Chrysler RAM TRUCK 2500 1994 Service Manual page 187

5 - 28 REAR WHEEL ANTILOCK BRAKE (RWAL) SYSTEM
•
contact with the drums. The valve is designed to
maintain front brake fluid pressure at
2 1 - 2 0 7
kPa
(3-30 psi) until the hold-off limit of approximately
807 kPa (117 psi) is reached. A t this point, the me­
tering valve opens completely permitting full fluid
apply pressure to the front disc brake calipers.
REAR WHEEL ANTILOCK SYSTEM DIAGNOSIS
An antilock system malfunction will be indicated
by illumination of the amber warning lamp.
I f a problem occurs, system diagnosis should begin
with a fluid level check followed by a visual exami­
nation of the system electrical and hydraulic connec­
tions. I f obvious defects (low fluid, leaks, loose
connections, etc.) are not evident, road test the vehi­
cle. A road test should help determine i f a malfunc­
tion is actually related to an antilock component.
During the road test, note i f other conditions are
evident such as a low pedal, pull, grab, or similar
condition. Remember that brake malfunctions such
as low fluid, system leaks, or parking brakes par­
tially applied will affect antilock system operation.
The idea is to determine i f a malfunction is actually
related to an antilock component.
If a visual inspection and road test do not indicate the
problem cause, check the system fault codes. Refer to
the system fault code information in this section.
DIAGNOSTIC FAULT FLASH CODES
The microprocessor i n the electronic control module
has a self test feature. This feature is activated
whenever the ignition switch is i n the On and Run
positions.
I f a system fault is detected, the control module i l ­
luminates the antilock light and stores the fault code
in the microprocessor memory. I f a fault code is gen­
erated, the module will retain the code after turning
the ignition switch to Off position.
System faults are identified by a series of flash
codes that operate through the antilock warning
light. Temporarily grounding the antilock diagnostic
connector will produce the flash code sequence. Refer
to Fault Code Identification i n this section.
FAULT CODE CAPACITY
The microprocessor memory will store and display
only one fault code at a time. The stored code can be
displayed by grounding the antilock diagnostic connec­
tor.
FAULT CODE IDENTIFICATION
When a fault code is generated, the red brake
warning lamp will also illuminate. To determine
what the fault code is, momentarily ground the diag­
nostic connector and count the number of times the
antilock indicator lamp flashes. Fault codes and typ­
ical malfunctions are outlined i n Figure 6.
The initial flash will be a long flash followed by a
number of short flashes. The long flash indicates the
beginning of the fault number sequence and the
short flashes are a continuation of that sequence.
You must count the long flash along with the
short flashes for an accurate fault code count.
CLEARING A FAULT CODE
To clear a fault code, disconnect the control module
connector or disconnect the battery for a minimum of
five seconds. During system retest, wait 30 seconds
to be sure the fault code does not reappear.
F A U L T
CODE
NUMBER
TYPICAL FAILURE DETECTED
1
Not used.
2
Open isolation valve wiring or bad control
module.
3 Open dump valve wiring or bad control
module.
4 Closed RWAL valve switch.
5
Over 16 dump pulses generated in 2WD
vehicles (disabled for 4WD).
6
Erratic speed sensor reading while rolling.
7
Electronic control module fuse pellet open,
isolation output missing, or valve wiring
shorted to ground.
8
Dump output missing or valve wiring shorted to
ground.
9
Speed sensor wiring/resistance (usually high
reading).
10
Sensor wiring/resistance (usually low reading).
11
Brake switch always on. RWAL light comes on
when speed exceeds 40 mph.
12 Not used.
13 Electronic control module phase lock loop
failure.
14
Electronic control module program check
failure.
15 Electronic control module RAM failure.
J9005-101
Fig. 6 RWAL Antilock System Flash Codes