuse in the lambda sensor heater
• Defective engine control unit
• Short circuit in the wiring
• Faulty ground connection of the sensor

What symptoms occur in parallel with fault code P1135?

• Increased fuel consumption: The vehicle requires more fuel than usual because the mixture control is not working optimally.
• Poor engine performance: The engine runs unevenly or has less power, especially when starting cold.
• Black smoke from the exhaust: The unbalanced air/fuel mixture produces visible exhaust fumes.
• Longer warm-up phase: The engine needs more time to reach the optimum operating temperature.
• Jerking when idling: The engine runs unevenly when the vehicle is stationary.

How can the problem with fault code P1135 be rectified?

• Repairing fault code P1135 requires a systematic approach to identifying and eliminating the cause.
• Replace the lambda sensor completely: Replace the defective oxygen sensor upstream of the catalytic converter with a new original part or a high-quality reproduction component to restore proper heating function.
• Repair wiring and plug connections: Check and repair all cables to the lambda sensor, replace damaged cables and clean corroded contacts with contact spray.
• Replace the lambda sensor heater fuse: Locate the relevant fuse in the fuse box and replace it with a new one with the same amperage rating.
• Restore the earth connection: Clean the ground points of the lambda sensor on the engine block and establish a secure electrical connection by using new screws or cleaning the contact surfaces.
• Check engine control unit and replace if necessary: Have the ECU diagnosed by a specialist workshop and, if defective, replace it with a programmed replacement unit.