Low Brake Fluid signal and Brake signal on the dash board on Pontiac Montana 2003

Wow. I'm pretty sure something got lost in translation, but what you described includes a lot of misinformation and / or misunderstandings. At the mileage you listed you are past due for a typical brake system inspection. As the front brake pads wear, the pistons move out of the brake calipers to take up the slack, so to speak. That is the self-adjusting property of all disc brake systems. As those pistons gradually move out over tens of thousands of miles, brake fluid fills in behind them. That is why the fluid level goes down in the master cylinder reservoir. Eventually the low fluid switch will turn on the red "Brake" warning light. Your mechanic did not cause that. Also, not all vehicles even have that option. On those that do have it, like yours, that light can come on any time without prior warning. You have no control over where the van is when that happens, and in this case it happened while it was at the dealership. It could just as easily have happened an hour later or a day earlier.

The next valuable tidbit to understand is it is NOT proper for your mechanic to fill the reservoir to turn the light off. If I was working on your van when this happened, I would have added just a taste of new fluid, ... Enough only to turn the light off, BUT, that would be followed with this explanation of why I did not completely fill it for you. Unless there is an external leak, which would include other symptoms, the fluid level is low because the front disc brake pads are worn and will need to be replaced soon, as I already mentioned. Filling the reservoir doesn't magically fix worn brake pads. My job at that point is to strongly insist you have the brake system inspected by me or any other shop. Some even do that for free. You'll almost surely be told the brakes need to be replaced very soon.

Now for the important part. New brake linings are much thicker than the old, worn ones. To make room to fit them in, those pistons have to be pushed back into the calipers. Doing that pushes all that brake fluid behind them back up into the reservoir. If an inexperienced mechanic or unknowing do-it-yourselfer filled the reservoir previously, where is all that extra fluid going to go when the pistons are reset? The answer is it's going to overflow and make a horrendous mess on the floor, and brake fluid will eat the paint off your van. A lot of customers get angry when they find their brake fluid wasn't topped off along with the other fluids during a routine oil change, and they unfairly blame the mechanic. When questioned, my response would be, I would never do that to my customer's car, but then I'd explain why.

Your mechanic did indeed get the warning light to turn off by unplugging the low fluid switch, but you and I know doing that didn't somehow fix something. The light was on for a reason. You address that reason, not get rid of the messenger. The proper thing to do is tell you why the light is on. The next best thing is to add just a little brake fluid as long as an explanation is included. The dumbest thing is to unplug the switch.

At this point it is only fair to add one exception. That switch is on the outside of the reservoir. It is tripped by a magnet sitting on a float inside the reservoir. Once in a while that float sinks. It is fairly common then to unplug the switch to avoid having to buy a new reservoir or master cylinder. Remember, a lot of cars and trucks don't even have this option.

This sounds like you were dealing with a very inexperienced mechanic, and I really hope that is the case with the next point.

"They said oil mixed with brake fluid and made sticky, and it need to be replaced with a new master cylinder"

ABSOLUTELY WRONG ON EVERY COUNT! The hair on my neck stood up when I read that! First of all, how did oil get mixed with the brake fluid? If that is true, haul your van to the salvage yard because repairs will cost more than it is worth. There must never, never, ever be any petroleum product mixed with brake fluid. That includes engine oil, transmission fluid, power steering fluid, axle grease, or any type of penetrating oil. Very often the rubber bladder seal under the reservoir cap will get pulled down, and we customarily use our fingertip to pop it back into the cap when we have that cap off. Experienced mechanics like myself will even wash our hands with soap and water before doing that to avoid getting fingerprint grease on that seal.

All rubber parts used in brake hydraulic systems are compatible with brake fluid which is a glycol product, but petroleum products will make them swell up and get soft and mushy. Every year I did a demonstration for my students where I had two beakers filled halfway with fresh clean brake fluid. I dropped a new rubber wheel cylinder lip seal into each one, then I added a single drop of power steering fluid to one of them. By the end of the week the contaminated seal grew by about 10 percent. Four of the same type of seals are used in your master cylinder. With similar contamination, those seals will grow past the fluid return ports and block them. The front disc brakes will drag due to some fluid being trapped and unable to release back into the reservoir. That makes them get real hot, which causes the fluid to expand. Since the fluid is trapped, expanding makes the pressure go up so the brakes apply even harder. Eventually the vehicle won't even move regardless how hard you press the accelerator.

