Fault code P0418 – a step-by-step guide to diagnosing and fixing it

Error code P0418 is displayed and the check engine light is on - what does this mean?

The DTC P0418 is recognized by the OBD system if there is a problem with the secondary air system relay A (control circuit). This fault code indicates a malfunction in the electrical control circuit of the secondary air pump relay. For various manufacturers, this trouble code may also be referred to as "Secondary Air Injection System Relay A Control Circuit".

What causes can this fault code have?

• Defective secondary air system relay
• Damaged wiring to the relay
• Corroded or loose plug connections
• Defective secondary air pump
• Faulty engine control unit (ECM/PCM)
• Blown fuse in the secondary air circuit
• Oxidized relay contacts
• Short circuit in the relay coil

What symptoms occur in parallel with fault code P0418?

• Starting problems: The vehicle is more difficult to start when the engine is cold
• Increased emissions: Poorer exhaust emissions, especially when starting cold
• Uneven engine running: Engine runs unevenly during the warm-up phase
• Check engine light: Permanent display of the check engine light
• Loss of power: Reduced engine power during the first few minutes after starting
• Increased fuel consumption: Particularly noticeable on short journeys

How can the problem with error code P0418 be rectified?

• Repairing EOBD error code P0418 requires a systematic diagnosis of the secondary air circuit.
• Replace the defective secondary air system relay with a new original part and check the function
• Repair or replace damaged cable connections between ECM and relay, including ground connections
• Clean all plug connections with contact spray and ensure tight connections
• Replace the defective secondary air pump if it overloads or blocks the relay
• Program or replace the engine control unit if there are internal defects
• Replace blown fuses and check the entire circuit for short circuits