Low Brake Fluid: Warning & What to Do

Hello,
I had the brake fluid changed at ATU.
As I was driving home and had to brake suddenly, the red warning light for the braking system briefly illuminated (it's the same light as for the parking brake), a warning sound went off, and the message "Stop: Brake Fluid" appeared on the information display.
The next day, I went back to ATU and complained about the issue. They then filled the brake fluid reservoir to the maximum level, but there was no change; the problem only occurred when braking heavily, before the ABS system started to engage.
After that, the system was completely bled again, but without success.
The technician removed the cap from the brake fluid reservoir and checked its mechanical function. He then inspected the front brake pads for wear, but everything was within acceptable limits.
After that, he told me about the stabilizer bar for distributing braking force between the front and rear axles.
He once had a similar case with a BMW where the linkage was broken.
He was somehow at a loss, so he admitted that he had reached the limits of his knowledge and sent me to a more experienced colleague.

So, I went to the friendly person with a good mood and told them the story.
There, you would press the yellow cap of the brake fluid reservoir, which incorporates the minimum level sensor (float switch).
It was replaced, but there's still no improvement.
During the test drive before changing the reservoir cap, I noticed that the warning message "Check brake fluid level" appeared even without touching the foot brake!
Unfortunately, it was the end of my shift, and I have to go back again next week.
Die Mechaniker wollen nächste Woche mal das Kabel das zu diesem Schwimmerschalter im Bremsbehälter-deckel führt überprüfen.Schwimmerschalter ist elekrisch und mech. I.O.

What do you think about that? Has anyone else experienced this problem before?
Unfortunately, the search didn't yield any useful results.

Okay, so I went back to ATU and wanted to find out who would be covering the costs.
The ATU manager told me to wait and see, and if it turns out the problem was caused by ATU, they will cover the costs. The VW master mechanic should contact ATU. The fact is, I've had this warning message ever since ATU changed my brake fluid!
And somehow, I think the ATU mechanic damaged the cable while removing the cover. Unfortunately, the fuse box for the auxiliary heater is located above the brake fluid reservoir, so it's a bit of a hassle to remove the cover, and that's where the cable might have been bent or stressed.

My vehicle is a Volkswagen Golf 4 manufactured in September 2001 with an ASZ engine.

Best regards, Jürgen.

Hello,

I would have sent the ATU "master" (idiot) to the moon with that sentence about the brake force regulator.
"Your Golf doesn't have this - Does the inspection report regularly say '8 spark plugs' because there are V8 gasoline engines?"

For me, it also sounds like a damaged cable, but several people have already checked that – or is that still being planned?

If the float switch is a normally open type, try bridging the connector and see if it works; if it triggers a warning, then it's likely a cable issue. If it's a normally closed type, leave it disconnected and see what happens.

What can we learn from this?
NEVER go to ATU unless it's -20 degrees outside and you're looking for a warm place.

Hello dieselmartin,
No, the VW mechanics haven't checked that cable yet.
"I haven't received any notifications about potential dangers when the plug is disconnected."
I can definitely look into that bridge thing.

What I've noticed is that the warning message only appears when I'm driving, i.e., when the wheels are turning.
While standing still, I can press the brake pedal as much as I want, but nothing happens.
I need to fiddle with the cable and see what happens.

Best regards, Jürgen.

Hello,
I just bypassed the connector, and immediately after starting the engine...
received a warning message.
It seems the problem is with the cable at the back.
Great ATU.
Changing the cable will definitely not be done in 10 minutes.
Does anyone know how long this usually takes, or what needs to be removed in order to reach the other end of the cable?
Hopefully, I won't have to remove the instrument cluster for this!

Best regards, Jürgen.

STOP!

The bridge system only works if the swimmer is a "opener." This is because with the bridge, you always have enough fluid inside, and any warning can then only come from the cable.

If he's a gatekeeper and closes the gate in the warning situation, then you've now created a situation where there is "always too little fluid" with that bridge.

I don't know whether it's a lock or an opener, so I can't tell you which of the two approaches you need to choose. I can only describe them to you.

Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

Okay, let's try without the bridge for now. Replacing the cable shouldn't be too difficult and should go quickly. If something is broken, it's likely where someone has been working on it. So, it could be directly on the cover.

