ANTI-LOCK BRAKE SYSTEM TROUBLESHOOTING AND TESTING - CONTINUED
GENERAL INFORMATION - CONTINUED
The ECU receives and processes signals from the wheel speed sensors. When the ECU detects a wheel lockup, the unit
activates the appropriate modulator valve, and air pressure is controlled. In the event of a malfunction in the system, the
ABS in the affected wheel(s) is disabled; that wheel still has normal brakes. The other wheels keep the ABS function.
An ABS warning lamp lets the driver know the status of the system. If the ECU senses a fault during normal vehicle
operation, the ABS warning lamp will come on. This lamp is also used to display blink code diagnostics.
ABS WARNING LAMP
The ABS warning lamp works as shown in Table 1. If the ECU senses a fault during normal vehicle operation, the ABS
warning lamp will come on and stay on.
Table 1. Warning Lamp Operation.
ABS MODULATOR VALVES
Modulator valves control the air pressure to each affected brake during an ABS function.
To make sure the ABS valves are working, listen to them as follows:
Turn on the ignition.
Wait for the ABS light.
The valves will cycle in 1-2-3-4 order, then diagonally in 1-2 and 3-4 order.
Listen for the valves to cycle, one by one, then together diagonally (Figure 2).
WHAT YOU DO
WHAT IT MEANS
Turn the ignition on.
The ABS lamp comes on momentarily for a bulb check,
then goes out.
The system is okay.
The ABS lamp does not go out at ignition.
If the lamp goes out when the vehicle is
driven above 4 mph (6 km/h), the system
If the lamp does not go out at speeds above
4 mph (6 km/h), the ECU senses a fault in
the ABS system.