What you absolutely must understand is your mechanic is wrong when he said you need a new master cylinder. What you need is EVERY rubber part that contacts brake fluid. There is no acceptable shortcut such as replacing just the master cylinder. That oil contamination circulates throughout the entire brake hydraulic system and will affect every part that has a rubber part inside it. If every part except one is replaced, the contamination will leach out of that one remaining part and recontaminate all the new parts, and you'll have to start all over.

There are rubber seals, o-rings, or other parts in the front calipers, rear wheel cylinders, master cylinder, four rubber flex hoses, combination valve under the master cylinder, and height-sensing proportioning valve that most minivans and many trucks use. All of these parts must be removed, then the steel lines must be flushed with brake parts cleaning chemicals, and dried, then the new parts can be installed. Given the age of your van, if you live where they throw a pound of road salt on an ounce of snow, the steel lines will be rusted to some parts and will break, so they have to be replaced too. On a good day to replace all these parts will take an entire day. At $100.00 per hour just for labor, and a few hundred dollars for parts, you can see this bill will add up pretty quickly. If your van has anti-lock brakes, one of GM's systems uses a rather nice and inexpensive hydraulic controller, but it too has seals and o-rings so it will have to be replaced. That's another few hundred dollars and a lot more labor.

I personally have been involved with four cars with contaminated brake fluid. One went straight to the salvage yard. One involved a lawsuit and an $1800.00 repair bill. I repaired the other two, and they were big ordeals.

If this truly did happen to your van, you'll want to find out who is responsible to hopefully hold them accountable. The symptoms, including a high and overly hard brake pedal, and sticking brakes, will take roughly three or four days to perhaps as much as two weeks to show up once the fluid was contaminated.

To stress how easily this can happen, there was a whole rash of complaints in California in the mid '80s, all involving one mass merchandiser's shop. Some mechanics like to "pressure bleed" the brake hydraulic system when necessary with a pressurized ball that holds about three gallons of brake fluid. About a dozen customers came back with problems a week after having brake jobs done, and who knows how many more went to other shops. What they traced it to was a new kid with no training took a long plastic funnel to fill that "bleeder ball" with fresh clean fluid from a new five-gallon container. That is normal procedure. What is not acceptable is that funnel was used previously for engine oil. The kid wiped the funnel clean with a rag, then used it for the brake fluid. Just that little film of oil residue cost the company many thousands of dollars in repairs, and a major hit to their reputation.

I don't know how your mechanic determined your brake fluid was "sticky". I've never heard it described like that before, but if you start having symptoms within about a week, I'd be suspicious. At the very least you will want to speak face-to-face with the service manager about this right away. You want him to be aware of your conversation with the mechanic before symptoms develop, otherwise he will rightfully assume the fault lies with someone else and you're just trying to get someone else to take the blame and pay the bill. We see that all too often anyway. Ethical service managers are going to take this very seriously, even if the mechanic's comments and warnings prove to be unwarranted.

Be aware that for things this serious, the service advisers who write up the paperwork for your appointments won't have the authority to make decisions or offer remedies without at least discussing it with their manager first. I'd be very surprised if your service adviser told his manager about this and he didn't drop everything and come running to handle this personally. Remember, this could be a lot to do about nothing if all you need is a normal maintenance brake job, but if an employee contaminated your brake fluid by mistake, that manager is going to get it fixed. If it was contaminated on purpose to drum up business, that mechanic will surely be fired.

