Check Brake fluid level.
When the ABS light is on, the brakes should revert to standard braking.
The only time ABS should invoke is when the tires are slipping as sensed by the wheel speed sensors when the wheel locks up on any of the axles.
ANTI-LOCK BRAKE SYSTEMS
Fig. 1: RWAL brake system diagram
Fig. 2:4WAL Component locations — except 1996 models
p>Fig. 3: 4WAL Component locations — 1996 models
Fig. 4: Three sensor 4WAL brake system diagram — Except 1996 models
Fig. 5: Four sensor 4WAL brake system diagram — Except 1996 models
There are two basic types of anti-lock systems available for this vehicle; a Rear Wheel Anti-Lock (RWAL) brake system and 4 Wheel Anti-Lock (4WAL) brake system. The 4WAL system has two variations; a 3 sensor system and a 4 sensor system. The 2WD vehicles will be equipped with the 3 sensor system, but the AWD vehicles can be equipped with either. The systems are easily identified by looking at the rear wheels for a sensor harness. If there is a sensor harness and thus, rear wheel sensors, it is the 4 sensor system. If the vehicle is not equipped with a harness, it is the 3 sensor system. The 4 sensor system takes it speed references from each of the wheels. The 3 sensor system takes its speed references from each of the front wheels and the vehicle speed sensor located in the transmission (2WD) or the transfer case (AWD).
The RWAL system components consist of the Vehicle Speed Sensor (VSS), the Electronic Control Unit (ECU), the isolation/dump valve and the Vehicle Speed Sensor Buffer (also known as the Digital Ratio Adapter). The ECU also receives signals from various brake switches.
The 4WAL system components consist of the Electro-Hydraulic Control Unit (ECHU) valve (also known as the Brake Pressure Modulator Valve or BPMV), the wheel speed sensors, Vehicle Speed Sensor (VSS) on 3 sensor systems and the VSS Buffer.