RangeRovers.net Forum banner

1 - 4 of 4 Posts

·
Registered
Joined
·
29 Posts
Discussion Starter #1
Chaps,

The heated rear screen on my 2006 Sport S/c is permanently on. This is whether the switch is on or off (lit or not) or the engine is running or not, even when it is locked on the driveway!

There is a current drain of 5amps all the time until I remove the rear screen fuse, which drops the current drain to 0.004amps.

A bit of research on the net (dangerous I know !!) would indicate that on other older vehicles (Defender, P38, etc) that a voltage sensitive switch prc4427 might be to blame. However I'm not sure the Sport has this part number (or where it is located) or indeed if this is the problem.

Any help gratefully received before I head (gulp) to the main dealer.
 

·
Premium Member
2006-2009 Range Rover Sport
Joined
·
5,175 Posts
I don't have a wiring diagram for this (but I'm sure "someone" here does :D ), so I'm gonna assume the RRS is like other cars (sometimes a bad assumption) but there should be a timed relay for the rear defrost--maybe owners manual shows location, idk.

Check it first. Pull the relay, check it for burning smell, if there's no smell check/clean the contacts, put it back and see if problem goes away. But, before ripping apart the dash to check the switch, it may be worth it to replace the relay anyway to see if that fixes your problem.

If relay proves OK the switch should be checked next.

But there's always the chance with the RRS that all this goes through a $2000 control module :doh:
 

·
LIFETIME CONTRIBUTOR
2006-2009 Range Rover Sport
Joined
·
11,013 Posts
Here is what I put together: Description of rear window heater operation, picture of CJB (fuse box behind passenger compartment glove box) and pdf of wiring diagram for the rear window heater. Suspect stuck relay switch R138 on CJB, per enclosed electrical diagram. The ATC module is probably $2000 like goosey said, so let's hope not... Good luck!

Rear Window Heater
The ATC (automatic temperature control) module controls operation of the rear window heater using medium speed CAN (controller area network) messages to operate the rear window heater relay in the CJB (central junction box) . The control module in the CJB (central junction box) interprets the CAN (controller area network) messages and switches the ground connection of the relay coil to operate the rear window heater. While the rear window heater relay is energized, a battery power feed is connected to the rear window heater elements. Rear window heater operation is only enabled when the engine is running.

The ATC (automatic temperature control) module operates the rear window heater in heating cycles of varying power and time. The heating cycle used depends on the ambient air temperature and whether it is the initial or subsequent operation during the current ignition cycle.

When the rear window heater switch is pressed, the ATC (automatic temperature control) module illuminates an LED (light emitting diode) in the switch and initiates the appropriate heating cycle. The LED (light emitting diode) remains illuminated until the rear window heater is selected off, the heating cycle is completed or the engine stops. If the engine stalls or the ignition is turned off, rear window heating resumes if the engine is re-started within 20 seconds.

On the initial selection of rear window heating, the ATC (automatic temperature control) module uses a short or long defrost phase at full power, followed by a low power phase. The defrost phase used depends on the ambient temperature. During the low power phase, the rear window heater relay is cycled off for 80 seconds and on for 40 seconds.

On subsequent operations, during the same ignition cycle, the ATC (automatic temperature control) module operates the rear window heater at full power for a fixed time period.

Rear Window Heating Phases
Phase Time, minutes
Short defrost (-5°C (23°F) and above), 10
Long defrost (less than -5°C (23°F)), 15
Low power, 20
Subsequent operation, 10
[attachment=0:wb90noe3]CJBpic.jpg[/attachment:wb90noe3]
 

Attachments

·
Registered
Joined
·
29 Posts
Discussion Starter #4
Gents, thanks for your help. This really is a fantastic resource full of knowledge!

Umbertob, I think you are probably on the money with the R138 relay. Is it marked R138 and am I right that it is on the fuseboard behind the glovebox?

Next daft question, is it LR specific or widely available (runs off to search Google and Ebay)?

P.S. Your Sport is lovely, they look fantastic in white.
 
1 - 4 of 4 Posts
Top