Mercedes A Klasse Ignition Problem

I had a similar issue with my A Klasse. The Terminal 15 error suggests a power supply problem to the ignition system. Did you check the fuses related to the engine control unit (ECU) and ignition system specifically? Sometimes, a fuse can appear intact but still be faulty. Inspect the wiring harness near the ignition switch for damage or corrosion. Has the mechanic inspected the relay switch?

I examined the fuses, but not specifically those for the ECU or ignition system. Could you clarify the location of those fuses and relays? What visual indicators of damage or corrosion should I look for in the wiring harness?

Fuse locations can vary, but the diagram should be inside the fuse box cover. Look for fuses labeled 'Engine Control Unit,' 'Ignition,' or similar. For the wiring harness, check for cracked or frayed wires, loose connectors, or green/white powdery residue, which indicates corrosion. Given the complexity, I'd advise having a professional mechanic further diagnose the issue. It's likely a defective wire or connection, and the mechanic will be able to pinpoint it exactly.

I've entrusted my Mercedes to a mechanic. The diagnosis confirmed a defective wire, specifically a corroded connection within the ignition circuit. The component has been replaced, and the vehicle now functions perfectly. Thank you for sharing your expertise and preventing a potentially misguided troubleshooting effort.