I still think you need the bridge. If it's a cable break, it's less likely that there would be a short circuit between both cables. It's more probable that there's a break in one of the cables. If there's a break and the lamp is lit, then the circuit is normally closed. But if it's not an open circuit and the cable only makes contact when the lamp lights up, then the float must be broken again... Although sometimes, the improbable happens.

Herr Antje wrote:

So, in this case, let's try without the bridge. Changing the cable shouldn't be too difficult and will go quickly. If something was broken, it would likely be where something was worked on. So, it could only be directly on the cover.

I think he's concerned because the damage might not have been self-inflicted, and the problem may persist even if the switch is bypassed, in order to achieve the most reliable repair. It seems like he believes that a simple cable clamp won't be sufficient. However, I also can't imagine that the cable has another detachable connector somewhere, and disconnecting the entire wiring harness for something like that would be something I'd avoid.
I'm also suspecting it might be related to the cable connection in the engine compartment, as things are very tight there for me. Besides that, ATU can also handle all sorts of things, and you won't be able to figure it out on your own.

If he's really sure it's a broken cable, it probably needs to be "repaired" or "fixed." Anything else (as far as I know) would be a huge amount of work. I don't think they'll do it any differently or with higher quality at the dealership. Unless they're using Wago connectors, it won't be noticeable and it will still hold up.

I would immediately go to a friendly mechanic and have them do the work themselves, as ATU has to pay for it. They should then carry out the inspections.

My experiences with ATU weren't the best either...

Hello,
I have just simulated the water level sensor in the lid.
Brake fluid level max (float at the top) = no flow.
Brake fluid level at minimum (float at the bottom) = Pass.
I'm curious to see what they find when they do their morning check!
Okay, I have the wiring diagram available. It's included in Etzold's repair guide.
Something isn't working when I try to attach an image.

Best regards, Jürgen.

Herr Antje wrote:

So, in this case, let's try it without the bridge.

That's exactly what we should try now.

Herr Antje wrote:

I still think you need the bridge. If it's a cable break, it's less likely that there will be a short circuit between both cables. It's more likely that there will be a break in one of the cables. If there is a break and the lamp lights up, then the circuit is normally closed. But if it's not an open circuit and the cable only makes contact when the lamp lights up, then the float must also be broken... Sometimes, however, the improbable happens...

You don't need the bridge. What I considered unlikely turns out not to be so unlikely. If it's a cable issue, you would have a short circuit (both cables are in contact). Otherwise, one of the cables wouldn't be grounded by the other cable, but rather by the car body (I don't know the wiring diagram).

It's possible that the fluid level isn't horizontal due to strong braking (due to inertia), and it continues to drop because of air in the system. In that case, the reading would be accurate. Bleeding the brakes a second time might not help; sometimes, you need to activate the ABS with a diagnostic tool to properly remove the air.

Hallo H. Antje,
I can send you the wiring diagram by email.

You mean the level drops so significantly that the reading would be accurate.
I don't believe that because, after my complaint, the ATU employee filled the fluid reservoir completely full, and there was no improvement.

Best regards, Jürgen.

Hello w123diesel,
"Thank you, I don't need the wiring diagram; in this case, it will be handled by the dealer anyway. I wanted to offer an additional possibility that could cause this phenomenon. That's why I mentioned the sensor, cable, or fluid."

The fluid level is probably not the issue, as I heard that you could empty the container from maximum to below minimum with just one pedal stroke (which is quite a lot). I once had an air bubble in the ABS hydraulic unit, so it's certainly possible.

Full to the brim?

aaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhhhhhhhhhhh

What kind of...

That's also why the MAX marking is there.

dieselmartin wrote:

Edge full? aaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhhhhhhhhhhh What kind of... That's also why the MAX marking is there.

ATU hold...

Perhaps I missed something: Is there an error log? Warnings caused by fluid movement during braking can be ruled out unless the level is actually below the minimum. Maybe the people at ATU messed with the fluid so much that the connector also got soaked. Does the yellow cap show any signs of damage?

Hello,
There is no error entry.
The lid, including the float switch and connector socket (a complete unit), has already been replaced with a new part, but there is still no improvement.

Jürgen.