Complicated Headlight Failure - 2000 V40

[Mike Brown]

I, like many others, have been plagued by frequent failures but always felt as though that was a small price to pay with over 170k miles.

However, this time my problem is different, and changing the bulb didn't make any difference at all. A meter check of the bulb and fuse (the right and left lamps are on a seperate fuse) show that both are good (I swapped them with others as well to verify this), and there is voltage at the harness to the bulb and the assembly. I then removed the assembly and attached it to the drivers side and everything works fine, but when swapping the drivers side to the passengers the problem persisted. It almost seems as though when the circuit begins to draw it shorts out.

Electrical gremilins are admittedly my weakness, and the european Haynes manual for this car isn't very helpful. The diagram shows a relay, but after searching through the engine compartment and hanging upside down and removing the relays on the drivers side I still can't seem to find one.

I did find an interesting wiring splice that appears to have been done by the dealer (service tag is still attached) wherein two smaller gauge wires come from the ECU and attach via a connector before rejoining the rest of the wires in the loom. When I jump the connector terminal from the drivers side to the passenger side everything lights up as it should prompting me to believe my problem is the ECU. However, before swallowing that pill I wanted to ask here if anyone has seen or heard of this before? Am I missing something?

For what it is worth, it seems the computer (30859699) is the same used in the s80 in 2000, whose electrical problems are well documented.

[Mike Brown]

I wanted to provide an update in case anyone else experiences a similar issue.

My problem (no passenger side headlight, bulb and fuses are good, voltage was present) was traced back to the Central Electronic Module. The unit is stamped 38859699 and is located behind the driver