Brake Low Pressure Warning Light Coming On

Question: Dear All. My SSI (SRX15236) has a similar problem. The left Low pressure warning light is standing on. After having changed the master cylinder (it was leaking) and after numerous bleeding (there was always air comuing..) my engineer and myself noticed that there was a small leak of braking fluid on the hydraulic pump corresponding to the burning warning light. The leakage is just underneath the circlip. We have changed the 2 outer o rings. the leakage was smaller but still present. The pump works and there is enough pressure to brake, but the low pressure light is still on. I believe that there might be a problem with the pump itself (maybe with the non return valve). My idea is to order (@flying spares) a reconditioned brake pump barrel & the outer O rings (and a removing tool, obviously). As there is air in the circuit, I think that the problem should not be in the accumulators.

Answer: If the brake pressure warning light is coming on then 
the MOST likely unit to be at fault will be the brake accumulator sphere (especially if the car has been standing for a long period of time) - RH2390SXR or UE37237SXR but please be aware that:
1. You need to ensure that the brake pressure switches are working correctly (UD18723SXR)
2. That a fault in the accumulator valve body can cause the low pressure light to come on. You have to remove the valve body in order to replace the sphere so we recommend strongly that you either replace or overhaul (seal kit is RH2435) the valve body (UE37583SXR or UE35843SXR) at the same time as replacing the sphere.
3. If a brake pump (UE40534HBSXR) fails or a push rod (UE36794P)snaps then this will also bring on the low pressure warning light

Question: Thank you for the reply. I will try to swap the pumps (do I have to swap the pumps or is it enough to swap the pipes?). Yes the car has been standing unused for some time (6/7 months), but, at that time, the low pressure problem was already present. Is it possible that the nitrogen contained in the spheres "lasts" so long (i.e. after more than one year there is still air coming out)? Although the warning light is on, by braking you do not realize that there is "less" pressure than before. I could change the pump first and then, if the problem is still existing, I could change the sphere. In that case a reconditioned sphere would arrive already "filled" with nitrogen?

While I was bleeding the car for the first time I noticed very "dirty" brake fluid (less than 1/4 pint) and I suspect that this could be the evidence of a past use of the wrong brake fluid. The car has been checked and there are no other leakages than the one mentioned above.

I am glad to have discovered a part supplier which provides such an helpful service! (Pitty that my car is too far to be serviced by you...)

Answer: We agree that the brake pump needs replacing because it is leaking but we are still concerned that you have a problem with the accumulator sphere. The two brake pumps are identical so if you swapped them over and the right hand warning light was then staying on you would be able to confirm that the brake pump is the sole cause of the low pressure. But because you have a lot of air in the system we are concerned that the rubber diaphragm inside the sphere has persihed and is allowing nitrogen to pass into the fluid. Has the car been standing unused for long periods of time ?

You will need to swap the pumps I am afraid so the first thing you will need is the tool RH8428P. If the nitrogen has passed through the sphere diaphragm into the fluid then it will stay in the system until it is released when bleeding. The reconditioned spheres do contain nitrogen so all you have to do is fit them and bleed the system. The dirty fluid is a worry - I would recommend removing the lid of the brake fluid reservoir and having a look inside - if the car has been contaminated with the wrong fluid (usually LHM) then a sludge will usually have formed in the bottom of the reservoir. If the car has been contaminated then the incorrect fluid will probably have caused all the rubber in the hydraulic system that it has come in contact with to swell and break up leading to the formation of the sludge. Unfortunately you will then need to replace every rubber hose and seal in the system in order to fully decontaminate the car. If the car appears to be braking efficiently then your problem may lie in the accumulator pressure switch (again this can be checked by swapping the two switches) or in the valve body. Good Luck.