BSM B3 teardown - what is inside the BSM module

The C3 BSM module is the engine bay fuse box and this sits next to the battery and covers the hidden maxi fusebox.

If you want to remove the BSM module then follow these BSM removal instructions


With the BSM removed the fuses can be easily removed with a pair of needle nosed pliers and the fuse legs should be inspected for corrosion.


Inside the BSM is a circuit board with relays


The underside of the BSM is coated with a clear varnish and contains no components


and there is a computer daughterboard that takes CAN/VAN signals from the BSI and Engine ECU for the relays to act on.


These BSM units are still quite common, you can pick up a replacement here, on eBay, quite cheaply here. No reprogramming needed, straight swap for a like for like BSM module.

But if they get rare or expensive then the relays are probably going to be of the most interest for replacement

Get the 51ND10-W1 here


Get the 512ND10-W1


and you can get the V230676-A3001-D142 here

The 3 big relays marked 'V230676-A3001-D142' are labelled A, B and C in the diagram

The function of Relay A is the 'double injection relay' that's the main power relay to the whole BSM. If this relay is not energised, there is no power to the BSM module.

Relay B is the heater blower motor control and is associated with fuse F18 (40A)

Relay C is for the Power Steering and Engine ECU. The associated fuse is F8 (20A)