ABS question

RLambert · Jan 9, 2009

Hi everyone.

The ABS light was on my 89 C2 when I bought it. The garage that sold it to me said it had only just come on and it was probably was due to lack of use. They had just MOT'd it and it had done zero miles since so a bit iffy !

Anyway, I found a broken brown wire on one of the front wheel sensors so soldered it back on. If this had fixed the problem should the ABS system reset itself or does it need to be done with some 'special' and no doubt expensive equipment ?

The ABS still isn't working and I get that really annoying and loud warning beep everytime I switch on the ignition.

Thanks
Richard

RLambert · Jan 13, 2009

Anyone any ideas ?

Steve Brookes · Jan 13, 2009

This is only a guess but since you've had no reply I'll suggest it anyway.

You could try disconnecting the earth lead for a minute to see if that resets it (this works on models like Boxsters). If it doesn't (and I suspect it won't) you'll probably need a garage to clear the fault with a Bosch 'Hammer'. If that still doesn't do it you may have to look at getting a new sensor and putting it in.

Hope that will be of some help.

chrism964 · Jan 13, 2009

This is referenced directly from Adrian Streather's book. Porsche 911 Enthusiast's Companion (Tm). Bentley Publishing ISBN 0-8376-0293-9. Pages 406 and 407

Page 406 is for Carrera 2 Turbo-look Cabriolet, American Roadster, Carrera RS, Carrera Cup and turbo series brake troubleshooting. (May not apply to your C2 as this has a vacuum booster not the hydraulic booster but I've typed it out anyway)

"Brake pressure warning light on, warning horn sounding -

Brake pressure has reached 102 bar and is falling. Stop driving immediately. Common reasons for this failure are listed in order of priority:
Seal between pressure switch and hydraulic pump has failed and brake fluid is being pumped out into the luggage compartment. The failure is obvious and requires immediate action. Plus cleaning up.
Pressure switch has failed and must be tested using brake boost pressure test equipment: or simply replaced.
Hydraulic pump has failed. This is easily evident. The brake warning and warning horn are on, pump should be running. If not, check fuse 15 and relay R51. If okay, pump has failed. Normally pump will show evidence of overheating.
Hydraulic accumulator has failed. To test this, specialised equipment is required."

Page 407 is for the ABS.

".... there is only one warning light associated with ABS failure: The ABS warning light. It will normally only illuminate under the following conditions after engine start.

- ABS warning light goes out after 2.5-5 seconds and immediately comes back on with a warning horn. This indicates that the ABS control unit has failed or an ABS solenoid valve inside the ABS hydraulic has short-circuited.

- ABS warning light goes out after 2.5-5 seconds and stays out until the 964 has reached 7kph (4mph) plus a few seconds and then comes on again. This indicates that there is a wheel speed sensor problem or the ABS return pump in the ABS hydraulic unit has failed. "

HTH

Chris.