Tanker01

My '03 C230 Coupe doesnt engage the ignition anymore. Battery tests good, radio works, doors lock/unlock, everything works like normal EXCEPT the ignition doesnt engage and let me turn the car on. Only thing recently done in the last year is I changed the starter a week and a half ago. I took it driving last night and it started like normal when leaving the house. I drove it to where I was going and when we went to leave it took about 5 tries to get the ignition to engage and let me turn the key. This morning when I went to drive it, absolutely nothing happens now. I checked all fuses on all 3 fuse boxes and none are blown. The key battery tests at 6v as it should so it isnt dead either. Is my ignition itself dead maybe? What is the best way to troubleshoot this?

Currently I disconnected the battery to see if I can get the ECU to reset or something to see if that might help. I can not scan for codes as I can not turn the key at all.

Plutoe

you may repeat may have a K40 relay in the starting electrical system---the only way to confirm is get a scan or search WIS with your VIN and review the starting circuit---if you dont understand this dont quit your day job run to a mechanic

Tanker01

What does this K40 relay do, where is it located, and what is its mode of failure? Is it one of the relays in the engine bay or back in the boot? Is there a relay that disables the steering lock or is the K40 what does that? Insults to my competence aren't necessary, I'm actually a little overqualified to be working on this car I just am not super familiar with German vehicles I drive Fords mostly otherwise which don't have stupidly overdesigned IR optical ignition systems that can fail 17 different ways.... This is just my Fathers daily driver.

Also worth noting I already disassembled the key and cleaned the optical senders and verified the little window is clean.