Dodge ram truck 3500 1996 Service Manual page 238

5 - 54 BRAKES
B R
DIAGNOSIS AND TESTING (Continued)
methods can be used to remove the battery supply
voltage from the CAB.
• Disconnect CAB 14-way connector
• Disconnect battery ground connector
• Remove CAB fuse from fuse box
ABS SERVICE PRECAUTIONS
The ABS uses an electronic control module, the
CAB. This module is designed to withstand normal
current draws associated with vehicle operation.
Care must be taken to avoid overloading • the CAB
circuits. I n testing for open or short circuits, do
not ground or apply voltage to any of the cir­
cuits unless instructed to do so for a diagnostic
procedure. These circuits should only be tested
using a high impedance multi-meter or the DRB
tester as described in this section. Power should
never be removed . or applied. to any control module
with the ignition in the ON position. Before removing
or connecting battery cables, fuses, or connectors,
always turn the ignition to the OFF position.
CAUTION: Use only factory wiring harnesses. Do
not cut or splice wiring to the brake circuits. The
addition of after-market electrical equipment (car
phone, radar detector, citizen band radio, trailer
lighting, trailer brakes, ect.) on a vehicle equipped
with antilock brakes may affect the function of the
antilock brake system.
RWAL DIAGNOSIS
An RWAL system malfunction will be indicated by
illumination of the ABS warning lamp. In most cases,
the brake warning lamp will also be illuminated at
the same time. I f either or both warning lamps illu­
minate, the following six step troubleshooting proce­
dure should be implemented.
• Verify the customer's concern
• Determine any related symptoms
• Diagnose the concern
9 Isolate the concern
• Repair the concern
• Verify the repair
The RWAL diagnosis begins by verifying the cus­
tomers concern. This test starts by verifying the ABS
warning lamp and brake warning lamp operation.
When this test is complete, you will be instructed to
perform either RWAL DIAGNOSTIC PROCEDURES
TEST 1 or RWAL DIAGNOSTIC PROCEDURES
TEST 2. The test usually will begin with a brief
explanation of the procedure or provide guidelines for
the test. Then, you will begin with step 1. Each test
has four columns; STEP, ACTION, YES, and NO. You
will be guided through each test by the ACTION. The
ACTION questions will all have bullets (•) in front of
them. Answer all questions either with a YES or NO
statement. The YES or NO columns will guide you to
the next appropriate test.
Start - RWAL Diagnosis - Verifying the
Customer's Concern
Start the engine and monitor the brake warning
lamp and ABS warning lamp. Both lamps will illumi­
nate for a few seconds when the ignition is turned
on. I f the brake warning lamp and or ABS warning
lamp remain illuminated or do not come on, continue
on to the RWAL DIAGNOSTIC TEST PROCEDURES
TEST 1 section of this group. I f the warning lamps
illuminate for a few seconds and then go out, proceed
with this test.
With the engine running and the vehicle in PARK
or NEUTRAL, check the service brake. The brake
pedal should remain firm under steady foot pressure
and not travel too far towards the floor.
The vehicle can be test driven i f is determined that
the. base brake system is functioning normally.. Refer
to the Base Brake Diagnose and Testing section in
this group of the Service Manual i f the previous
checks determine a malfunction with the base
brakes.
Test Driving RWAL Complaint Vehicle
Most RWAL complaints will require a test drive as
part of the diagnostic procedure. The purpose of the
test drive is to duplicate and verify the customers
concern.
WARNING: Reduced braking may be encountered if
the vehicle is test driven with either the brake warn­
ing lamp or the ABS warning lamp illuminated.
Extreme caution should be used.
Perform both normal and firm braking stops in the
25-40 mph range. At least one complete ABS stop
should be performed. Determine i f there are any
unusual brake operating conditions such as vehicle
lead during braking, brakes grabbing, brakes drag­
ging, noise, low brake pedal, etc. I f the brake warn­
ing lamp and or ABS warning lamps illuminate
during the test drive, proceed to the RWAL DIAG­
NOSTICS PROCEDURES TEST 1 section in this
group. I f the vehicle leads during braking, the brakes
grab, the brakes are dragging, there is brake related
noise, a low brake pedal, etc., refer to the base brake
diagnosis section in this section of the Service Man­
ual. I f the warning lamps remain extinguished and
the brakes respond normally, then proceed to the
RWAL DIAGNOSTIC PROCEDURES TEST 2 section
in this group.