nosis and testing time. Perform a visual inspection
for loose, disconnected, damaged, or misrouted wires
or connectors; include the following components and
areas of the vehicle in the inspection.
(1) Inspect fuses in the power distribution center
(PDC) and the wiring junction block. Verify that all
fuses are fully inserted into the PDC and wiring
junction block. A label on the underside of the PDC
cover identifies the locations of the ABS fuses.
(2) Inspect the 25-way electrical connector at the
CAB for damaged, spread, or backed-out wiring ter-
minals. Verify that the 25-way connector is fully
inserted in the socket of the CAB. Be sure that wires
are not stretched tight or pulled out of the connector.
(3) Verify that all the wheel speed sensor connec-
tions are secure.
(4) Look for poor mating of connector halves or ter-
minals not fully seated in the connector body.
(5) Check for improperly formed or damaged ter-
minals. All connector terminals in a suspect circuit
should be carefully reformed to increase contact ten-
sion.
(6) Look for poor terminal-to-wire connections.
This requires removing the terminal from the connec-
tor body to inspect it.
(7) Verify pin presence in the connector assembly
(8) Check for proper ground connections. Check all
ground connections for signs of corrosion, loose fas-
teners, or other potential defects. Refer to the wiring
diagrams for ground locations.
(9) Look for problems with the main power sources
of the vehicle. Inspect the battery, generator, ignition
circuits and other related relays and fuses.
If a visual check does not find the cause of the
problem, operate the car in an attempt to duplicate
the condition and record any trouble codes.
Most failures of the ABS disable the ABS function
for the entire ignition cycle even if the fault clears
before key-off. There are some failure conditions,
however, that allow ABS operation to resume during
the ignition cycle in which the trouble occurred even
if the trouble conditions are no longer present.
The following trouble conditions may result in
intermittent illumination of the amber ABS warning
lamp.
• Low system voltage. If Low System Voltage is
detected by the CAB, the CAB will turn on the
amber ABS warning lamp until normal system volt-
age is achieved. Once normal voltage is seen at the
CAB, normal operation resumes.
Additional possible causes that may result in the
illumination of the amber ABS warning lamp are as
follows:
• High system voltage. If high system voltage is
detected by the CAB, the CAB will turn on the
amber ABS warning lamp. If the ignition key is
cycled and normal voltage is again detected by the
CAB, normal ABS operation resumes and the lamp
remains off.
• Any condition that interrupts electrical current
to the CAB may cause the amber ABS warning lamp
to turn on intermittently.
• If PCI communication between the mechanical
instrument cluster (MIC) and the CAB is inter-
rupted, the MIC can turn on the amber ABS warning
lamp.
TONE WHEEL
Tone wheels can cause erratic wheel speed sensor
signals. Inspect tone wheels for the following possible
causes.
• missing, chipped, or broken teeth
• contact with the wheel speed sensor
• wheel speed sensor to tone wheel alignment
• wheel speed sensor to tone wheel clearance
• excessive tone wheel runout
• tone wheel loose on its mounting surface
If a front tone wheel is found to need replacement,
the drive shaft must be replaced. No attempt should
be made to replace just the tone wheel. Refer to the
DIFFERENTIAL AND DRIVELINE group in this
service manual for removal and installation.
If a rear tone wheel is found to need replacement,
the rear hub and bearing must be replaced. No
attempt should be made to replace just the tone
wheel. Refer to the SUSPENSION group in this ser-
vice manual for removal and installation.
If wheel speed sensor to tone wheel contact is evi-
dent, determine the cause and correct it before
replacing the wheel speed sensor or tone wheel.
Check the gap between the speed sensor head and
the tone wheel to ensure it is within specifications.
Refer to SPECIFICATIONS in this section of the ser-
vice manual for the minimum and maximum wheel
speed sensor to tone wheel clearance.
Excessive wheel speed sensor runout can cause
erratic wheel speed sensor signals. Refer to SPECI-
FICATIONS in this section of the service manual for
the maximum allowed tone wheel runout. If tone
wheel runout is excessive, determine if it is caused
by a defect in the driveshaft assembly or hub and
bearing. Replace as necessary.
Tone wheels are pressed onto their mounting sur-
faces and should not rotate independently from the
mounting surface. Replacement of the front drive-
shaft or rear hub and bearing is necessary.
BRAKE FLUID CONTAMINATION
Indications of fluid contamination are swollen or
deteriorated rubber parts.
Swollen rubber parts indicate the presence of
petroleum in the brake fluid.
LH BRAKES 5 - 67
DIAGNOSIS AND TESTING (Continued)
To Next Page
Loading...
Need help?
General