While I'm at it, I should point out a few related details. The red "Brake" warning light can be turned on by up to three totally different switches and reasons. The most common one by far is the low fluid light due to the need for a normal brake job. It can also be turned on due to a parking brake pedal that isn't retracting fully for any of a few different reasons. The third switch is the "pressure-differential" switch. All cars and trucks have two totally independent brake hydraulic systems so you'll have half of your brakes if one system has a leak or other problem. When one system can't build pressure when you press the brake pedal, that switch trips to warn you. There will be other symptoms too. Unplugging this switch leaves the mechanic and the shop owner open to a lawsuit if it results in a crash.

Finally, if the brake fluid really is contaminated, a good clue is that rubber bladder seal under the reservoir's cap. That will be blown up and mushy, and you usually won't be able to get it to pop back into place. As the front brakes wear and brake fluid is drawn down to fill in behind the calipers' pistons, vacuum pulls that seal out of the cap. That is perfectly normal, but it should snap back into the cap when you poke it with your finger.

Hold on. Why do you want to replace the master cylinder? What symptom do you hope to solve?

I guess I'm still missing something. If your brakes are working properly and the only symptom is the "low brake fluid" light is on, you don't have to replace the master cylinder for that. Just fix the switch. If the float sunk, you may be able to find a good used one at a salvage yard. If you can't get the float out, just replace the reservoir.

From what I understand, this is the same as saying your mechanic wants to replace your engine because the spark plugs are worn out. He is recommending the wrong service.

You're changing the story now so I'm as confused as you are. If you have a spongy brake pedal, that suggests the master cylinder could be starting to fail or it could mean the brake fluid is contaminated with a petroleum product. Contamination would agree with what the mechanic said about oil in the fluid, but how did it get there? Someone had to put it there. To fix that you MUST replace everything in the entire brake system that has rubber parts that contact the brake fluid. That contamination will go throughout the entire system and contaminate every rubber part. If you only replace the master cylinder, it is going to be recontaminated by all the other parts and the brake fluid.

If the only problem you're having is the warning light, that is the only thing to address. Replace a defective switch, replace the float with the magnet that activates that switch, or at least just add a little brake fluid. Have the front brakes inspected to see how worn they are.

Brake fluid is supposed to go from the reservoir into the master cylinder each time you press the brake pedal. The fluid returns from the wheels when you release the brake pedal and goes through the master cylinder and back up into the reservoir. It is normal for it to mix back and forth so don't worry about that.

I think my best recommendation is to get a second opinion at another shop. Do not tell them the first mechanic said you need a new master cylinder. Let them figure that out for themselves without being swayed by someone elses opinion. Tell them the brake pedal doesn't feel right. If they find the brake fluid is contaminated, that takes one to two weeks to show up, so figure out where the van was worked on during that time, and who caused it.

Remember, if the brake fluid is contaminated, you must replace ALL the rubber parts that contact that fluid, and that is going to be very expensive.

If the brake fluid is not contaminated, it is okay to replace only the master cylinder if that is what's needed.

I don't have a good answer for you. There could be one angry employee in the shop, and that person should be brought to the attention of the shop owner. No owner wants to risk his shop's reputation on the actions of one person, so if that mechanic has been caught before, he will likely be fired.

There's always two sides to every story and I've seen numerous cases where the mechanic did nothing wrong but there was real ineffective communication between the customer, the mechanic, and the service adviser in the middle, and that led to undeserved mistrust.

As far as another lawsuit, you'd have to prove where any damage was done and that will be very hard to do. I'd start with that conversation with the shop owner and see if that brings any satisfaction.

I'm not in favor of lawsuits, but I will never defend a dishonest mechanic or shop owner. As I said, there's always two sides to every story. When a car owner has asked me to explain why they were charged for something or why something was done to their car, at least 95 percent of misunderstandings were due to poor communication, unreasonable expectations, and things like that. I very seldom found an intent to defraud, however, that still leaves five percent things I can't explain as being fair. In my city we have over a dozen new-car dealers and about 100 independent repair shops. Out of all those shops, only one new-car dealer and one independent shop are well-known to be avoided because of their dishonesty. Unfortunately, it's those two shops that give the entire industry a bad reputation.