EMUT performs the following functions:
- Checking wheel speed sensor inputs.
- Determination of the wheel lock tendency.
- Control of the brake system in the anti-lock braking system control mode.
- Checking the system for proper electrical operation.
The EMU constantly checks the speed of each wheel to determine the start of wheel lockup. If a wheel locking tendency is detected, the EMU instructs the appropriate valve to adjust the brake fluid pressure in some or all of the hydraulic circuits to prevent wheel lockup and provide optimal braking. The EMU continues to monitor the pressure in the individual hydraulic circuits as long as there is no tendency to block. The EMUT also constantly monitors the proper functioning of the ABS. If the EMU detects an error, it can disable the ABS function and turn on the ABS warning light on the instrument panel. The EMU also controls the display of fault codes in diagnostic mode.
Valve relay
The valve relay provides power to the electric pump and solenoids. The switch in the relay is normally open, but it closes during initialization. The relay switch remains closed for the remainder of the drive cycle until there is no DTC to allow the switch to open. If a DTC is set that requires the relay to command OFF, battery voltage is removed from the electric pump and solenoids for the remainder of the current driving cycle and the ABS cannot function. The relay is an integral part of the EMU and cannot be serviced separately.
Wheel speed sensors
A wheel speed sensor is present on each wheel. The sensors transmit information about the wheel speed to the EMU using a small alternating voltage. This voltage is generated by magnetic induction caused by the passage of the gear ring of the sensor. The amplitude and frequency of the alternating voltage are proportional to the speed of the wheel and increase with increasing speed. The signal is sent to the EMU through the interface, which can result in incorrect or noisy wheel speed sensor input. Two different types of wheel speed sensors are used for the DBC7 system.
ABS warning light (yellow)
The ABS warning light is located on the instrument cluster and illuminates when an ABS fault is detected by the EMU. The ABS warning light informs the driver that there is a condition that has caused the anti-lock braking function to turn off. If only the ABS warning light comes on, normal full power braking is present.
Below are the conditions under which the ABS warning light comes on.
ABS fault detected. As described above, the ABS warning light comes on when a fault is detected in the ABS.
Checking the instrument cluster light. When the ignition is turned on, the ABS warning light comes on for approximately 3 seconds and then turns off.
Brake warning light (red)
The red brake warning light is located on the instrument cluster and illuminates to warn the driver that the condition of the brake system may result in reduced stopping power. The lamp lights up when the parking brake is applied or partially released or when the brake fluid level switch is closed (the switch closes when the brake fluid level in the master cylinder reservoir is low). When the brake fluid level switch is closed (low level) the brake warning light stays on until the problem is corrected. Also, some fault modes in the DBC7 system will turn on a warning light to notify the driver that DDRP has been turned off.
Diagnostics
The diagnostic circuit test is an organized approach to identifying the problem caused by a malfunctioning ABS/DDRP system. The technician should begin diagnosing any ABS/DDRP malfunction with a diagnostic circuit test. The diagnostic circuit test guides the service technician to the next logical step in diagnosing complaints.
The data is transmitted sequentially by means of the ECMU through terminal 21. The ECMU is supplied with DC battery voltage through terminals 1 and 2 and the switched ignition voltage through terminal 13. The ECMU is grounded through terminals 14 and 15.
Diagnostic process
Use the following procedure when servicing the ABS/DDRP system.
1. Check the mechanical properties of the vehicle's braking system.
2. Check the brake fluid level in the reservoir.
3. Check up purity of a liquid in the main brake cylinder.
4. Check for a leak in the brake master cylinder/modulator.
5. Check brake parts on all wheels.
6. Check for brake sticking (brake switch adjustment).
7. Check the smooth operation of the brake pedal (no tension or lead).
8. Check brake pad wear/damage.
9. Check wheel bearings for wear/damage.
10. Check wheel speed sensors/wiring.
11. Check exciter rings for damage.
12. Check tire tread depth/wear.
13. Road test the vehicle.
Perform a circuit diagnostic check and follow the troubleshooting chart.
Clear all ABS troubleshooting codes after all system faults have been resolved.