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| blackwolf Member Since: 03 Nov 2009 Location: South West England Posts: 17382   
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If the switch seems to work ok (ie the light comes on) I would be more inclined to suspect the main relay or the timer relay under the offside seat.
If you have a wiring diagram (available vis this forum) and a multimeter (not available via this forum!) it should be reasonably easy to troubleshoot. |
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26th Feb 2013 4:36pm |
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| Defpuma Member Since: 10 Feb 2013 Location: Kent Posts: 84 
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Thanks for that Blackwolf.
If the switch light doesn't come on each time would that lead you to think that there was a fault with the switch or loose connection at the back of the switch somewhere? Apologies but not too hot on electrics!! |
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27th Feb 2013 12:44pm |
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| blackwolf Member Since: 03 Nov 2009 Location: South West England Posts: 17382
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Let me have a look at the wiring diagram and get back to you on that.
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27th Feb 2013 4:12pm |
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| Mattyboy Member Since: 05 Dec 2012 Location: Sudbury Posts: 58 
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I too would be interested to know, my switch doesn't light up and the screen doesn't clear 07 Defender 90 TDCI
98 Defender 90 300 Tdi Land Rover Freelander MG B GT CBR 600 AEC Matador but no washing machine |
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1st Mar 2013 3:04pm |
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| blackwolf Member Since: 03 Nov 2009 Location: South West England Posts: 17382
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My apologies for not posting back sooner on this!
There are (unfortunately) several components which could fail in the HFS circuit and any one of them will produce much the same symptoms, ie no light on the switch and no heat from the screen. The first and easiest thing to do is to check fuses 15 and 36 in the Central Junction Box (the CJB is the fuse panel under the dash, not the one in the seat locker which is the Battery junction Box or BJB). Fuse 15 is an ignition-controlled 5A fuse which powers the HFS main relay via the timer relay. If this has failed the main relay will not energise. Fuse 36 is a permanently-live 30A fuse which powers the screen via the main relay. If both fuses are OK, probably the simplest next step in troubleshooting would be to replace the main relay and timer relay in turn with new or known good units (KGU). The main relay is fairly cheap, the timer relay is quite expensive. Since the timer relay is more complex, it is unfortunately more likely to fail than the main relay. If you are technically savvy you can test the main relay as follows, but you do this at your own risk. Remove the timer relay from its socket (connector C1624) and connect a 5A fused live to pin 8 in the socket. If the screen heats up (the ignition doesn't need to be on), then both the main relay and screen itself are OK. If not, replace the main relay with a KGU and try again. Note that the tell-tale in the switch won't light up during this test. It is virtually impossible to test the timer relay except by substitution. You can however put a voltmeter between pin 5 in the timer relay socket (C1624) and earth to test the "Eng Run" signal from the instrument pack. You should see 0V with the engine stopped and +12V on "Eng Run" when running. In C1624 there should be an ignition controlled +12V supply on pin 4 (from Fuse 15), and a permanent earth on pin 2. The switch itself is difficult to test (since it is a momentary contact type) but with the swtich removed from the car, connecting +12V to pin 5 on the switch and ground to pin 1 should illuminate the tell-tale. Move the ground to pin 4 and the tell-tale may illuminate momentarily as the switch is pressed. Aside from these tests, really the quickest and easiest way to diagnose HFS faults is by substitution of the timer reley, main realy, and switch in that order with known good units. It is ideal if you know someone with a working one who will let you swap parts to test. Hope this helps a little. |
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11th Mar 2013 10:23am |
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