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Old 11-22-2002, 11:35 AM
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Join Date: Jul 2002
Posts: 197
brake pad light

I have an 89 300 se with 174,000 miles. I had just had the rear brakes replaced and the front pads have been checked. In driving the car today, when I apply the brakes(mostly hard braking) the brake light on the dash comes on. I checked the fluid level and it is ok. Today is one of the first days it has been near freezing temperatures. Since the pads were checked 2 months ago, is it possible that the temperature maybe is halfway freezing the brake fluid and allowing the sensor to think it has bad pads?
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Old 11-22-2002, 03:12 PM
haasman's Avatar
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Join Date: Jun 2001
Location: San Francisco, CA
Posts: 3,096

I have never heard of brake fluid freezing unless it had water in it.

My guess is the brake pad light is telling you exactly what it is supposed to tell you: You front pads need to be replaced.

It is not uncommon for someone to visually inspect the front pads, delcare that they still have life in them, and then a short while later have the light come on.

Why? Because the sensor is embedded roughly 1/16" from the brake pad backing pad. This is so you are warned before the metal brake pad backing starts making contact with the brake disk (rotor) ruining them but most importantly loosing your braking from that wheel.

'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)
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Old 11-22-2002, 03:16 PM
Posts: n/a
There are two brake lights. One says BRAKES and basically indicates hydraulic or parking brake problems. The other is the circle with marks around it, which indicates excessive pad wear on the front brakes.

If it is the circle with marks, you either have a wear sensor contacting the rotor, or one of the leads has shorted to ground. If the BRAKE light is coming on, you have a hydraulic situation or possibly the switch on the parking brake foot pedal assembly.

Good luck,
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Old 11-22-2002, 03:40 PM
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Join Date: Jul 2002
Posts: 197
brake pad light

thanks for the info. The funny thing is that the light does not come on every single time. It almost seems like there maybe a malfunction in the light itself or one of the sensors. I will, of course, have the front brakes checked I have had them checked previously by more than one mechanic, but like you say, that does not always mean there ok. It's funny though that today is the first time the light has come on when the temp is as cold as it is. Thanks.
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Old 11-22-2002, 08:43 PM
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Join Date: Jul 1999
Location: CT, USA
Posts: 2,699
Front pads are likely cooked. When they are just beginning to run on the wear sensor, the warning light can be intermittent.

Good luck, and make sure your brake fluid is no more than 3 years old!
"If everything seems under control, you're simply not going fast enough" --Mario Andretti

1995 E500 street car
1986 Porsche 944 Turbo S track car
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Old 11-23-2002, 04:02 PM
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Join Date: Feb 2002
Location: Canton, MI
Posts: 54
I just changed my front pads. The light only came on when the rotors were cold. That is when I applied the brakes the first few times. Once I was in stop and go trafic and the rotors and pads were hot the light would not light.

I gently removed the sensors and found that indeed one of the sensors was cut and making ground. After I pulled the pads from the caliper it was obvious.

Good luck.

1994 E320
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Old 11-25-2002, 08:46 AM
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Join Date: Jul 2002
Posts: 197

The funny thing, over the weekend, I pulled the front wheels off and inspected the pads and sensors. The pads are worn, but look like they probably have at least 5k left on them. The sensors, other than being covered in brake dust looked pretty good. I unplugged them and plugged them back and put the wheels back on. The light does not come on as much and sometimes will come on while accelerating(no brakes being applied). I went ahead and order new sensors and pads and I think I will go ahead and do the job and get new pads on the front because it will only be a matter of time before I have to do it anyway. I suspect that one of the sensors is bad since it sometimes would come on with no brakes applied.

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Old 11-25-2002, 04:40 PM
Neil Richardson
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I agree with the guys. It sounds like the front pads. Have got the same problem myself. My guy looked at the car on Saturday and confirmed my suspisions. He's replacing them next saturday for me. He did give me one piece of advice though. Don't drive more than a 1,000 miles after the light comes on. The pads might be sofar run down that they won't work, or you press hard and they give.
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Old 11-25-2002, 04:57 PM
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Join Date: May 2002
Location: Mass
Posts: 1,127
The wiring to those sensors is very fragile. It would not take much for them to malfunction.

Even if they are working, don't expect the light to stay on all the time. It will only come on when it gets a good ground on the rotor.
1986 300E 5-Speed 240k mi.
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Old 12-02-2002, 09:01 AM
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Join Date: Jul 2002
Posts: 197
brake pad light

just to let everyone know, I changed the brake pads/sensors this past weekend and 2 of the sensors, the pad had worn down so far it had worn the wires down halfway. So, it was very much time to replace the pads. After installation, the light went out and has never come back on. Thanks everyone for the information.
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