Car Brake Warning Light help

[Oreo]

Quite a lot of background info so bare with me.

About a month back, my brake warning light came on, we looked at the front pads and they were about 1cm thick which is fine. Checked the rear ones, and the discs were worn down unevenly and the pads were only 5 or 6mm thick, so I booked it in for rear pads and rear discs to be be replaced. I had already bought some replacement pads for the rear so they only had to fit them, and supply the discs. Anyway, half way through the day the garage rings and says "We've took the front wheels and brakes apart, the pads you supplied do not fit" I told them that is because they are rear pads and I had asked for the rear pads and discs to be replaced, and I had a receipt from them to prove it when I booked it in. Then he was like, "Oh sorry.. we'll put it all back together and then fit the rears as asked" so 6 hours later I pick the car up, have a quick check and they have indeed fitted rear pads and discs, all working well as far as I could tell.

However, I started the car up and the brake light was still on. I attributed this to them just being refitted and it'll take a few miles to reset or whatever, I had read this on the web. I don't know if its a load of **** or not but whatever, I didn't have the money to take it back and pay for something else to be fixed as well. So here I am 4 weeks later, my brake warning light is still on. Despite the brakes feeling and working seemingly fine, I figure I need to sort the problem because my car goes in for its MOT in 10 days and if the brake warning light is still on it will fail. So I plug in an OBD2 Scan diagnostics to my car, it scans for error codes, but only picks up the one I already know about (Engine management error due to failure of an exhaust gas purifier thing which removes emissions, which has no real impact on the car so we just leave it and reset it each time for the MOT so it doesn't fail). I was puzzled as to why my OBD2 diagnostics scanner does not report the brake warning error, so all their is left to do now is to take all the ******* wheels off and look for myself. Which I have now done.

All the pads are thick, the discs are thick with even wear, all the pipes and cables appear to plugged in correctly. I wiggled them around a little and made sure they were connected nice and firm, but still the brake warning light stayed on.

I am at a total loss to what the error could be. Maybe the error was not even to do with the pads in the first place as I can't see any brake wear sensor on the rear brakes.. or maybe the garage was ****ed off because they had to basically do the job again, so they thought they would **** it up for me so I have to come back.. or maybe it is a problem with the front brakes all along. I really have no clue anymore and I have no idea how to do more advanced **** like bleed brake fluid or whatever.

Any thoughts or opinions would be appreciated.

 

[PP Mguire]

Unplug the negative cable from your battery and leave it unplugged for say, 30 minutes to be safe. Plug it back in and drive around about 10 miles or so. If your brake light still comes on something else is still wrong.

Also, when you do your brakes if you have 4 wheel disc you always do all 4 and bleed the calipers. That way, all 4 wear the same, and bleeding means that there is no extra pressure being sent to each one wheel.

For future reference if one side (pads) is lower than the other that means more pressure is being sent to that caliper. If pads are uneven that means your rotor (disc) needs to be replaced as well as the pads.

 

[Oreo]

Thanks, but I just googled disconnecting the battery, and while it may work people complain of it ****ing things up like electric windows, fuel cap not locking, radio needs resetting, ESC being turned off, and various other things.. sounds to risky for me to try

 

[PP Mguire]

Radio reset yes, never heard of the rest before. The unplugging of the negative on the batt stops power being sent to all electrical items, including the ECU which is throwing the code. That is why I said do that. It will take the code off, and if it comes back on then that means something is still triggering the code to be active. The only other way is to take it to a shop that has the device to clear the code.

 

[Oreo]

Well I guess I could give it a go and hope it doesn't screw up anything else.

 

[PP Mguire]

Well I guess I could give it a go and hope it doesn't screw up anything else.

I really don't see how it can screw up basic electronic things that aren't powered by a computer. Like the windows for instance. It is a button that makes a connection to make the window go up or down. Gas door lock, not so sure about. I don't have one of those. Radio, yes. It loses power to the internal memory losing your presets.

 

[GhOsT1321]

I would try bleeding the braking system, but I am unsure if the braking pressure is monitored or not. If you have all disk brakes, you may have a bleeder bolt on the calipers, which makes bleeding very easy.
Just to be sure it's not something simple: Pop the hood open and take the brake fluid cap off while the car is off. Make sure that a piece of plastic is floating at the top and not stuck at the bottom. I once had that thing get stuck after closing my hood, and I had a brake light constantly on until my dad took a screw driver and popped up the piece of plastic.
Make sure not to get any debris into the brake fluid, and know that brake fluid is corrosive.

