ABS Hydraulic Diagnosis

AUTOMATED SELF-DIAGNOSING MODULATOR TEST
If a mechanical modulator malfunction is suspected, rough ABS performance 15 reported, or if any modulator service has been performed, it is strongly recommended this test be run to verify the repair has corrected the identified problem and the displacement cylinder pistons are returned to their top-most position. The Tech 1 will prompt you for replies to changes in the brake pedal position. These brake pedal changes are a result of modulator component control in a specific order that allows component malfunctions to be determined. It is very important, especially when testing the rear channel, that each reply to the Tech 1 questions be carefully considered. During rear channel testing, pedal movement will be felt as a bump, which is much different than the movement felt in the front channels.

AUTOMATED MOTOR PACK DIAGNOSIS TEST
Using the Tech I, the motor pack diagnosis test should be performed to identify a potential problem in the motor pack. If a problem exists, the results of the motor pack test will be indicated on the Tech 1.
If the motor is indicated to be malfunctioning the motor pack is not serviceable and must be replaced as an assembly.

NO GEAR MOVEMENT
If all three motors release at this point, the motor pack appears to function properly. Rotate each gear by hand on the hydraulic modulator. The front gears (non-center gears) should be able to be rotated approximately 8.75 full turns lock to lock. If the gear does not turn freely or at least 8.5 turns are not possible, replace the hydraulic modulator.

The rear gear should rotate approximately 3.75 turns. If the gear does not turn freely or at least 3.5 turns are not possible, replace the hydraulic modulator.

HYDRAULIC FUNCTIONAL CONTROL
This test is used to verify base brake apply and ABS release, hold, and apply functions. During testing, if a problem is encountered, the Tech 1 will provide information on the problem.
1. Ignition "OFF."
2. Raise the vehicle such that all wheels to be tested are off the ground.
3. Install Tech 1 with Brake Cartridge.
4. Ignition "ON."
5. Select a channel to test; left front, right front, or rear. When testing the rear brakes, both rear wheels should rotate and not rotate together at the various points in the test; this is true because both rear brake pressures are controlled together.
6. Firmly depress brake pedal. Pedal should remain high and firm.
7. Have an assistant attempt to rotate the wheel being tested. If the wheel does not rotate, base brake apply is working properly.
8. With the brake pedal still depressed, press the Up Arrow key on the Tech 1 to start the test. The brake pedal should remain high and firm. (If the brake pedal drops toward the floor, verify the solenoid electrical connectors are connected to the correct solenoids.
9. With the brake pedal still depressed, have the assistant attempt to rotate the wheel. The wheel should rotate with little or no resistance for the full 18 seconds of this test.
10. After 18 seconds, brake pressure will be applied, and a slight bump may be felt in the pedal. This is normal. The assistant should not be able to rotate the wheel at this point.

ELECTROMAGNETIC BRAKE FUNCTIONAL TEST
The Electromagnetic Brake (EMB) holds the motor when brake pressure is present. This test, with the brake depressed, attempts to release and then apply the motor with the EMB "OFF," or holding. If the brake pedal rises or falls when this test is performed, the EMB is not able to properly hold the motor, the motor pack must be replaced.

Important Electromagnetic Brake (EMB) "Chirping." An electrical diagnostic routine in this test verify briefly injects current into the EMBs once every second. Because the EMBs are electromagnetic devices, when the current injection stops, the magnetic field created rapidly collapses. This can be heard on some vehicles if the engine is not running and the hood is raised, the sound is normal.

MOTOR TESTING
Each motor can be manually turned "ON" for up to 5 seconds, at a current of 10 amps forward or 6 amps reverse.

The test below describes how front motors will operate, the rear motor can be tested in a similar manner, except there will he only a slight pedal drop (hump) and rise during the test.
1. Ignition "OFF."
2. Install Tech 1 with Brake Cartridge.
3. Ignition "ON," engine "OFF."
4. Pump brake pedal and deplete power booster.
5. Depress and hold brake pedal.
6. Using the Tech 1, "Release" one of the motors. The brake pedal should move smoothly toward the floor. As the pedal drops, the feedback current should momentarily drop to only a few amps (indicating motor movement) and then become equal to command current (6 amps). This indicates the motor is no longer moving since the piston has bottomed out.
^ Rough or "jumpy" pedal movement indicates an intermittent electrical connection within the motor or EMR.
7. With the brake pedal still depressed and at the floor, "Apply" the same motor. The brake pedal should now smoothly rise hack to the top of its travel. The feedback current should momentarily drop to a few amps, then quickly increase to the command current (10 amps). This indicates the motor is no longer moving since the piston has reached the top of its travel.

