Dodge RAM TRUCK 1500 1995 Service Manual page 355

8A - 22 BATTERY/STARTING/CHARGING SYSTEMS DIAGNOSTICS
U S I N G O N - B O A R D D I A G N O S T I C S Y S T E M
GENERAL INFORMATION
The Powertrain Control Module (PCM) monitors
critical input and output circuits of the charging sys­
tem, making sure they are operational. A Diagnostic
Trouble Code (DTC) is assigned to each input and
output circuit monitored by the OBD system. Some
circuits are checked continuously and some are
checked only under certain conditions.
If the OBD system senses that a monitored circuit
is bad, it will put a DTC into electronic memory. The
DTC will stay in electronic memory as long as the
circuit continues to be bad. The PCM is programmed
to clear the memory after 50 engine starts, if the
problem does not occur again.
DIAGNOSTIC TROUBLE CODES
Diagnostic Trouble Codes (DTC) are two-digit num­
bers flashed on the malfunction indicator (Check En­
gine) lamp that identify which circuit is bad. A DTC
description can also be read using the DRB scan tool.
Refer to Group 14 - Fuel Systems for more informa­
tion.
A DTC does not identify which component in a cir­
cuit is bad. Thus, a DTC should be treated as a
symptom, not as the cause for the problem. In some
cases, because of the design of the diagnostic test
procedure, a DTC can be the reason for another DTC
to be set. Therefore, it is important that the test pro­
cedures be followed in sequence, to understand what
caused a DTC to be set.
See Generator Diagnostic Trouble Code chart for
DTC's which apply to the charging system. Refer to
the Powertrain Diagnostic Procedures manual to di­
agnose an on-board diagnostic system trouble code.
RETRIEVING DIAGNOSTIC TROUBLE CODES
To start this function, cycle the ignition switch ON-
OFF-ON-OFF-ON within 5 seconds. This will cause
any DTC stored in the PCM memory to be displayed.
The malfunction indicator (Check Engine) lamp will
display a DTC by flashing on and off. There is a
short pause between flashes and a longer pause be­
tween digits. All DTC's displayed are two-digit num­
bers, with a four-second pause between codes.
An example of a DTC is as follows:
(1) Lamp on for 2 seconds, then turns off.
(2) Lamp flashes 4 times pauses and then flashes 1
time.
(3) Lamp pauses for 4 seconds, flashes 4 times,
pauses, then flashes 7 times.
The two DTC's are 41 and 47. Any number of
DTC's can be displayed, as long as they are in mem­
ory. The lamp will flash until all stored DTC's are
displayed (55 = end of test).
GENERATOR DIAGNOSTIC TROUBLE CODE
Diagnostic
Trouble
Code
DRB Scan Tool
Display
Description of Diagnostic Trouble Code
12*. .. Battery Disconnect
Direct battery input to PCM was disconnected within the last 50 key-on cycles.
41**.............
Generator Field Not An open or shorted condition detected in the generator field control circuit.
Switching Properly
An open or shorted condition detected in the generator field control circuit.
46** .. Charging System
Battery voltage sense input above target charging voltage during engine operation.
Voltage Too High
47** .. Charging System Battery voltage sense input below target charging during engine operation.
Voltage Too Low Also, no significant change detected in battery voltage during active test of
generator output.
55* N / A Completion of fault code display on Check Engine lamp.
* Check Engine lamp will not illuminate at all times if this Diagnostic Trouble Code was recorded. Cycle ignition key as
described in manual and observe code flashed by Check Engine lamp.'
* * Check Engine lamp will illuminate during engine operation if this Diagnostic Trouble Code was recorded.
J958A-7