Heated rear window switch problem

I have been trying to get my HRW switch to work over the last couple of days.

When the switch is pressed I get nothing happening and no light on on the switch. Thought it might be the round relay on the fuse board below the steering wheel, so borrowed a known working one and that made no difference.

I then thought it might be the switch, so tried the cruise control switch with the ignition on - no joy - BUT when I plugged the HRW switch back in it was working Turned off the ignition and turned it on again, pressed the switch and nothing. Did the cruise control switch thing again and it worked, but as soon as the ignition is turned off it won't work again

Any ideas as to what might be wrong, as electrics are not my strong point??

You have started the basic diagnostics by swapping out parts, just need to take it further

Have you checked MFU operation?

RAVE instructions
Multi–Function Unit (MFU)
The multi–function unit (MFU) is mounted on the
rear of the passenger compartment fusebox and has
an input to operation of the following:
Heated rear screen
Heated front screen
Courtesy lights
Side and headlights
Rear fog guard lamps
Headlamp power wash
Front wipers
Rear wash/wipe
Diagnostic Procedure
1. Close all doors and the tailgate.
NOTE: If the oil pressure switch goes open circuit
(engine is started) during the following procedure,
the MFU will exit the diagnostic mode immediately.
2. Press and hold the heated rear screen switch
and switch on the ignition.
3. Release the heated rear screen switch within 2
seconds and the MFU will beep to indicate that it’s in
diagnostic mode 1.
4. Press the heated rear screen switch; the MFU
will beep twice. In turn, operate each of the following
switches, heated front screen, rear fog guard lamps,
side lights, headlights, front wiper, and rear wiper.
The MFU will beep twice each time a switch is oper-ated.
5. Pressing the heated rear screen again will cause
the MFU to enter diagnostic mode 2.
6. The MFU will provide outputs to the following in
order given below:
Heated rear screen relay energised for 2 seconds
Heated front screen energised for 2 seconds
Courtesy lights energised for 2 seconds
Dim dip relay energised for 2 seconds
Rear fog guard lamp energised for 2 seconds
Headlamp power wash energised for half a second
Front wiper energised for half a second
Rear wipe/wash energised for half a second
7. The MFU will then exit the diagnostic mode.

Does HRW always work with CC switch? as in not just the once when plugged in
Can you hear the relay click when you switch it every time?

Does the HRW switch work in another circuit?

If it works with different switch, and thats "works and heats the window" not just "light comes on" then wiring is OK

If it works constantly with a different switch, I would look at replacing it

If it only works once when plugged in suspect the connections

Things to concentrate on

Switch
Connections
Relay
MFU
SW

Cheers Elmer D.
If the switch is not working would the mfu test start?
Also what is SW?

Thanks.

Quick update on this one.

It turned out to be the switch. Took it apart, cleaned up the copper contacts put it back together again, and all is working again now.

is it the same on a disco 2 ?

dazand22 said:

is it the same on a disco 2 ?

Click to expand...

If u think to the MFU no ... D2 has a more complicated system named BCU