So as I went out to start my truck for its warm up this morning it was covered in the first frost of the year. I went to push the button for the rear window defrost and the light on the button did not come on, and the button would not stay engaged, and the defrost didn't come on.

Im thinking its either a bad button, fuse, or short somewhere. Anyone have any ideas?

 

How long have you had your truck?
Did it work last year?

 

See attached from RAVE circuit diagram. Could be fuse or relay (if lucky) or MFU (if not so lucky). MFU controls all sorts of things that need timimg, like dome light dimming, etc. It is on the back side of the fuse holder on driver's side. PITA to get at and replace, you want battery disconnected when doing that.

 

Only had it since march and this was the first time trying it. And ill be checking out all the fuses etc after school tomorrow. Is there anyway to diagnosis the MFU?

 

Here is how to test:

Land Rover Discovery Multi-Function Unit Diagnostic Check
Posted by okdiscoguy in LR Enthusiast Forum (8-24-2007)

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 operated.
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.

 

Are you pressing the top button on the left side of the instrument cowl?

 

Holy crap Spike, that's what those are for? I've never used them as they've never worked since I've had mine. Then again the entire instrument cowel is missing the two lower screws that hold it in place. Then again in AZ it's really never too necessary for the DF but, maybe I'll check a few fuses this weekend.

 

I checked fuses and they are all good. Could not get MFU in diagnostic mode. The dome lights and all other dash buttons work as they should. So im not assuming its the button.

 

I'll be doing the same diag tomorrow BRad, I'll let you know if I find anything interesting or useful.

 

Thanks. And I Meant im assuming it is the button. I might try switching the rear fog light button for the defrost just to see if I can