S1: Hydraulic Warning Light (!)

[Michael P]

This is a cross post in the Hydraulic/Electrical section


I don't know if this seems to be a common problem but I have this light coming on and it stays on for a while after I start the car and get going. Then it extinguishes. It occasionally comes up for a few seconds while driving.
I don't think there are any hydraulic pressure problems to warrant the light coming on.
Judging by the poor circuits that I have, the wiring in the instrument cluster should never allow this light to come on on its own WITHOUT the stop light. The rare expeption may be when the oil pressure switch warning light bulb has died. In my case the STOP light does NOT come on. All bulbs are in working order. Has anybody perhaps got a reasonable explanation or better circuits?


Thanks


Michael

[noz]

Hi Michael,

You've really got two issues there in one explanation.
1. Light takes a while to go out when starting in the morning
2. Hydraulic pressure light on without the stop light

We'll deal with 1. in the hydraulic section and 2. in the electrical section.

Here goes:
I'm not aware that the S1's were fitted with the anti-sink feature. This means that overnight the fluid lost from the leaks finds its way back to the reservoir. When the car starts in the morning the 'lost' fluid needs to be replaced just to get the car back to where it left off the night before. It takes a finite amount of time for the pump to transfer the required fluid from the reservoir in to the hydraulic system. This is the delay you see in the light going off. This delay is made much longer the lower the static pressure there is in your spheres to begin with. With low sphere pressure, much more fluid has to be pumped into the system to achieve the pressure at which the bodyshell starts to lift off the bumpstops. The more fluid it requires the longer it takes to pump it up. This time can be reduced if you increase the rpm (and hence pumping rate) at start up by revving the engine (not so good for a cold engine). The problem does not have to be all of your spheres. However, the more 'flat' spheres you have the worse the problem gets, its proportional.

As for the light coming on whilst your driving, did you notice, is it related to turning corners? If so it could be one of two things:

a)The fluid level in the reservoir is slightly too low. As you go around a corner the fluid is forced to one side and the level probe thinks the tank is empty. The light on the dash comes on momentarily until the corner has passed and the fluid level returns to the flat position which is just OK.

b)The other potential problem is a flat accumulator sphere. The power steering is very greedy when it comes to the use of hydraulic fluid. If you turn the steering the system sees a momentary increase in consumption. It is too fast for the pump to make up on its own so its helped by the stored pressure in the accumulator sphere. The steering only consumes the fluid when it is actually moving. Once the wheel is turned into the corner and the car is on its way around the bend the fluid consumption stops. During this time the pump has a chance to catch up. Once the bend in the road comes to an end then the steering wheel is turned back to the straight ahead position. In doing so it momentarily increases its consumption again. Once on the straight the consumption reduces back to the background level again. A 'flat' accumulator sphere will not be able to provide stored pressure to the system in instances of high demand so you get a momentary drop in pressure with the light coming on on the dash. As soon as the pressure recovers the light extinguishes again.

When the engine has started and the car has reached its normal ride height, what is the time interval between clicks from the pump/regulator? Anything from 30 secs to 1 min is OK to good. Anything from 2-15 seconds is bad and indicates a 'flat' accumulator sphere (or a big leak somewhere).

Can we have a few more symptoms or a more detailed description to narrow down the possibilities?

Cheers

noz

[Michael P]

Thanks Noz for your detailed reply. Yes, my accumulator sphere is not the latest, I am aware of that and I have again air in the rear brakes.
No, AFAIK I don't have an anti sink feature. The light comes on usually in the morning from starting. The car rises fairly swiftly though (I had others that took ages on even new spheres) and once it is up the light stays lit. I start to drive and it is still on.
The light may then extinguish after about 3 minutes of driving.

The liquid level is OK. I am aware that it can flash once you go through corners and the level is low. But on my BX the stop light came up as well if I recall correctly.
I know the PS is heavy on pressure consumption but although my accu and pump needs replacing (I have one ready) it does NOT come on. In fact it never comes on even when turning for parking when the steering occasionally gets heavy. I cannot make this light go on at will.

Once the light is off it very infrequently seems to light up for short intervals, maybe 10s max. Again WITHOUT the stop light coming on. Normally when driving straight ahead. I do not recall it coming on during any evident maneuvers.

I am about to install a new pump, new fluid and accu.

Regards


Michael