Chrysler RAM TRUCK 2500 1994 Service Manual page 198

• ALL-WHEEL ANTILOCK BRAKE SYSTEM (ABS) 5 - 39
ABS SYSTEM DIAGNOSIS
ABS system diagnosis involves checking only those
components that form the antilock system. Antilock
system diagnosis involves three basic steps which
are:
• observation of the warning light display
• visual examination for low fluid, leaks, or damaged
wires
• identification of the problem component
Visual examination includes a check of reservoir
fluid level and condition of the system components.
This includes inspection of the sensor wires and elec­
trical connections. Things to look for are leaks, loose
connections, or obvious component damage.
Identification of the problem component involves
using the DRB scan tool to identify a faulty compo­
nent.
ABS DIAGNOSTIC CONNECTOR LOCATION
The ABS diagnostic connector is clipped to the un­
der side of the knee bolster (Fig. 9). The connector is
positioned just below the steering column.
The diagnostic connector is a six-way type and is
either light blue or black i n color.
The connector is the ABS access point for the DRB
scan tool. System components can be tested after the
scan tool is attached to the connector.
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
On the all wheel ABS system, the pump/motor and
antilock valve solenoids may produce some sound as
they cycle on and off. This is a n o r m a l condition and
should not be mistaken for faulty operation. Under
most conditions, 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 i n response to antilock electronic
control unit inputs.
The driver may experience a slight pulsing sensa­
tion i n the brake pedal and vehicle as the solenoid
valves modulate fluid pressure as needed. This is a
normal condition.
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 light pulsing sensation may be felt through the
brake pedal during antilock mode braking. This is a
normal occurrence and should not be mistaken for a
system 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 (open, shorted) can
be located with the DRB scan tool.
Driver Induced Faults
The driver can induce system faults by riding the
brake pedal or leaving the parking brakes partially
applied. Either condition will cause the antilock
warning light to illuminate, despite the fact that an
actual malfunction has not occurred.
Another driver induced fault involves holding the
brake pedal i n an applied position while starting the
engine. This practice causes the stoplamp switch to
be i n 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 a trouble code to be
registered i n system memory.
ABS 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.