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Join Date: Oct 2006
Location: Laguna Vista
Posts: 1,271
Brake sensors

I was looking at the these, and found a lot of contradictory info on the web. So Here is a little write up about them. Please refer to the diagram below:



The system functions as follows:
The electronics in the car want's to see a close loop of all 4 sensors conducting.
The flow goes from 6 to 7 in the instrument cluster (or 7 to 6 if you prefer, not relevant). As long as the all the sensors are conducting the brake pad light in the instrument cluster stays off.
When the pad wears down the rotor will abrade/wear the the sensor and cause its internal connection to open. At that point the the electronics in the instrument cluster will turn the brake pad light on.

Note : Once the pad light is on it will not go off even if the contact is made whole again till the car is turned off. The circuit will then reset and look for conductivity again.

Trouble shooting the system is pretty easy:

1. Disconnect all the sensors at the wheels. ( You will have to take the wheels off).
2. Connect the FR 2F to RL 5F. (see diagram above). The connector looks like this.



3. start the car, light should be off.
4. Disconnect the above step 2. The light should come on again. It should not go off even if you reconnect step 2.
5. Turn car off reconnect step 2. Start car the light should be off.

You can trouble shoot individual sensors with a meter, They should have low around 0 ohm across them, if more than 10 ohms or so the sensor is bad or about to be bad.
They should be pretty well one way or other open or fully conducting.

If your sensors are good but the step 2 above does not produce a "good" condition the its time to trace the wires between sensors...warning is a PITA.

check for conductivity between FR 1M and FL 3F.
check for conductivity between RR 8M and RL 6M.
check for conductivity between FL 4M and RR 7F.

If any of them are not connected chase as required.
If they are good time to chase to the instrument cluster.

Remember to clean the connectors with alcohol and a tooth brush before reconnecting them.
Sox
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"Little problems always come back and bring bigger friends with them".
1986 951"MADDOG" black with maroon interior
All stock with shimmed WG
Old 08-27-2018, 02:10 PM
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944 S2
 
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Location: Middle of Ohio
Posts: 227
Thatís very useful, thanks!
I changed my pads and put on new sensors and I canít seem to figure out whatís wrong (light wonít go off).
I have an S2, but the connector doesnít look like the one you have pictured.
Old 09-02-2018, 04:36 PM
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944 S2
 
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I think I see you have the early sensor pictured. My problem is with the new sensor. I canít identify M for F. They look the same! Thoughts?
Old 09-02-2018, 04:46 PM
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Use a meter to figure out which terminal goes to which...the M/F is not relevant per say.
just make sure you have the connectivity shown in the above diagram.
Quick check, jumper all 4 connectors terminals to each other, (on each connector). So the the 2 points in your picture would be connected together (on the car side not the pad side), the light should go out. If not you have a open some where in your wires.
Sox
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"Little problems always come back and bring bigger friends with them".
1986 951"MADDOG" black with maroon interior
All stock with shimmed WG
Old 09-03-2018, 09:01 AM
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944 S2
 
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Location: Middle of Ohio
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Problem solved!
I was determined to figure this out once and for all and wasnt going to lower the car off the jack stand until I got it.
Turned out all the connections were fine, but a good cleaning of the grounds At the connector by the transmission did the trick. Cleaned all the other at each wheel too.

Old 09-09-2018, 05:33 PM
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Glad it worked .
Sox
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"Little problems always come back and bring bigger friends with them".
1986 951"MADDOG" black with maroon interior
All stock with shimmed WG
Old 09-09-2018, 08:38 PM
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