"Brake" warning light is on...why ?

[radeohedca]

The Brake warning light on my 1999 Montana is lit. The owners manual says to check the brake fluid level in the reservoir and make sure the safety brake is not applied. There's plenty of fluid and the safety brake is fully released. I even checked the switch on the safety brake (makes to ground when safety brake applied) and it's fine.
Is there any other reason for the Brake warning light to come on ?

Thanks.

[LMP]

If rear brakes are drum and misadjusted, it can trig the light.
Front pads require very little pedal play as pads barely retract and have no springs. But if rear brakes require long travel, this mismatch is detected by the master cylinder . I have not had this problem with my Transport, but my other car (Kia SPortage) , from time to time, needs that I make a dozen hard stops in reverse as this cranks the adjustment, which it does not going forward, or if I just make smooth stops in reverse.
But a rear piston leak within the master cylinder is another possibility. I say rear because if it were the front, you would know from degraded braking ability. It is much less conspicuous from the rear.

[1999montana]

I agree with LMP.

With a 1999 model, the rear wheel cylinders can begin to leak due to the fact that the brake fluid has never been flushed. The wheel cylinders will actually corrode and fail for this reason.

This is due to water or moisture entering the hydraulic system. Brake fluid has an 'affinity' to attract and retain moisture in suspension. If the original fluid has been in there for 9 years, it has been in there way too long.

Our van had a problem with the adjusters not 'expanding' the shoes as they wore, and as a result at one point there was excessive pedal travel before a firm pedal was obtained. Adjusting the rear brakes eliminated this problem.

To mimic this, you can partly apply the parking brake while moving forward. If the pedal travel is reduced, it suggests that the rear adjusters need to be adjusted.

If the adjusters are seized, (sometimes happens if the brakes have not been services in a long time), no amount of panic stopping in reverse will cause them to adjust.

You'll have to take the rear drums off, take the entire assembly apart, (careful, you are fooling with asbestos so use plenty of brake cleaner and dispose of the liquid in a suitable container at a transfer station). clean and lube the rubbing points on the backing plates, clean and lube the adjusters, reassemble and then set the rear brake adjustment for a slight interference fit of the drum as a starting point.

Then a few hard stops in reverse, followed by a forward stop in between each reverse apply will set the adjusters for proper adjustment.

The brake warning light is a float in the master cylinder. It monitors the fluid level and comes on at a predetermined point.

But there may be other reasons why the light comes on, I just don't have schematic to see if there are other 'monitoring' trigger points that may trigger a warning.

Could be a wheel sensor or the ABS, but mostly likely is not.

[radeohedca]

Thanks for the reply guys.

Is the brake fluid sensor actually a float mechanism ? I assumed it was a non-mechanical electronic sensor but now that I think of it, brake fluid probably isn't such a good conductor. The reservoir is buried back under the firewall/hood sheet-metal so I can't get a good look inside. The sensor is located low on the reservoir and the fluid level is higher than the sensor so maybe I was thrown off by assuming there is enough fluid in there. It definitely isn't "topped up" so I will add more.

Speaking of the barely accessible brake fluid reservoir, how do you fill the damned thing ? Looks like I may need a turkey baster with some neoprene hose on the end of it. Any better ideas ?

BTW, I was looking at the service manual for my '97 GTP. The schematic of the Brake warning lamp circuit shows 3 inputs... The fluid level, the emergency brake and the PCM. Assuming Pontiac used similar electrics in '97 and '99, if topping up the fluid doesn't extinguish the light then it has to be a fault stored in the PCM or a problem with the PCM itself. I will find out when my wife brings the van home tonight.

Hugh.

[1999montana]

Originally Posted by radeohedca

...The sensor is located low on the reservoir and the fluid level is higher than the sensor so maybe I was thrown off by assuming there is enough fluid in there. It definitely isn't "topped up" so I will add more...
Any [better] ideas ?...BTW, I was looking at the service manual for my '97 GTP ...Assuming Pontiac used similar electronics in '97 and '99...

Hugh,

I would try taking a top from another container that has a tapered spout. Clean it first before using. I use the one from the air tool and machine oil container (minus the machine oil and traces of, of course!) plus a length of neoprene hose so you can see how much fluid is flowing into the reservoir. It's a nasty angle, but accessible if you attack it this way.

I think you may be safe assuming the schematic is very similar, the engineers don't often fix something 'that ain't broke' so it will likely map well to your van.

You need to ask yourself why the fluid went down...worn pads, worn brake shoes or a leaky wheel cylinder perhaps?

[radeohedca]

Well, I added some brake fluid. No change...the Brake warning light is still illuminated.

I pulled the plug off the brake fluid level sensor and the emergency brake pedal.
No change.

The only other input that controls the Brake warning light is the Brake control ECM so I scanned it with my scan tool but no codes show up so I'm puzzled.

[brcidd]

My wiring diagram shows the parking brake switch as an input to the Daytime Running Lights module-(located Right of the steering column, behind the IP) then that leads to the instrument cluster in parrallel to the fluid reservoir switch, AND also in parallel to the electronic brake control module/Electronic Brake Traction Control Module (located Left side of the IP, above the parking cable bracket)

I would suggest unplugging these two modules one at a time to determine the source of the ground (-) that is lighting your light on your instrument cluster

Another simple question to elimnate the parking brake switch question- Are your Daytime Running Lights (DRLs) working?

