Dodge RAM TRUCK 1500 1995 Service Manual page 212

5 - 40 ALL-WHEEL ANTILOCK BRAKE SYSTEM (ABS)
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ABS DIAGNOSTIC CONNECTOR LOCATION
The ABS diagnostic connector is clipped to the un­
der side of the knee bolster (Fig. 8). The connector is
positioned just below the steering column.
The diagnostic connector is a six-way type, is either
light blue or black in color, and is the ABS access
point for the DRB scan tool. System circuits can be
tested once the scan tool is plugged into the connec­
tor.
J9405-164
Fig. 8 ABS Diagnostic Connector Location
ABS NORMAL AND FAULT CONDITIONS
Wheel/Tire Size And Input Signals
Antilock system operation depends on accurate sig­
nals from the wheel speed sensors. Ideally, the vehi­
cle wheels and tires should all be the same size and
type to ensure accurate signals and satisfactory oper­
ation.
Operating Sound Levels
The pump, motor, and antilock valve solenoids may
produce some sound as they cycle on and off. This is
a normal condition and should not be mistaken for
faulty operation. Under most conditions however,
pump and solenoid valve operating sounds should not
be audible.
Vehicle Response In Antilock Mode
During antilock braking, the front/rear solenoid
valves cycle rapidly in response to antilock electronic
control unit inputs.
The driver will experience a light pulsing sensation
in the brake pedal and in the vehicle. This occurs as
the solenoid valves modulate fluid pressure as
needed. This is a normal condition during antilock
mode braking.
Steering Response
A modest amount of steering input is required dur­
ing extremely high deceleration braking, or when
braking on differing traction surfaces. An example of
differing traction surfaces would be when the left
side wheels are on ice and the right side wheels are
on relatively dry pavement.
Brake Pedal Pulsing
A pulsing sensation may be felt through the brake
pedal during antilock mode braking. This is a nor­
mal occurrence and should not be mistaken for a sys­
tem fault.
Loss Of Sensor Input
Wheel speed sensor malfunctions will most likely
be due to loose connections, damaged sensor wires, or
incorrect sensor air gap. An additional fault would be
a result of sensor and tone wheel misalignment or
physical damage. A faulty sensor can be located with
the scan tool.
Driver Induced Faults
The driver can induce system faults by pumping or
riding the brake pedal, or leaving the parking brakes
partially applied. Either condition will cause the an­
tilock warning light to illuminate, despite the fact
that an actual malfunction has not occurred.
Another driver induced fault involves holding the
brake pedal in an applied position while starting the
engine. This practice causes the stoplamp switch to
be in a closed position when the engine is started.
With the switch closed, the ABS system self check
feature will not be completed. The result is illumina­
tion of both warning lights and the entry of a trouble
code in system memory.
A1S WARNING LIGHT DISPLAY
Light Illuminates At Startup
The amber antilock light illuminates at startup as
part of the system self check feature. The light illu­
minates for 2-3 seconds then goes off as part of the
normal self check routine.
Light Remains On After Startup
An ABS fault is indicated when the amber light re­
mains on after startup. Diagnosis with the DRB scan
tool will be necessary to determine the faulty circuit.
Light Illuminates During Brake Stop
A system fault such as loss of speed sensor signal
or solenoid failure, will cause the amber warning
light to illuminate. The most effective procedure here
is to check for obvious damage first. Then check elec­
tronic circuits with the scan tool.
ABS CONTROL MODULE DIAGNOSIS .
The electronic module controls all phases of an­
tilock system operation. The module also differenti­
ates between normal and antilock mode braking.