Originally Posted by Jim M.

The ABS light (at least on a 928) does not require the hammer to reset it. I think Randy is thinking of the air bag light. Most likly a relay problem. The system is very reliable, if the ABS goes off due to a system failure, braking reverts to non-ABS braking. There are several reasons for an ABS warning light. It can be corrosion at connection points, a bad relay 928 615 124 01 on the fuse panel. Using an insulated jumper wire you can bypass the relay by plugging two spade terminals into the slots on the relay board, that correspond to pins 30-87. Be sure to identify the correct slots. Open or short circuits in the speed sensors, speed sensors that have too much metallic crud in them or on the tone ring. To be functional the ABS needs to know the speed of each wheel so if any of the sensors, connections or wires fails it shuts off and triggers the warning light. The sensors are A/C voltage generators that create a sine wave output, usually somewhere around +/- 1 or 2 volts, when the teeth of the sensor ring pass the sensor. There are two electrical tests for the sensors; a continuity test with an Ohmmeter, and a comparison of the sine waves with a scope. The problem is much more likely to be faulty connections than faulty sensors. The ABS control module compares the sine waves to see if a wheel is locking. Malfunction in the ABS valve body. The ABS light should come on when starting and go off after the few seconds of self-testing. If the ABS light stays on then it’s more likely a hardware failure than a signal loss from a sensor. Start with the ABS relay. If the light goes off, but lights again within a few moments of moving off, it indicates a sensor which passes the start-up test is now failing to send an adequate signal. If ABS warning comes on after car is in motion, then there's a differential/non signal sent to the ABS brain so the sensors/connectors may be the problem. Check the sensor connections at the wheels, a black 2" long cylinder. This could be dirt in the ABS sensor area or a flaky connection. They get loose or installed in the wrong hole (3 holes, wear sensor, ABS, and RDK). Inspect the cables for deterioration and shorts from the connector to the chassis. While the ABS light stays on, the ABS module is not operating at all, but normal brake pressure will still be applied from the brake pedal. There are two relays mounted on top of the ABS unit in the LH front fender, under a cover, behind the splash shield, partially visible from under the hood, near the power steering reservoir. The system goes active at about 35 mph. The ABS control module needs to see relatively clean pulse signals from each of the sensors. If the signal from one wheel drops out, the system will turn on the ABS light and the system will shut down. Removing ABS relay will disable ABS circuit; I drove like that with no brake loss, waiting on my new relay.

Jim Mayzurk
93 GTS 5-spd

Originally Posted by davek9

Hi, you can check the sensor output (and wiring all the way to the ABS control unit under the dash,
Locate the unit and pull off the connector that has the wheel sensor wires going in the the controller.
The workshop manual gives the pin-outs for each wheel at the connector.

You can use a Volt meter if you don't have a scope, spin each wheel all should be about the same.

There are cheep/Free PC-Scope programs that can turn a Notebook into an O Scope using the sound card Mic Inputs (L&R) for probes,
Hardest part is building a voltage divider to step down the 12v to go into the Notebook (it's not really hard to build).

Originally Posted by davek9

Hi, you can check the sensor output (and wiring all the way to the ABS control unit under the dash,
Locate the unit and pull off the connector that has the wheel sensor wires going in the the controller.
The workshop manual gives the pin-outs for each wheel at the connector.

You can use a Volt meter if you don't have a scope, spin each wheel all should be about the same.

There are cheep/Free PC-Scope programs that can turn a Notebook into an O Scope using the sound card Mic Inputs (L&R) for probes,
Hardest part is building a voltage divider to step down the 12v to go into the Notebook (it's not really hard to build).

Originally Posted by Mrmerlin

look in the spare tire well it could be a loose plug ,
all the wires from the transmission and brakes and ABS come through the spare tire well.

Originally Posted by Christopher Zach

Not from the ABS. I had the same problem as many of the people in this thread of yore, and it came to the wires to the ABS were dragging on the rear axles and faulting to ground. That's why it comes on then off when starting, then comes on as soon as you move.

In my case I had to replace every one of the grommets that hold the ABS and brake pad wires all around the car. Bit of a pain, but do-able as they were all rotted out in my case.