Is the k40 relay linked to the supercharger clutch?

I ask as the clutch is not engaging so no kompressor boost. I had the dreaded K40 relay fail in September and the car was off the road for 23 days as various garages tried to resolve the fault (the car wouldn't start). Eventually I replaced the K40 unit with a second hand one from Ebay and the car started straight away.

Now I don't do a lot of open highway miles but I've realised that the Supercharger has stopped working and I think it all stems back to the original breakdown, is there anything I can do before I have to throw more money at a garage to look at it?

I appreciate your help. Jim.

What year car?

At some point you will get a check engine light if the super charger isn't engaging. After a cold start the SC runs to provide air injected into the exhaust to assist in heating up the catalytic converters. After the engine warms up, car comes to a stop and is idling for 5 ish sections, it engages again to test oxygen sensor function.


As for K40 relay, is this the long thin box with 5 or so small fuses and one large fuse? On non SC cars in the late 90's, the large fuse runs the electrically driven emissions air pump. For a SC car I'm not sure where the clutch signal comes from. Try to gain access to a wiring diagram and I can have a look.