I would never take my car to any shop for simple brake work, especially with disk brakes.
Too many dishonest mechanics where I live.

 

[PP Mguire]

I would try bleeding the braking system, but I am unsure if the braking pressure is monitored or not. If you have all disk brakes, you may have a bleeder bolt on the calipers, which makes bleeding very easy.
Just to be sure it's not something simple: Pop the hood open and take the brake fluid cap off while the car is off. Make sure that a piece of plastic is floating at the top and not stuck at the bottom. I once had that thing get stuck after closing my hood, and I had a brake light constantly on until my dad took a screw driver and popped up the piece of plastic.
Make sure not to get any debris into the brake fluid, and know that brake fluid is corrosive.

I would never take my car to any shop for simple brake work, especially with disk brakes.
Too many dishonest mechanics where I live.

Same. I might have to though. I can't get my caliper bolts loose

 

[Oreo]

I really don't see how it can screw up basic electronic things that aren't powered by a computer. Like the windows for instance. It is a button that makes a connection to make the window go up or down. Gas door lock, not so sure about. I don't have one of those. Radio, yes. It loses power to the internal memory losing your presets.

I would try bleeding the braking system, but I am unsure if the braking pressure is monitored or not. If you have all disk brakes, you may have a bleeder bolt on the calipers, which makes bleeding very easy.
Just to be sure it's not something simple: Pop the hood open and take the brake fluid cap off while the car is off. Make sure that a piece of plastic is floating at the top and not stuck at the bottom. I once had that thing get stuck after closing my hood, and I had a brake light constantly on until my dad took a screw driver and popped up the piece of plastic.
Make sure not to get any debris into the brake fluid, and know that brake fluid is corrosive.

I would never take my car to any shop for simple brake work, especially with disk brakes.
Too many dishonest mechanics where I live.

Well my dad just got home who knows a lot more about cars and the wiring and stuff. He took a look and we found out only the front left brake has a pad wear sensor, he tested the sensor somehow and figured it was good, but he tested the wiring going to the sensor and as far as he could tell it was dead. So we think the wiring is damaged somehow and some wear, we tried to find wear the wiring routed up into the engine bay but it was a ******* and even after 30 minutes searching we couldn't find it.

So we are going to book it in to our local mechanic who seems pretty reliable, they have fixed my car, sisters and mums in the past.. whether they added extra cost and parts on we will never know but they definitely did a proper job fixing the issues. The woman who owns it is very nice and we speak to her regularly as she lives close by in our village.. so you would hope if she is kind she wouldn't run a business that rips people off but who knows.

I will try what you said first though Ghost.

 

[C0RR0SIVE]

The typical BRAKE light comes on in only TWO scenarios, unless you have a more exotic car. Low fluid level being sensed, or your E-Brake has been pulled.

Check your fluid level, it is possible when they compressed your calipers and didn't do a proper bleed, that excess fluid left the reservoir, when applying pressure, the remaining drops below your sensor and trips the light.

Air in the lines will NOT cause the light to come on...

The reason for un-even wear can be:
Crappy pad materials, one pad for some reason is superior quality.
Un-even break in on pads
Caliper Slide pins not being cleaned and lubed up properly twice a year if drove daily.
Sticking caliper piston, some cheap pistons are made of ceramic that eventually swell up and seize.
Bad valve in the system.
Bad Master Cylinder though, shouldn't cause your type of un-even.
Bad rubber lines either ballooning, or collapsing on the inside, preventing proper fluid flow and pressures.
Air or WATER in the line. Believe it or not, water gets into the fluid much more quickly than air, because brake fluid is a "dry" liquid, and sucks moisture straight out of air.
None of this causes that light to come on honestly.

But I will say once again, check your fluid level in the reservoir. Make sure the sensor on the bottom of the res or Master Cylinder is plugged up, not corroded, or damaged. DO NOT REMOVE THE SENSOR, JUST THE PLUG, otherwise you will drain the res, and master cylinder. The "sensor" your dad is checking is most likely a hub speed sensor and NOT a pad sensor, unless again, this is an exotic or very new fancy car. Most cars, the Caliper has a metal tab that will touch the disk or drum and squeal telling you it needs serviced.

Would help GREATLY if I knew exactly what make/model/year car you was working on, maybe I could find some information on the particular system used in your car.


@PP: For future reference, 97 Lincoln Town car, the windows are in fact controlled by the computer system. A lot of cars, especially "luxury" cars, EVERYTHING goes through A computer of some form.