Help figuring out cause for a BRAKE warning light - LotusTalk - The Lotus Cars Community
 
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post #1 of 7 (permalink) Old 02-15-2010, 05:13 PM Thread Starter
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Help figuring out cause for a BRAKE warning light

When I purchased my 1986 Turbo Esprit HCi the BRAKE warning light on the dash was constantly on. I have been trying to figure out why. I assume it is warning me that the brake fluid is low. I made sure that the fluid reservoir is full of brake fluid. Next I tested the cap on top of the reservoir with the two connected wires to make sure the low fluid switch was working...it is. Just for good measure I replaced the cap to be sure the switch was ok. The BRAKE warning light is still on. Tonight while looking around for other possible problems I noted what I show it the two pictures attached. In the first picture Attached Image there is some sort of off-white plastic device that connects the bottom of the servo-brake booster. I noticed that the device has a nipple for a hose connection but there is no hose connected to to it (see arrow). Anyone know what the off-white plastic device is? Should the open nipple be connected to something? My next questions are about the second picture Attached Image...coming off the servo-brake booster is a black hose, I assume a vacuum hose, with an in-line tee connector. The smaller hose coming off the tee is capped and nothing is connected to it. It is possible that the nipple without anything connected to it and hose coming off the tee without anything connected to is might be related? My final question...any ideas on what I might check that would cause the BRAKE warning light to remain on? The brakes on the car seem to work just fine. HELP!
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post #2 of 7 (permalink) Old 02-15-2010, 06:25 PM
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Not sure on that year but it might be the emergency (parking) brake is on or the switch is not adjusted correctly. Make sure the parking brake is ALL the way down. If it is all the way down pull one of the wires off the switch and see if that kills the light.
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post #3 of 7 (permalink) Old 02-16-2010, 07:41 AM
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I haven't worked on brakes for a very long time but the way things USED to work: The switch detects a pressure difference between front and rear brake systems - if the pressure is the same in both system the actuator doesn't move, if the pressure is lost in either system the actuator moves one way or the other. Even if you fix a leaky brake you need to send the actuator back to the neutral position. Open either front caliper bleed screw just a wee bit then step of the brake w/ increasing pressure. You should see the light blink off. If not open a rear bleed screw instead and step on the brakes until the actuator is centered. Someone before you may have bled the brakes w/o resetting
the switch. You should see a wire or two coming out of the master cylinder if this is the case, not just wires to the cylinder cap.
Looking at the white plastic thingy- unplug it and see if that helps. If not unplug it then short out the two wires and see if that helps. From the photo if appears to be a brake vacuum failure switch.

Last edited by billt; 02-16-2010 at 07:58 AM.
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post #4 of 7 (permalink) Old 02-16-2010, 09:53 AM Thread Starter
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Thanks for the tips guys. The parking brake has a separate warning light so I know the BRAKE warning light is not caused by the parking brake. I'll try the other tests that were mentioned. Many thanks again.
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post #5 of 7 (permalink) Old 02-20-2010, 07:45 AM
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I'd say your hunch about the missing hose might be on target. The white object may be a vacuum switch, and the light could be an indication that vacuum to the booster is low.
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post #6 of 7 (permalink) Old 02-21-2010, 10:05 AM Thread Starter
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I'd say your hunch about the missing hose might be on target. The white object may be a vacuum switch, and the light could be an indication that vacuum to the booster is low.
That's my guess Sanji. I have hooked it up so we will see. Unfortunately I am in the midst of replacing my clutch master so I can't yet start it up to see if that fixed the problem. I'll let folks know what happens.
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post #7 of 7 (permalink) Old 02-22-2010, 05:35 AM
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You should be able to unplug all switches involved w/ braking - the vacuum switch and any connections you see at master cylinder. This should make the light go out even w/o starting the car. Then plug them back in one at a time to find the culprit. I imagine the rubber diaphram in the vacuum switch is rotted out and you'll need to replace the switch or leave it unplugged.
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