Had an issue with my heated front screen for a year now. Dealer wants 850 to correct this but won't tell me the issue. My guess is they don't know and want to change everything. Basically it won't work. Fuses are ok but the switch won't light up. Have changed switch still the same. Any clues please

 

see attached - prime suspect would be the MFU, a multifunction timer on the back of the fuse panel. Shop manual has a test procedure for the module.

 

Sorry - here's the test procedure you can do at home for the MFU.

Pix of internal as well. It is a small box on the back of the fuse panel, times lots of things in the truck, and is not really something to tinker with unless you like component level printed circuit board repair. Not a well designed unit, I replaced one because it had melted a hole in the case by overheating. Change out interior dome lights and cargo light bulbs to LED to improve life of the MFU (reduces power that must be "dimmed").

 

Are you getting power to the switch? If not, start working your way back with a test light or multimeter.

 

If it was the MFU, wouldn't there be issues with other things along with the heated windscreen?

I am having the same problem as the OP (heated windscreen not working).

My switch light comes on, all fuses are ok but no juice at the connectors in the cowl.

I ordered a relay, hopefully that will do it. I will post up after I put it in.

 

Did you not test your relay before ordering a new one?

 

No, didnt know how to test a relay so I got a known good used one for $4 shipped to my door.

How do you test a relay for future reference?

Thanks!

 

The MFU can die on just a single function, or more than one. The file I attached is the RAVE method of starting a demo test cycle that runs thru them all, so you can verify the module is operating things. No hand tools required, just hands.

Pressing the switch requests the MFU to engage the relay, which powers up the front screen elements and lights the button. So if pushing button does not make a click, it would be relay or MAF. And without turning yourself into a pretzel the above posted test diagnostic will test the MFU. When you have to replace it, you will find the reason it is called the MF U. Suggest you disconnect battery when trying to move the fuse block around....

 

Thanks S.B.

So it's either the relay or MFU I guess. I will check the MFU per the RAVE and plug in my new relay. Here's hoping its the relay!

 

I replaced my MFU chasing the dome lights, and the rear wiper started working (it was way down the list). It is replaced in the D2 with the more complex BCU.