diagnosing ABS problem
12-30-2009, 04:50 AM
#1
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diagnosing ABS problem
My ABS light and main warning light is on immediately on starting the car and remains on.
So far I have tested the resistance of the wheel sensors from the connector to the ABS control unit as described by Sysgen in another thread that I found (
Sysgen). This test checked out fine.
Was thinking about jumping the ABS relay G20 to see if that might be the problem. Can I break anything doing this or is there a better way to test this relay?
https://rennlist.com/forums/924-931-...ferrerid=10354
So far I have tested the resistance of the wheel sensors from the connector to the ABS control unit as described by Sysgen in another thread that I found (
Sysgen). This test checked out fine.Was thinking about jumping the ABS relay G20 to see if that might be the problem. Can I break anything doing this or is there a better way to test this relay?
https://rennlist.com/forums/924-931-...ferrerid=10354
I'm sharing my experience in fixing my ABS problem so as to help others that may have the same problem.
The ____!____ light was comming on after the car started moving. So right away that told me that the ABS control unit was ok and that the problem was with the speed sensors. But which one and why?
To easily find which one I did the following:
Disconnect the connector on the ABS control unit located on the passenger side, just to the right of the glove box by removing the two small screws circled in the first image.
Press the small ears circled on image2 to remove the connector. You end up with the connector on image 3.
Using an ohmmeter you should be mesuring ~1000ohm on each speed sensor.
Front Right, PIN 11 and 21
Front Left, PIN 4 and 6
Rear Right, PIN 24 and 26
Rear Left, PIN 8 and 9
In my case, the rear right, (which by the way is to your right sitting in the car), was mesuring 0 ohm, meaning that either the cable was cut somewhere or something was not connected correctly. it was the small connector below the rear brakes that connects the brake pads sensor and the ABS speed sensor, the cable was not pushed in correctly.
This procedure allowed me to find the problem in around 15 minutes, without having to remove every wheels
Stephane, '90 S2
The ____!____ light was comming on after the car started moving. So right away that told me that the ABS control unit was ok and that the problem was with the speed sensors. But which one and why?
To easily find which one I did the following:
Disconnect the connector on the ABS control unit located on the passenger side, just to the right of the glove box by removing the two small screws circled in the first image.
Press the small ears circled on image2 to remove the connector. You end up with the connector on image 3.
Using an ohmmeter you should be mesuring ~1000ohm on each speed sensor.
Front Right, PIN 11 and 21
Front Left, PIN 4 and 6
Rear Right, PIN 24 and 26
Rear Left, PIN 8 and 9
In my case, the rear right, (which by the way is to your right sitting in the car), was mesuring 0 ohm, meaning that either the cable was cut somewhere or something was not connected correctly. it was the small connector below the rear brakes that connects the brake pads sensor and the ABS speed sensor, the cable was not pushed in correctly.
This procedure allowed me to find the problem in around 15 minutes, without having to remove every wheels
Stephane, '90 S2
12-30-2009, 05:41 AM
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I went ahead and jumpered 30 and 87 on the ABS relay. On putting the relay back in, immediately i heard a click sound inside the RHS fender. This is the same sound I hear without the jumper when turning the ignition to the second position, so I think the ABS relay is working. Maybe this sound is the solenoid on the hydraulic unit.
Will check out the relays on the hydraulic unit next I guess.
here's the schematic from the manuals:
Will check out the relays on the hydraulic unit next I guess.
here's the schematic from the manuals:
Last edited by hally; 12-30-2009 at 06:19 AM.
12-30-2009, 10:03 AM
#5
Burning Brakes
The alternator on my car is not that strong. I have noticed that if the batterry/charging voltage is low the ABS doesn't like it and the warning light comes on.
The ABS computer is fairly easy to get to in the passenger footwell. I would check the plug and make sure its clean and dry and re-seat it. Also check the grounds which are in the same area. There are also grounds on the pump mounting bracket and under the dash on the drivers side.
I have spare computers and pumps which you can always try by substitution if your not finding anything.
The ABS computer is fairly easy to get to in the passenger footwell. I would check the plug and make sure its clean and dry and re-seat it. Also check the grounds which are in the same area. There are also grounds on the pump mounting bracket and under the dash on the drivers side.
I have spare computers and pumps which you can always try by substitution if your not finding anything.
12-30-2009, 10:33 AM
#6
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If the warning comes on as soon as the car is started, its most likely not a bad sensor, as the ABS brain wont identify or display a fault with the sensors until the car moves and it get irregular or non-matching signals from the sensors.
I would check power to the ABS brain and Hydraulic unit (confirm its not a bad relay), then check the brain itself and pump.
I would check power to the ABS brain and Hydraulic unit (confirm its not a bad relay), then check the brain itself and pump.
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12-30-2009, 02:27 PM
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My ABS light and main warning light is on immediately on starting the car and remains on.
So far I have tested the resistance of the wheel sensors from the connector to the ABS control unit as described by Sysgen in another thread that I found ( Sysgen). This test checked out fine.
Was thinking about jumping the ABS relay G20 to see if that might be the problem. Can I break anything doing this or is there a better way to test this relay?
https://rennlist.com/forums/924-931-...ferrerid=10354
So far I have tested the resistance of the wheel sensors from the connector to the ABS control unit as described by Sysgen in another thread that I found (
Sysgen). This test checked out fine.Was thinking about jumping the ABS relay G20 to see if that might be the problem. Can I break anything doing this or is there a better way to test this relay?
https://rennlist.com/forums/924-931-...ferrerid=10354
on edit, had my car repainted earlier in the year and after a few rain showers my rear left light had filled with water due to plugged drainage tubes...this why it faulted
10-28-2019, 12:56 AM
#10
Abs light always on
As per Mr. Hally diagram of abs system, how can I identify that my abs control unit is faulty.... Is it abs control unit which supplies power to hydraulic unit solenoids & relay... Anyone here who can help me understand the wiring diagram...?
I mean that the primary circuit of relays(pump & solenoids) is connected to control unit directly & there are so many power line(12volt) to control unit, don't know why so many power line.......
I get ignition power at terminal 1, 27, 28 with the control unit connector disconnected & ground at 10,20, 34...
Thanks
I mean that the primary circuit of relays(pump & solenoids) is connected to control unit directly & there are so many power line(12volt) to control unit, don't know why so many power line.......
I get ignition power at terminal 1, 27, 28 with the control unit connector disconnected & ground at 10,20, 34...
Thanks
