This may be common knowledge, and I could just be the last to find out about it, but I can't find any reference to it in the search system... I apologize if this is all well known.

The workshop manual BEM test procedure (on 5p3118.pdf p16 - Chassis electrical/Base/Basic test mode (BTM) procedure) would give one the impression that this procedure requires a MUT service tool.

This is not the case. As for the fault codes, a jumper connected between pins 1 and 4 of the OBDC enables the test. (The MUT must make this connection also, but is not needed, just the jumper)

Instead of turning on the ignition, you operate the high beam switch for a moment, with the driver's door open. If the interior light was on because of the open door, it goes out, indicating the test mode is active. The security lamp on the dash comes on also, and displays some flash codes.

The cool part is that each time the high beam is pulsed, different actions occur with actuators controlled by the BEM. Things such as the horn, door locks and lighting can be activated this way.

Remove the jumper to exit the procedure.

The manual is a little sketchy on how to use this fully, so close reading a bit of experimentation and is required.

(I don't know how this works, as I can't find any connection from OBDC pin 1 to the BEM in the circuit diagrams.)

Hoping this is of interest to some...