I had some difficulties with my E430 (W210) 1999.
When I tried starting the car the engine was not turning over. In fact nothing happened at all, except some kind of "humming noise" and the lights in the instruments came on. I could leave
it for a while and try again and it would start and runs like it should. After that it could start maybe 5 or 6 times and then fail again.
- Battery was fully charged
- I changed CPS (Kurbelwellensensor)
- I changed K40 relay unit (A 000 540 00 72)
- Removed and checked the ignition switch
The relay K40 (A 000 540 00 72) unit (yellow circle) was not closing when it had the starting issue. When it was starting, the relay was closing as well.
The fault was found in the ECU. It had a bad soldering point at the EEPROM (yellow circle).
ECU: Mercedes number: A 026 545 69 32. Bosch number: 0 261 206 303. The same ECU is used in other Mercedes, 8 cylinders as well. For ex. ML 430.
In case of replacing an ECU you have to keep in mind that the door lock (driver side), ignition switch and the ECU has to be paired together. It means, copying immobilizer data from the old ECU to the new one.