P38 Heated rear Window

Which window?

Disco 2 automatically gives you rear window heating when the defrost setting for the front is for the front is selected. The rear heater selector switch warning light is however illuminated.

I'd expect the front screen heater to behave similarly if you have the heated front screen option.

Did you have on?

Heated rear window. Prog was off. Prog switches on front and rear screens but always illuminates the orange display lights. In this case the window de-frosted but there was no light showing. I have considerable whine from the alternator leading me to believe it is on all the time. Could it be a faulty relay?

David

Start her up and measure the voltage across the terminals on the HRW element.

The Mundaneo switches front and rear screen heaters on automatically with temperature. The telltale lights show that they are on, however. I can't remember if the RR did the same, but I know it had the quickest screen defrost ever - about 10 seconds from iced over to clear and ready to go. Brilliant.

could be the becm

11.97 with engine started. Switching on and off makes no difference. 10.45 with ignition key removed. There is no apparent battery drain so it must go off with the interior lights etc.

David

I have had intermittent clicking from this unit recently but it has stopped - for now.

David

What should the voltage be Dave? There is 10-12V there all the time. The HRW will not 'switch off' other than by removing the fuse.

If there are volts across the element the diagnosis that it's not switching off is probably correct. Stuck relay, knackered solid state switch or BECM throwing a tizzy fit and keeping it on. Are there any audible clicking noises when you operate the HRW switch? With ignition on but engine not running 'cause of the noise.

The HRW switch will not operate without the engine started so I can't tell if it's clicking. I doubt it is because although the switch light works normally, the voltage is still there across the element even when it's off. I thought it might reset after removal of the fuse. I notice two relays in the under-bonnet fuse box - but both these are for the heated front screen. Do you know where the dodgy culprit is that controls the HRW? There was some clicking from under the seat a while back - sounded like a relay. Hopefully not the BECM??

Thanks David

Definately seems to be stuck on. Need to find the relay and trace the wiring checking voltages etc. Is the relay stuck on because it is being told to be on or have the contacts just stuck together?

Not on a P38, and only vaguely on a DII where I think it's in the inner workings of the auxillary fusebox in the passenger compartment.

Wouldn't have thought so for the relay, it still could be faulty but you need to find the relay first and see what that is doing.

I don't know if you have the circuit .... but it's in the e-mail anyway.

Many thanks. I'll do some detective work...

David