Component Tests and General Diagnostics

Fig. 12 TECH 1 Scan Tool Operation (Part 1 Of 3):

Fig. 12 TECH 1 Scan Tool Operation (Part 2 Of 3):

Fig. 12 TECH 1 Scan Tool Operation (Part 3 Of 3):

Component testing can only be accomplished by using a TECH 1 scan tool or suitable equivalent. To access the different component tests, refer to the diagnostic process in Fig. 12.

AUTOMATED SELF-DIAGNOSING MODULATOR
If a mechanical modulator fault is suspected, rough ABS performance is indicated, or if any modulator service has been performed, this test should be run to verify the repair has corrected the problem and the displacement pistons are returned to their top most position. The scan tool will prompt for replies to changes in brake pedal position. These pedal changes are a result of modular component control in a specific order that allows component faults to be determined. It is important, when testing the rear channel, that each reply to the scan tool questions be carefully considered. During rear channel testing, pedal movement will be felt as as bump, which is much different than the movement felt in the front channels.

ABS AUTOMATED MOTOR PACK
This test should be performed to identify a potential problem in the motor pack assembly. If a problem exists, the results of the motor pack test will be indicated by the scan tool. If the motor is found to be defective, the motor pack is not serviceable and must be replaced as an assembly.

HYDRAULIC FUNCTIONAL CONTROL
This test is used to verify, ABS hold and ABS release functions. Raise and support the vehicle, then allow scan tool to perform the entire test.

MOTOR PACK FUNCTIONAL
The motor pack must be separated from the modulator to perform this test. Refer to ``Motor Assembly'' in ``Component Replacement.'' The scan tool will rotate the motors first in one direction, then the other. If any motor does not rotate in both directions, the motor pack is defective and must be replaced. If all three motors rotate, try to rotate each gear on the modulator assembly, refer to ``No Gear Movement Test.''

GEAR TENSION RELIEF SEQUENCE
When the displacement cylinder pistons are in their top most position, each motor has prevailing torque due to the force necessary to hold each piston 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 damaging the aluminum gears, this sequence will briefly reverse each motor to eliminate the prevailing torque.

ENABLE RELAY
This test monitors 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 relay is commanded ``OFF,'' the voltage should drop below five volts. Voltage will not drop to zero when relay contacts are open due to capacitors within the EBCM. If voltage drops below five volts, the relay is working properly.

VOLTAGE (BATTERY) LOAD
This ABS system can draw a significant amount of voltage when in operation. This test turns on many of the ABS system components to load test the vehicle electrical system. If low voltage faults or intermittent EBCM operation are occurring while this test is being performed. This test will allow monitoring of two separate power circuits for ABS (ignition and battery). If only one of these inputs drops below 10 volts during testing, a high resistance may be present in that power feed circuit.

ABS & RED BRAKE WARNING LAMP CONTROL
This test allows a functional test of the ABS warning light circuit, lamp driver module and brake warning light circuit.

ABS VERSION
This selection allows the display of the EEPROM identification, date code, sequence number and calibration identification.

MOTOR
In this test the motor can be turned on manually for up to five seconds at a current of 10 amps forward or 6 amps reverse. To verify correct front motor operation, the test must be done with engine off and all vacuum reverse depleted. Depress brake pedal as you would during a normal stop. ``Release'' one of the motors. Brake pedal should move smoothly towards the floor. Rough or jumpy brake pedal movement indicates an intermittent electrical connections within the motor. As the pedal drops, the feedback current should momentarily drop to only a few amps (indicating motor movement), and then become equal to the command current (6 amps), this indicates the motor is no longer moving since the displacement cylinder has bottomed out. With foot still on brake, ``Apply'' the same motor. Brake pedal should smoothly rise back up 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) as the displacement cylinder reaches the top of its travel and the motor stops moving. The rear motor is tested in the same manner, except there will only be a slight pedal drop and slight pedal rise.
If the brake pedal does not move in both directions and no trouble codes are set indicating an electrical problem, monitor the feedback current. If the feedback current is always only a few amps, the motor is free spinning. In either case, the motor pack must be separated from the hydraulic modulator to identify an ESB, motor, gear or ball screw problem.

SOLENOIDS
To functionally test the solenoids, select one front channel at a time. ``Release'' the motor for the channel and solenoid that is being tested. With foot off the brake pedal, turn ``ON'' the solenoid. Depress the brake, pedal should be very high and firm. If the pedal goes nearly to the floor, the solenoid is not closing or the check valve is leaking. Leaving brake pedal depressed, turn off the solenoid. The brake pedal should drop as the solenoid is being turned off. If the brake pedal does not drop and the motor is running, the solenoid is stuck on or off. To verify whether the solenoid is stuck on or off, depress the brake pedal and ``apply'' the motor for the channel that is being tested. If the brake pedal rises, the solenoid is stuck open or the check valve is leaking. If the pedal drops suddenly, the solenoid is stuck closed.
If when depressing the brake pedal, the pedal slowly sinks to the floor or the pedal rose during the ``apply,'' swap the two solenoids. Be sure to install the electrical connectors so that the left and right front channels are correct. Repeat the test for the other channel (different check valve but the same solenoid). If the solenoid does not check out (pedal also sank or rose during the second test), the solenoid is leaking and should be replaced. If the solenoid does check out, retest the first channel. If the brake pedal should rise or fall, indicating a leaking check valve, the ABS hydraulic modulator would have to be replaced.

NO GEAR MOVEMENT
If all three motors release, the motor pack appears to be satisfactory. Rotate each gear on the ABS hydraulic modulator assembly by hand. The front gears (non-center) should be able to rotate approximately 12 1/4 turns from lock to lock and the rear gear should turn approximately 7 1/4 turns. If the front gear will not freely turn at least 12 turns or the rear gear will not freely turn at least 7 turns, replace hydraulic modulator assembly.