Fault code P0139 – a step-by-step guide to diagnosing and fixing it

Error code P0139 is displayed and the check engine light is on - what does this mean?

The OBD/EOBD system has detected that the rear lambda sensor (bank 1, sensor 2) is reacting too slowly to changes in the oxygen content. This DTC P0139 concerns the lambda sensor after the catalytic converter and can occur with different manufacturers with slightly different descriptions.

What causes can this error code have?

• Defective rear lambda sensor
• Dirty or defective catalytic converter
• Damaged cables or plug connections to the lambda sensor
• Corroded or loose plug connections
• Defective engine control unit (ECU)
• Vacuum leak in the intake system
• Dirty air filter
• Defective fuel injectors
• Faulty spark plugs or ignition coils

What symptoms occur in parallel with fault code P0139?

• Increased fuel consumption: The vehicle consumes more fuel than usual
• Poor engine performance: Reduced acceleration and loss of power
• Uneven idling: The engine runs unevenly at idle
• Exhaust odor: Noticeable smell from the exhaust
• Misfiring: The engine stutters or jerks when driving
• Black smoke: Dark exhaust fumes from the exhaust pipe

How to fix the problem of error code P0139?

• The repair requires a systematic diagnosis to identify the exact cause:
• Replacement of the rear lambda sensor (bank 1, sensor 2) after checking the electrical values and response time
• Repair or replacement of damaged cables and plug connections to the lambda sensor with subsequent function test
• Cleaning or replacement of the catalytic converter if soiling or a defect is detected
• Elimination of vacuum leaks in the intake system by replacing defective hoses or seals
• Replacing the air filter and cleaning the intake tract in the event of heavy soiling
• Repairing the engine control unit or updating the software after a thorough electronic diagnosis