[s-cars] S6 starting problem - ECU fuse

[Steve Eiche]

Rich,
Unless it got struck by lightning, you won't likely see any obvious damage.  

As Feico has mentioned, we have both repaired a few ECUs with this problem.  What happens is that a (sacrificial in this case) protection diode protection diode on the battery voltage supply for the ECU shorts out (goes to a low resistance state) due to an overvoltage condition.  This can result from voltage spikes from jumping a battery, bad connections at the battery, etc.  If you have a multi-meter, check the large diodes near the connector.  One of them will be shorted.  From memory, I think that it will be D452 (?), which is a BZY27 I believe (don't quote me). You may have to desolder and lift one end to verify that you are reading only that component.

In any case, it is a relatively simple fix.   

Steve Eiche 

opening the ECU and looking for damage sounds like the next
logical step. i can have that on the workbench in a couple of
minutes. thanks mark.

rich