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brake warning light keeps coming on on the A4, checked manual and it says may be low on fluid, checked and i cant even see where the fluid is so assuming this is the cause. Hoping there isnt a leak too!!
So can I just get any old DOT4 from halfords/local garage, or will it have to be the really expensive audi approved stuff?
It'll have to match what's already in there. DOT4 and DOT5.1 can be mixed; DOT5 is 'different' and doesn't play well with others.
DOT 4 is a standard, so in theory, anything rated DOT 4 will be to spec.
Sometimes it is impossible to see the fluid clearly because it is fairly clear, and the reservoir dirty.
I would say any dot 4 as it should all meet the standards. The full answer is they may not be all the same but they will all meet the standard. Some will be really expensive and high performance but you won't notice any difference.
But if your fluid is going down then you have a leak. It doesnt just disappear.
Someone may come along and warn you that Audi say only use their stuff, in which case it's your choice but priority should be on getting some in there and then getting it checked for a leak. It sounds like you may have already sucked some air in the system anyway so they will probably need a bleeding anyway.
is it the low pad light?
I work in the clutch team for a large global automotive OEM - the brake and clutch fluid is the same and shares the same reservoir. I know for a fact that different brake fluid manufacturers dot4 can have different results on rig tests. mainly noise issues.
I would suggest nothing bad will happen if you put in decent clean branded DOT4, but to be absolutely 100% sure you will not introduce a potential noise issue later on in the vehicles' life, use the OE stuff from the dealer.
But if your fluid is going down then you have a leak. It doesnt just disappear.
well, yes and no. the audi almost certainly uses a concentric slave cylinder made by FTE, or Luk, and every time you actuate the clutch a very small amount of brake fluid is wiped onto the guide tube. Is it very small though. acceptable loss is something like (according to the suppliers) is in the order of parts of a ml in 10s of thousands of applications.
Check your brake light switch, the switch under the pedal. This is a common fault on VW and Audi cars. See if the brake lights go on when you press on the pedal, if not it could be the switch is gone. On my car the switch cost about £7
interesting Rusty Mac, i just chnagd one of the brake lights... any connection?