E39 540i relays?

[njw1]

Does any knowledgeable person know what this relay is for and why has it decided to catch fire!?







I started the car (MY2000 e39 540i) and within a minute the cab had completely filled with smoke which seemed to be coming from behind the dash, I quickly disconnected the battery and had a poke about but couldn't see anything obvious, I then reconnected the battery and had no more smoke but did notice that the abs and t/c lights are staying lit with the ignition switched on whereas they usually go off after a few seconds, I tried starting it and it turned over and coughed and spluttered but wouldn't fire as if it was out of petrol. I then remembered about the compartment underneath the n/s pollen filter and whipped the lid off to reveal the above and below;







So, does anyone know what this relay is actually for and why it has decided to self destruct? Thanks in advance.

[helix402]

Google suggests it’s K6304 auxiliary air pump relay. I know on the M52tu the entire aux air pump system can be binned and no DME will light comes on. Maybe an option if the relay is what Google suggests.

[njw1]

helix402 said:

Google suggests it’s K6304 auxiliary air pump relay. I know on the M52tu the entire aux air pump system can be binned and no DME will light comes on. Maybe an option if the relay is what Google suggests.

Thanks, as you say, it is indeed for the aux air pump, upon inspection of the pump with a multimeter it was reading a dead short, the main fuse for pump (fuse #107 50A) in the hidden fuse box under the drivers seat had also blown but obviously not quickly enough hence the smoke and fire! Regarding the ABS and T/C lights remaining lit and the lack of engine starting I found that fuse #31 (10A) in the glovebox had also blown, this fuse (as you may have guessed!) is for the control signal to both the ABS and fuel pump relays, I assume the wiring on the secondary air pump relay shorting out caused it to blow.
It seems that the the secondary air system on the M62 engine can also be removed entirely without triggering the engine warning light (but will still log a code) so I've tidied up and heatshrunk the damaged wiring and left the pump disconnected for the time being and the car seems to be running perfectly (touches wood!).

[helix402]

Good news. The aux air pump is just to increase cat effectiveness from cold, it won’t affect the running.