Fault code P0137 – a step-by-step guide to diagnosing and fixing it

Error code P0137 is displayed and the check engine light is on - what does this mean?

With this DTC, the OBD/EOBD system detects that the voltage of the lambda sensor in bank 1, sensor 2 (downstream O2 sensor) is too low. This trouble code affects the exhaust gas purification system and catalytic converter monitoring. This fault code can be interpreted slightly differently by different manufacturers, but always refers to the downstream oxygen sensor.

What causes can this fault code have?

• Defective downstream lambda sensor (bank 1, sensor 2)
• Damaged or corroded wiring to the O2 sensor
• Loose or dirty plug connections
• Defective catalytic converter with reduced efficiency
• Exhaust gas leakage upstream of the downstream sensor
• Faulty engine control unit software
• Short circuit in the sensor heater
• Dirty or sooty lambda sensor

What symptoms occur in parallel with fault code P0137?

• Increased fuel consumption: The vehicle consumes more fuel than usual due to the faulty mixture control.
• Poor exhaust emission values: Increased emission values are measured during the exhaust emission test.
• Unsteady idling: The engine runs unevenly or rough at idle.
• Loss of power: Reduced engine power, particularly noticeable at higher engine speeds.
• Check engine light: The check engine light lights up continuously or flashes.

How can the problem with error code P0137 be rectified?

• The repair requires a systematic diagnosis to identify the exact cause.
• Replace the lambda sensor: Replace the defective downstream O2 sensor in bank 1, position 2 with a new one, observing the correct tightening torques.
• Repair wiring: Locate damaged cables to the lambda sensor, repair severed cables or replace the complete cable set.
• Clean plug connections: Clean all plug contacts to the oxygen sensor, treat with contact spray and seal tightly.
• Replace the catalytic converter: If the catalytic converter is defective, replace it with a new one and then carry out a test drive to check its function.
• Seal exhaust leaks: Locate leaks in the exhaust system upstream of the sensor and seal them with suitable repair pastes or by welding.
• Carry out a software update: Have the engine control unit programmed with the latest firmware from the vehicle manufacturer.