[radeohedca]

Here's the latest...
I unplugged 2 separate connectors from what looks like another proportioning valve body that is in front of the master cylinder (similar to but not to be confused with the main proportioning valve beneath the fluid reservoir) and the Brake warning light went out. I plugged one in at a time and discovered that the front one is causing the Brake warning light to come on.

Is this other valve body part of the ABS system ? Do the connectors plug into sensors or solenoids ?

Any leads based on this new infomation ?

Thanks, Hugh.

[catesja]

The assembly you are referring to is the ABS module. One set is for the front brakes, the other for the rear. Try to get up to a good speed on an open area with no other cars around, then slam the brakes and see if the ABS works or if they lock. This should also make the light come on, and may need to be rest. You can reset it with disconnecting the battery. I have found this method more reliable than a scan tool for resetting.

If the wheels lock up, then you have an ABS problem, if not then it could be a sensor on/in the valve body.

[catesja]

I am reading the repair manual now, it says that if the ABS light is out, that the ABS system should be fine, if this is the red brake light that is lit, it indicates a problem with the main braking system. It say to check fuses, electircal connectors, and vehicle speed sensors and brake light switch making sure all are tight and secure. You might also check the EBCM (Brake control module)

I would do a full system clearing of codes with the disconnection of the battery. This will clear any and all codes out. Then start the vehicle with the brake off. Then again with the brake on.

You could also try bleeding the brake system, including the ABS system.

[radeohedca]

Okay, <blush> I neglected to mention that the ABS warning light has been on for a couple of months. I suspect a bad wheel bearing and was waiting for the warmer weather to change it. (Interesting to note BTW that an OBD II scan shows no error code).

The Brake warning light, the subject of this post, just came on last week so I did not connect the two since I thought the Brake warning light was more to do with the base braking system. I now know that they may or may not be related.

First I'd like to establish what the two connectors on top of the ABS module go to ? Are they sensors or solenoids ? As I mentioned, if I unplug one of them then the Brake warning light goes out.

[catesja]

I believe they are solenoids to activate the pressure of the ABS system, they would most likely lead to the Electronic Brake Control Module (EBCM) located under the left end of the instrument panel.

What I would try first is inspecting both calipers on front, and both wheel cylinders on the rear. Then if all is good, bleed the system as follows:

Make sure the master cylinder is full. Disconnect the battery.
Your '99 right? Then you will need to start with the ABS pack rear bleeder (both are on front but one is back a little further then the other). Connect a hose and a can or fluid like you would a wheel bleeding. Have a helper press the pedal 3/4 the way down, not all the way, and hold. Close the bleeder screw and let off the pedal. Repeat until no air comes out, watching the master fluid level. Then move onto the front bleeder and repeat. If you have TCS then you must do the same to that module, if not move on to the wheel bleeding. and do the same but in this sequence: Right Rear, Left Front, Left Rear, Right Front. Wathc the master at all times to never drop to low, and make sure it is full at the end of the bleeding.
Then bleed the ABS again, but this time do so at the brake line fitting not the bleeder. Once this is all complete, test the brake system. Turn key on but not start. Press pedal, if it is har dand firm, no sponginess, then start the engine and check the pedal travel and feel. Feel ok? Great, check the master cylinder and make sure it is full and take on a road test. Are the brake lights out? Even better! If not, r the pedal is not good, then repeat the bleeding and testing again. If still not good after a second bleeding, I would say you have a module out, or a sensor of some sort.

[catesja]

I had a 2000 Venture that had an ABS light on for awhile, then it rained and poured and the next day it was out. You might try washing the engine compartment too!

[radeohedca]

How would bleeding the system correct things ? The lights are coming on right when I start the engine...the van hasn't even rolled yet so you would think it's not related to a wheel sensor.

And I don't understand why the ABS/TCS and Brake warning lights are coming on but an OBD II scan produces no DTCs ???

I'm at a loss and I feel the frustration setting in (

[catesja]

The lights will come on with the key in and on, but not running as a system check, they will also signal a system malfunction. With the engine running, the power brake system creates pressure in the system. Moving or not there is pressure if the engine is running. If the pressure is low, indicated by a spongy pedal, or a pedal that travels farther than it should. If you ever let the master get low on fluid, then air has been introduced into the system and possibly even water. This si teh reason for bleeding. Not only will the air get expelled, but the pressure will be brought back up. Youcan usually hear the ABS module release pressure when teh hood is open and the engine was just turned off.

Plus, bleeding the system, although time consuming, is a cheaper possible fix to the problem.

Wheel sensors are what tell teh ABS to function or not. If a wheel/speed sensor is not working, the ABS system won't know how to act in the event it is needed. This why you might want to test the ABS system to see if it is working, by doing the sudden hard stop going over 30 in a controlled area with no other traffic if possible.

Also, you might try getting it scanned with another scanner to determine if your scanner can get all the codes. Take it to an autoparts store that can pull codes for you. This is usually where I go first to get codes pulled, but they never can seem to clear the codes with their scanners!