Fuse 15

[kevc]

Does the fuse have to go back in to pass an MOT (just thinking of emissions tests)?

[Kev]

The valve doesn't have anything to do with exhaust gases, only the noise

[Thunder Dump]

My post was more to point out that at idle (and only at idle), in any mode if the active exhaust light is on (switch is active) then the valves will be open. Depending on mode, as soon as the revs move off idle the valves will close.

That's where we differ - in my car at idle if the switch is lit and I'm not in dynamic mode the valves remain closed until I get to 1500 rpm. Only in dynamic mode are my valves open at idle (and all time, of course). So your statement may be true for your car, but it's not a fact for all, so shouldn't be represented as such.

Fair enough. My scenario is accurate for the '21+ V8s with the electronic valves.

[Kev]

Well, I’m glad we’ve got to the bottom of what Fuse 15 does, although I’m surprised no one has mentioned Fuse 43 on the early model years as that’s denoted as ‘Active Exhaust’? I’ll get my popcorn…

[Lunar]

Oh no! - you mentioned Fuse 43 - best make that a large popcorn.
Then we can move on to pump or manifold vacuum
I wonder if you could just use a length of washer pipe and suck on it at will

[Andrew24]

Hi Matt

Does this leave the valves open all the time, with this fuse removed?

[scm]

Hi Matt

Does this leave the valves open all the time, with this fuse removed?

It does on the earlier models but I think from posts I've seen here and on the US forum that the latest facelift is a bit different in that it "remembers" the valve state and preserves it if you remove the fuse, so if the valves are open when you remove the fuse they stay open but if they were closed they'll stay closed. Maybe someone with the latest facelift can confirm (or deny!) this behaviour.

[Andrew24]

is it any different compared to having the active exhaust button on and in dynamic mode? I suppose it changes depending on RPM.

[Deleted User 4828]

Hi Matt

Does this leave the valves open all the time, with this fuse removed?

It does on the earlier models but I think from posts I've seen here and on the US forum that the latest facelift is a bit different in that it "remembers" the valve state and preserves it if you remove the fuse, so if the valves are open when you remove the fuse they stay open but if they were closed they'll stay closed. Maybe someone with the latest facelift can confirm (or deny!) this behaviour.

My thinking is that if you remove the fuse the valves will stay in the position upon removal, as this fuse powers the mechanism, so irrespective if the control signal to open or close is given, it will not activate, I need to look further into mine, I think the exhaust valves are open all the time. I need to remove the fusebox to ensure the cabling is in situ also. I need to get them to work fully before removing the fuse etc but need to get back to normal to make it an option.

[scm]

is it any different compared to having the active exhaust button on and in dynamic mode? I suppose it changes depending on RPM.

The valves are controlled by the car, but if you remove fuse 15 that module can no longer do its stuff, so the valves will always be fully open (subject to my previous post regarding the latest facelifts models).