FLICKERING BRAKE PAD WARNING LIGHT WHEN HANDBRAKE APPLIED??

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lrjohn

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The brake pad wear warning light on my Discovery 1 flickers when the handbrake is applied, ignition on, never goes to a solid light. This is the only time the brake pad warning light comes on, all of the brake pads are fine.

Someone suggested it might be a bad earth, or possibly a partial sorting out of the wiring ribbon on the back of the instruments.

Anybody had the same problem and found the cause? The MOT is coming up for this vehicle and am wondering if this would be a reason for failure?

As usual, any comments will be much appreciated!
 
tilly2 said:
If you look in the handbook, Im sure thats the "parking brake applied" warning light
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I was a bit stumped and made some research, seems that the OP was misled exactly by the owner's manual which is wrong and in contradiction with the reality as there are no sensors for brake pad wear like on more modern modells cos in reality this warning can be triggered only by the handbrake switch or brake fluid level sensor but as it flickers only on handbrake it's most probably that switch or it's wiring to earth

... or LR made the fluid level switch so sensitive to trigger the warning for a few mm fluid level drop which can be caused by pad's wear :rolleyes:


o_O Owner's manual:

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sierrafery said:
o_O I didnt know that the D1 has such thing... didn't you mistype the modell by any chance?...if it's about a D1 which particular warning light is it?
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Thanks for your response, very definitely a early D1 V8 registered 1990, Jay as they are sometimes called - I was surprised to find brake pad wear connections when I started stripping down the front brakes but it definitely has them.
Photo below shows the lights, parking brake on to the left of the the seat belt light, brake fluid low warning light on the opposite side of that and centre bottom row is the light I am referring to which flickers. This should go out when the engine is turned on sometimes doesn't – so the only thing I'm now thinking is possibly a faulty sensor?


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lrjohn said:
Thanks for your response, very definitely a early D1 V8 registered 1990, Jay as they are sometimes called - I was surprised to find brake pad wear connections when I started stripping down the front brakes but it definitely has them.
Photo below shows the lights, parking brake on to the left of the the seat belt light, brake fluid low warning light on the opposite side of that and centre bottom row is the light I am referring to which flickers. This should go out when the engine is turned on sometimes doesn't – so the only thing I'm now thinking is possibly a faulty sensor?


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o_O Very interesting, LR can always surprise me... unfortunately i can't find anything about that warning in the official documents i have nor in the diagrams but if it flickers only when the handbrake is applied those sensors might share the earth with the handbrake switch or something...if it was a "wear sensor" it should trigger the light regardless of the handbrake's action IMO

what if you unplug all those sensors? IMO that warning should rest then
 
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usually the brake pad sensors just earth a wire to illuminate the lamp, most likely the power is supplied from the hand brake warning circuit so pad warning only comes on when parked. Probable cause of problem is the sensor wires have rubbed through the insulation and are touching the body somewhere. I had similar prob on RR classic years ago
 
PaulJM said:
most likely the power is supplied from the hand brake warning circuit so pad warning only comes on when parked.
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All the warning circuits are getting ignition power supply through the instrument pack's pcb they are not interdepandant, once the ignition is on they all have power. On later D1's which dont have brake pad sensors the handbrake warning has the same ignition supply with all the other warnings and they come on once earth is switched on each lamp's earth path by the corresponding switch or ECU when it's involved ... the handbrake/low brake fluid/(in this case the pad wear) warnings should come on while driving too if that's the case not just when the vehicle is parked hence my pressupositon
 
lrjohn said:
The brake pad wear warning light on my Discovery 1 flickers when the handbrake is applied, ignition on, never goes to a solid light. This is the only time the brake pad warning light comes on, all of the brake pads are fine.

Someone suggested it might be a bad earth, or possibly a partial sorting out of the wiring ribbon on the back of the instruments.

Anybody had the same problem and found the cause? The MOT is coming up for this vehicle and am wondering if this would be a reason for failure?

As usual, any comments will be much appreciated!
Click to expand...
The brake pad wear lamp should never be on when the handbrake was applied.
It only happened a couple times in the 100,000 miles I did In my 1987 RR, as it should, indicating a brake pad was worn somewhere when the brakes are applied.

Early disco had the same electrical system as the early RR so if your after a electrical wiring diagram you’re find it in the early RR workshop manual.
Which u may be able to download now or not.

There’s definitely no ECU involved, maybe you don't have a fluid level sensor fitted like my RR. But If so it’s fitted as part of the fluid filling cap.
 
I was intrigued by this fault cos it's very strange and i made some research... i presumed that the early D1's system is similar with the RRC based on PaulJm's reply but now it's almost certain confirmed by discool so i'll reveal my findings based on RRC '89 diagram and description(relevant parts attached).

there should not be any relation at all between the handbrake and the brake wear warning so if the lamp comes on then not going out/flickering after the ignition means there is a problem with the sensors or that particular circuit cos the brake wear warning's self test is managed by the same relay like the brake faiure warning(right side of seatbelt in the dash pic). I can't imagine how this system is in reality cos there are only two "sensors" which are managing this light named "right front and right rear inboard brake pad" in the WSM description.

in a nutshell, if the problem is with one of those sensors unplugging them should keep the light out as there is nothing to complete the earth path but if this doesnt help it can be complicated

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sierrafery said:
I was intrigued by this fault cos it's very strange and i made some research... i presumed that the early D1's system is similar with the RRC based on PaulJm's reply but now it's almost certain confirmed by discool so i'll reveal my findings based on RRC '89 diagram and description(relevant parts attached).

there should not be any relation at all between the handbrake and the brake wear warning so if the lamp comes on then not going out/flickering after the ignition means there is a problem with the sensors or that particular circuit cos the brake wear warning's self test is managed by the same relay like the brake faiure warning(right side of seatbelt in the dash pic). I can't imagine how this system is in reality cos there are only two "sensors" which are managing this light named "right front and right rear inboard brake pad" in the WSM description.

in a nutshell, if the problem is with one of those sensors unplugging them should keep the light out as there is nothing to complete the earth path but if this doesnt help it can be complicated

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Excellent! Thank you so much for that investigative work – I shall look further on the vehicle!
 
lrjohn said:
Excellent! Thank you so much for that investigative work – I shall look further on the vehicle!
lrjohn said:
Excellent! Thank you so much for that investigative work – I shall look further on the vehicle!
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Thought you might like to know what happened with this. I have been right through the braking system, change the fluid, serviced the callipers and on the rear replaced the brake pads. Rear driver's side has a pad with the wear sensor, I replaced this and problem went away! However, the pad I replaced was were nowhere near worn to the point where I would have said it would it would have brought the brake warning light on but some how it must have have been the cause as the problem is fixed
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