If the brake pedal does not move both up and down as indicated and there are no DTCs set, monitor the feedback current closely while performing the test again. If the feedback current is only a few amps, the motor is free-spinning. The motor pack must be separated from the hydraulic modulator to identify an EMB, ESB, motor, gear, or ball screw problem.

MOTOR PACK FUNCTIONAL TEST
Once the motor pack has been separated from the hydraulic modulator, this test will help determine if the motor pack is operating properly.

The Tech 1 will rotate the motors in one direction, then the other.
^ If any motor does not turn in both directions, the motor pack is malfunctioning and must he replaced.
^ If all three motors rotate, try to rotate each gear on the hydraulic modulator. Refer to "No Gear Movement".

ELECTROMAGNETIC BRAKE (EMB) TEST
1. Ignition "OFF."
2. Install Tech 1 with Brake Cartridge.
3. Ignition "ON," engine OFF."
4. Select manual control.
5. Select left front or right front.
6. Turn "ON" ("Release") the EMB.
7. Slowly depress the brake pedal and gradually increase the force. The brake pedal should begin to move toward the floor, indicating the motor has been released and is free to turn.

If the pedal does not drop, perform the following.
1. "Apply" the motor to be sure the piston is at the top of its travel.
2. Turn "ON" ("Release") the EMB.
^ If the pedal still does not drop, the EMB or motor is restricted or "bound up."
^ If the pedal drops toward the floor but is jerky, an EMB electrical connection may be intermittent. There should be a DTC set as well.
^ If no DTCs are set during testing or driving, separation of the motor pack from the hydraulic modulator is necessary for further diagnosis.

SOLENOID TEST
1. Ignition "OFF."
2. Install Tech 1 with Brake Cartridge.
3. Ignition "ON," engine "OFF."
4. Select left front or right front.
5. "Release" the motor for the channel being tested.
6. Select the solenoid for the same channel as that being tested.
7. With no brake pedal pressure applied, turn the solenoid "ON."
8. Depress the brake pedal. It should be very high and firm.
^ If the pedal goes nearly to the floor, the solenoid is leaking or not closing and/or the checkball is leaking.

9. With brake pressure still applied, turn the solenoid "OFF." The brake pedal should drop immediately.
^ If the pedal does not drop and the motor is moving, the solenoid is stuck "ON" or "OFF." Toverifyv which:

9a. With brake pressure still applied, "Apply" the motor for the channel being tested.
^ If the brake pedal rises, the solenoid is stuck "OFF" (open) or the check hall is leaking.
^ If the pedal drops suddenly, the solenoid is stuck "ON" (closed).

If, when depressing the pedal it slowly sinks toward the floor, or if it rises during the "Apply" of the motor, perform the following:
1. Physically switch the two solenoids.
2. Repeat the test for the channel in question.
^ If the pedal continues to sink, the check valve is leaking. Replace hydraulic modulator.
^ If the test now works properly, test the other channel. If the pedal sinks or rises, replace the solenoid in this channel.

ENABLE RELAY TEST
This test allows monitoring the voltage at the EBCM while turning the enable relay "ON" and "OFF."
When the relay is commanded "ON," the voltage should be equal to battery voltage. When the relay is "OFF ," the voltage should drop below 5 volts.

NOTICE: Voltage will not drop to zero when the relay contacts are open due to capacitors in the EBCM. If voltage drops below 5 volts, the relay is operating properly.

VOLTAGE LOAD TEST
The ABS VI system can draw significant amounts of current when operating. This test turns "ON" many of the system components to load-test the vehicle's electrical system.

If low voltage malfunctions or intermittent EBCM operation are occurring, this test will allow you to monitor two separate power circuits for ABS: ignition and battery. If only one of these two inputs drops below 1O volts during testing, a high resistance may be present in that power feed circuit.

GEAR TENSION RELIEF SEQUENCE
When the displacement cylinder pistons are in their topmost position, each motor has prevailing torque due to the force necessary to ensure each piston is held firmly at the top of its travel. This torque results in "gear tension," or force on each gear that makes motor pack separation difficult. To avoid injury, or damage to the gears, the "Gear Tension Relief Sequence" briefly reverses each motor to eliminate the prevailing torque.

Always perform the "Gear Tension Relief Sequence" prior to removing the hydraulic modulator/master cylinder assembly from the vehicle. Each hydraulic modulator gear (large gears) should be able to be turned in one direction and then in the opposite direction when the motor pack is removed. If any gear will not move, replace the hydraulic modulator.

ABS AND "BRAKE" LAMP CONTROL
This test allows a functional test of the ABS indicator lamp circuit and lamp driver module by flashing the lamp or turning it "ON" solid. The "BRAKE" warning lamp can be cycled "UN" and "OFF" using this test.