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BRAKES
DIAGNOSIS AND TESTING (Continued)
START-UP CYCLE
The self diagnostic ABS start up cycle begins when
the ignition switch is turned to the on position. Elec-
trical checks are completed on ABS components, such
as the Controller, decay solenoid continuity, and the
system relay operation. During this check the Amber
ABS Warning Light is turned on for approximately 5
seconds.
DRIVE-OFF CYCLE
Further Functional testing is accomplished once
the vehicle is set in motion and reaches a speed of
about 7 mph. This cycle is performed only once after
each ignition on/off cycle.
• The solenoid valves and the pump/motor are
activated briefly to verify function. If the brake pedal
is applied at this time, the test is bypassed.
• The wheel speed sensor output is verified to be
within the correct operating range.
ONGOING TESTS
Other tests are performed on a continuous basis.
These include checks for decay solenoid continuity,
wheel speed sensor continuity and wheel speed sen-
sor output.
DIAGNOSTIC TROUBLE CODE INFORMATION
Fault codes are kept in the controller's memory
until either erased by the technician using the DRB
or erased automatically after the vehicle has been
driven 3500 miles. Fault codes are retained by the
controller even if the ignition is turned off or the bat-
tery is disconnected. The only fault that will not be
erased automatically is the (CAB) fault. A (CAB)
fault can only be erased by the technician using the
DRB diagnostic tester. More than one fault can be
stored at a time. The number of miles the vehicle has
been driven since the most recent fault was stored is
also displayed. Most functions of the (CAB) and ABS
system can be accessed by the technician for testing
and diagnostic purposes by using the DRB.
LATCHING VERSUS NON-LATCHING ABS
FAULTS
Some faults detected by the CAB are latching; the
fault is latched and ABS braking is disabled until the
ignition switch is reset. Thus ABS braking is non
operational even if the original fault has disap-
peared. Other faults are non-latching; any warning
lights that are turned on, are only turned on as long
as the fault condition exists. As soon as the condition
goes away, the ABS Warning Light is turned off,
although a fault code will be set in most cases.
INTERMITTENT DIAGNOSTIC TROUBLE CODES
As with virtually any electronic system, intermit-
tent faults in the ABS system may be difficult to
accurately diagnose.
Most intermittent faults are caused by faulty elec-
trical connections or wiring. When an intermittent
fault is encountered, check suspect circuits for:
(1) Poor mating of connector halves or terminals
not fully seated in the connector body.
(2) Improperly formed or damaged terminals. All
connector terminals in a suspect circuit should be
carefully reformed to increase contact tension.
(3) Poor terminal to wire connection. This requires
removing the terminal from the connector body to
inspect.
(4) Pin presence in the connector assembly
(5) Proper ground connections. Check all ground
connections for signs of corrosion, tight fasteners, or
other potential defects. Refer to wiring diagram man-
ual for ground locations.
(6) If a visual check does not find the cause of the
problem, operate the car in an attempt to duplicate
the condition and record the Fault code.
(7) Most failures of the ABS system will disable
ABS function for the entire ignition cycle even if the
fault clears before key-off. There are some failure
conditions, however, which will allow ABS operation
to resume during the ignition cycle in which a failure
occurred if the failure conditions are no longer
present. The following conditions may result in inter-
mittent illumination of the ABS Warning Lamp. All
other failures will cause the lamp to remain on until
the ignition switch is turned off. Circuits involving
these inputs to the (CAB) should be investigated if a
complaint of intermittent warning system operation
is encountered.
(8) Low system voltage. If Low System Voltage is
detected by the CAB, the CAB will turn on the ABS
Warning Lamp until normal system voltage is
achieved. Once normal voltage is seen at the CAB,
normal operation resumes.
(9) Additionally, any condition which results in
interruption of electrical current to the CAB or mod-
ulator assembly may cause the ABS Warning Lamp
to turn on intermittently.
TONEWHEEL INSPECTION
Carefully inspect tonewheel at the suspected faulty
wheel speed sensor for missing, chipped or broken
teeth, this can cause erratic speed sensor signals.
Tonewheels should show no evidence of contact
with the wheel speed sensors. If contact was made,
determine cause and correct before replacing the
wheel speed sensor.
Excessive runout of the tonewheel can cause
erratic wheel speed sensor signals. Refer to Tone-
JA
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