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Hi, Joe.
I've got Saab Factory Manual ABS Braking System 5:2, Bentley book and I've looked thru Towsend's site (check the link below). Unfortunately Factory manual says nothing about self-diagnostic functionality so we have to go with Towsend and Bentley.
Test connector (2-pin socket): it should be either behind ABS hydraulic unit or under the rear seat not too far away from ABS ECU.
Symptoms part... (longish, sorry)
I often notice that people don't understand that there're two almost independent systems there: power-assisted brakes and anti-lock add-on. You can take the ABS ECU out of the car and still have power-assisted brakes (but if you take the hydraulic unit out then you'll have nether brakes no anti-lock functionality since there will be nothing to get locked and anti-locked, lol).
All you need for brakes to be power-assisted is:
- electrical power from battery and-or alternator (that goes thru some fuses and relays)
- working DC-pump
- healthy hydraulic pressure accumulator (aka bomb, pear, accumulator)
- pressure sensor that turns the pump on and off
- brake fluid, wiring, lines, pads, rotors, etc
That's it! You don't need the level sensor that senses the brake fluid level in the reservoir, you don't need ABS ECU, valve block or anything else. The ECU only helps (in the design implemented in C900) to work with the lights in the instrument cluster: if the brake fluid level goes too low then "Brake fluid" or "(!)" light comes on. It also senses the system pressure and gets the light on if it drops below a certain value.
The ABS part works with wheel sensors, modulating valves and other staff. It can be considered to be a sorta add-on to get anti-lock functionality. It can bring ABS light on in a case of wheel sensor or valve failure. The ECU also shuts the ABS functionality down if the brake fluid level gets too low.
From what I've studied from your post I would suspect the following parts:
- brake fluid pump. If it's overheated then it might be unable to pump up the brake fluid to an appropriate pressure.
- valves. 90% said about the pump goes here as well.
- ABS ECU. I've heard some stories about other makes that had ABS ECU placed not in an appropriate place thus it was subjected to heat and once overheated can go crazy
So if I were you I would start with the brake fluid level check then I'd go with DC and resistance checks for pressure sensor, level sender, valves. Then I would check if the ECU gets heated... I don't know what can be the source of a heat there, maybe some exhaust parts? Obviously I'd pull ABS codes out since if an ECU (fuel, ignition, ABS or whatsoever) is trying to tell me something then it's worth listening to it.
I bet it will probably be the level or pressure sensor although to be honest I don't quite understand you saying "pressing the pedal feels as if the ABS is pulsing" - if you get both lights on and press the brake pedal and it flutters or pulsates then... It may be the ECU that went south or just was overheated.
And the most important part: always replace the brake fluid every two years or 40K miles whatever comes first and don't rely on others saying they never heard of this rule and it was quite ok of them. That's about yours and others safety, READ THE MANUAL. Old brake fluid having too much humidity absorbed can also cause the issue you describe to happen.
Zig
posted by 91.77.159...
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