Brake Dashboard Warning Light

[gwiz22]

Under heavy braking, like approaching a roundabout, the dashboard warning light on my 1990 M100 comes on for a moment then turns off as soon as I release the brakes.
Any ideas on whether this is a problem or not?
Thanks in advance
Graham

[Fredjohn]

Check your brake fluid level. It's probably sloshing around under braking and operating the switch in the reservoir lid.

[HJ2]

[Rambo]

I agree with John and HJ too. Keep that brake fluid level topped up and the light will disappear.

And if your brake fluid is >2 years old change it and bleed the brakes. It is hygroscopic ie attracts water. DOT brake fluid is cheap so a relatively easy and cheap fix.

[HJ2]

Eeehrmmm…. Or you don’t top up the brake fluid. When the light comes on, you know it is time to change pads!
But then you need to drive it a LOT so the moment comes earlier then 2 years

[lotusflasherman]

Under heavy braking, like approaching a roundabout, the dashboard warning light on my 1990 M100 comes on for a moment then turns off as soon as I release the brakes.
Any ideas on whether this is a problem or not?
Thanks in advance
Graham

I suffered from that in one of my M100's for a long time. The fluid level sensor is a printed circuit board in the master cylinder fluid and that one was sensitive to fluid movement under heavy braking or cornering. Fluid WAS NOT LOW.
I then acquired a load of spare parts that included a used master cylinder and found the quick fix was to swap the pcb level sensor, which you can just manage to fiddle out the old, and the replacement in, without removing the master cylinder ... but it's tight.

I thought I reported it on here but it was many years ago...

[lotusflasherman]

Found it ... forum.lotuselancentral.com/viewtopic.php?f=41&t=25573&p=323601&hilit=fluid+level#p323601
as I said .. PCB became a vibration sensor not a fluid level sensor ..
also this ... https://youtu.be/GVJGlWSIZyo

[HJ2]

I had the same with the PCB on the HES. I hope it's not a trend!
So Gwiz... is the fluid low or not?

[dapinky]

Whilst all of the above are correct - one thing missing from all the posts is to check for fluid leaks!

Topping up a leaky system is not a great idea - and the fluid has to have gone somewhere......

...... hopefully it will be as Henk-Jan says, and the level has dropped due to pad wear moving the pistons out a bit - but worth checking for leaks before chucking a load in.

[lotusflasherman]

Whilst all of the above are correct - one thing missing from all the posts is to check for fluid leaks!

Topping up a leaky system is not a great idea - and the fluid has to have gone somewhere......

...... hopefully it will be as Henk-Jan says, and the level has dropped due to pad wear moving the pistons out a bit - but worth checking for leaks before chucking a load in.

Yes, I agree Dave but most people have the sense (I hope) to check the master cylinder fluid level when they get intermittent flashing of the warning light. If it's correct and it still continues to flash it is a failure of the printed circuit board fluid level sensor.
I posted a link to a video of my failed sensor in a preceeding post yesterday. What I didn't state explicity though, was that once it starts flashing due to vibration while under fluid it CANNOT BE TRUSTED TO INDICATE WHEN FLUID LEVEL FALLS. Evidence the video where it has no fluid so should energise the light but only does so when tapped.

[gwiz22]

Hi Chaps
Thanks you all for your helpful suggestions. I apologise for the late response. Shortly after posting the initial query I became poorly. Feeling more spritely now, I ventured into the garage, now oven, to check the fluid level. I couldn't quite make out the MAX mark. However the fluid was 12mm above the join of the two halves of the master cylinder, which looked fine to me. So, I guess I have the same problem detailed by lotusflasherman. I'm thinking of changing the master cylinder for the smaller bore Astra one so hopefully that will have a new sensor.

Thanks again to all.
Graham