Contents: Valve relay ↧ Wheel speed sensors ↧ ABS warning light (yellow) ↧ Brake warning light (red) ↧ Diagnostics ↧ The diagnostic process ↧
EMUT - electronic brake control module.
EMUT performs the following functions:
- Checking the wheel speed sensor inputs.
- Determination of wheel locking tendency.
- Control of the brake system in the anti-lock braking system control mode.
- Checking the system for proper electrical operation.
The ECCM continuously monitors the speed of each wheel to determine whether the wheel is about to lock. If a tendency to lock is detected, the ECCM commands the appropriate valve to regulate the brake fluid pressure in some or all hydraulic circuits to prevent wheel lock and provide optimum braking. The ECCM continues to monitor the pressure in individual hydraulic circuits until there is no tendency to lock. The ECCM also continuously monitors the proper functioning of the ABS. If the ECCM detects an error, it can disable the ABS function and illuminate the ABS warning light in the instrument cluster. The ECCM also monitors the display of fault codes in the diagnostic mode.
Valve relay
The valve relay supplies power to the electric pump and solenoids. The switch in the relay is normally open, but during initialization it closes. The relay switch remains closed for the remainder of the drive cycle unless a fault code is present, which allows the switch to open. If a fault code is present that requires the relay to command off, battery voltage is removed from the electric pump and solenoids for the remainder of the current drive cycle and the ABS cannot function. The relay is an integral part of the ECU and cannot be serviced separately.
Wheel speed sensors
A wheel speed sensor is present on each wheel. The sensors transmit wheel speed information to the ECM using a small alternating voltage. This voltage is created by magnetic induction caused by the sensor toothed ring passing. The amplitude and frequency of the alternating voltage are proportional to the wheel speed and increase with increasing speed. The signal is transmitted to the ECM via an interface, which can result in an incorrect or noisy wheel speed sensor input signal. Two different types of wheel speed sensors are used for the DBC7 system.
ABS warning light (yellow)
The ABS warning light is located in the instrument cluster and illuminates when a fault in the ABS is detected by the ECMU. The ABS warning light informs the driver that a condition exists that has caused the anti-lock braking function to be disabled. If only the ABS warning light illuminates, normal full-power braking is present.
Below are the conditions under which the ABS warning light comes on.
ABS malfunction detected. As described above, the ABS warning light comes on when a malfunction 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 goes out.
Brake warning light (red)
The red brake warning light is located in the instrument cluster and illuminates to warn the driver that the brake system condition may result in reduced braking ability. The light illuminates 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 closing the brake fluid level switch (low level) the brake warning light remains on until the problem is corrected. Also, some fault modes in the DBC7 system will turn on the warning light to notify the driver that DDRP has been disabled.
Diagnostics
The Diagnostic Circuit Test is an organized approach to determining the problem created by an ABS/DDRP system malfunction. The technician should begin diagnosing any ABS/DDRP malfunction with a Diagnostic Circuit Test. The Diagnostic Circuit Test directs the service technician to the next logical step in diagnosing the complaint.
The data is transmitted sequentially using the EMCU via terminal 21. The EMCU is supplied with constant battery voltage via terminals 1 and 2 and switched ignition voltage via terminal 13. The EMCU is grounded via terminals 14 and 15.
The 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 the cleanliness of the fluid in the master brake cylinder.
4. Check for leaks in the master cylinder/modulator.
5. Check the brake components on all wheels.
6. Check for brake sticking (adjusting the brake switch).
7. Check for smooth pressing of the brake pedal (without tension or advance).
8. Check brake pads for wear/damage.
9. Check wheel bearings for wear/damage.
10. Check wheel speed sensors/wiring.
11. Check the exciter rings for damage.
12. Check tire tread depth/wear.
13. Road test the vehicle.
Perform a diagnostic circuit check and perform the troubleshooting steps in the troubleshooting table.
Clear all ABS diagnostic trouble codes after all system faults have been corrected.
(The article was reprinted from the website: ChevyMan)