Gremlins....

[KiwipugUK]

I have a wee problem with the 406. I thought the front fogs weren't working because they were filled with water and the plugs corroded so I replaced them with new units. Still no go... Can't find any relays anywhere and there are no fuses out that I can see. What gives??
Also, have tried 4 different sensors in the mirror but it still shows 50 something degrees. Do I need to reset something?

[steve_earwig]

Check fuse 6 in the engine fuse panel (and then check the rest of them ). The foglights are mux (relay 11) so there's always the possibility the car doesn't know it has them...

Dunno about the temp sender, it's not set to Fahrenheit is it?

[KiwipugUK]

Ok I'll have look at fuse 6, if I turn the knob at the end of the stalk the light comes on to say the fogs are on. Would I still do this if they weren't programed?
Temp display still says c after the number so I reckon it's in centigrade.

[steve_earwig]

Then it probably does know. Ah well, check the fuse and see if there's any voltage on it - the relay is after the fuse so it should have a permanent 12 volts. Unfortunately the relays do break...

What does it read without the sensor? I can't remember if the resistance goes down with heat like you'd expect or if they go up, a bad connection would introduce some extra resistance but I'd expect it to go down, not up...

[KiwipugUK]

Still waiting for a spare minute to check the fuses. Are we taking the box under the bonnet or under the dash? There are only 2 relays under the dash tho that i noticed the other day when i was looking around.
Display reads "--c" when sensor is not conected. I know they are common fault, but is it possible that all 4 are just faulty? I even got one of the off a Citroen C5, just in case!

[steve_earwig]

Are we taking the box under the bonnet or under the dash?

engine fuse panel

I've no experience of the temperature sensors I'm afraid, but 4 dodgy ones does seem a bit unlikely. I wonder if... Nah, D8's and D9's are the same. C5's are all different though.