(If your ME20 has different connector sizes/numbering, map pins by function using continuity to known harness points.)

| Pin | Function | Verified Status | |------|-------------------------------|------------------| | A1 | Main relay control (output) | ✅ Verified | | A2 | Battery voltage (permanent) | ✅ Verified | | A3 | Ignition switch input | ✅ Verified | | A4 | Sensor ground (ECU reference) | ✅ Verified | | A5 | Engine ground (power stage) | ✅ Verified | | A18 | Crankshaft position sensor (+) | ✅ Verified | | A19 | Crankshaft position sensor (-) | ✅ Verified | | A32 | Camshaft position sensor signal | ✅ Verified | | A33 | Throttle position sensor (wiper) | ✅ Verified | | A40 | Knock sensor 1 | ✅ Verified | | A41 | Knock sensor 2 | ✅ Verified | | A54 | CAN High (diagnostics/immobilizer) | ✅ Verified | | A55 | CAN Low | ✅ Verified |

If your diagnostic scanner cannot communicate with the ECU while it is inside the vehicle, use a multimeter to check for voltage drops across and the negative battery post. Bosch ME20 units are highly sensitive to weak ground paths, which can mimic a completely dead or "bricked" ECU.

Often a pink/green or similar wire that triggers the pump when the ECU sees a crank signal. Starter Circuit:

If you cannot establish communication with the ECU on the bench, systematically check these variables:

To provide you with a specific wiring diagram or a deeper dive into a particular function, could you let me know: What are you working on?

Verified pinout from Mercedes-Benz diagnostic documentation.

Throttle Position Sensor (TPS) Sensor Reference Voltage (+5V) Pin 48: Front Oxygen Sensor (Lambda) Signal 4. Actuator Outputs (Drivers)