Dodge RAM TRUCK 1500 1995 Service Manual page 1198

14 - 116 GENERAL DIAGNOSIS—DIESEL ENGINE
Fig. 37 Check Engine Lamp—Typical Location
They can also be displayed through the use of the
Diagnostic Readout Box (DRB scan tool). The DRB
scan tool connects to the data link connector in the
engine compartment (Fig. 38). For operation of the
Bit
DRB, refer to the appropriate Powertrain Diagnostic
Procedures service manual.
POWERTRAIN CONTROL
MODULE (PCM) J9414-11
Fig. 38 Data Link Connector Location—Typical
E1AMPLES;
• If the lamp (Fig. 37) flashes 1 time, pauses and
flashes 2 more times, a flashing Diagnostic Trouble
Code (DTC) number 12 is indicated. If this code is
observed, it is indicating that the battery has been
disconnected within the last 50 key-on cycles. It
could also indicate that battery voltage has been dis­
connected to the PCM. In either case, other DTC's
may have been erased.
• If the lamp flashes 4 times, pauses and flashes 1
more time, a diagnostic trouble code (DTC) number
41 is indicated.
® If the lamp flashes 4 times, pauses and flashes 6
more times, a diagnostic trouble code (DTC) number
46 is indicated.
After any stored DTC information has been ob­
served, the display will end with a flashing DTC
number 55. This will indicate the end of all stored in­
formation.
Refer to the Diagnostic Trouble Code (DTC) charts
for DTC identification.
If the problem is repaired or ceases to exist, the
powertrain control module (PCM) cancels the DTC
after 51 engine starts.
Diagnostic trouble codes indicate the results of a
failure, but never identify the failed component di­
rectly.
Typical circuits of the data link connector are
shown in (Fig. 39).
ERASING
TROUBLE
CODES
After the problem has been repaired, use the DRB
scan tool to erase a Diagnostic Trouble Code (DTC).
Refer to the appropriate Powertrain Diagnostic Pro­
cedures service manual for operation of the DRB
scan tool.
Fuel injector Malfunctions: The PCM cannot de­
termine if the fuel injector is clogged, or the wrong
injector is installed. The fuel injectors on the diesel
engine are not controlled by the PCM.
Vacuum Assist: Leaks or restrictions in the vac­
uum circuits of vacuum assisted engine control sys­
tem devices are not monitored by the PCM.
Powertrain Control Module (PCM) System
Ground: The PCM cannot determine a poor system
ground. However, a DTC may be generated as a re­
sult of this condition.
Powertrain Control Module (PCM) Connector
Engagement: The PCM cannot determine spread or
damaged connector pins. However, a DTC may be
generated as a result of this condition.
HIGH AND LOW LIMITS
The powertrain control module (PCM) compares in­
put signal voltages from each input device. It will es­
tablish high and low limits that are programmed into
it for that device. If the input voltage is not within
specifications and other diagnostic trouble code
(DTC) criteria are met, a DTC will be stored in mem­
ory. Other DTC criteria might include engine rpm
limits or input voltages from other sensors or
switches. The other inputs might have to be sensed
by the PCM when it senses a high or low input volt­
age from the control system device in question.
ACCESSING DIAGNOSTIC TROUBLE CQDES
A stored diagnostic trouble code (DTC) can be dis­
played by cycling the ignition key ON-OFF-ON-
OFF-ON within three seconds and observing the
malfunction indicator lamp. This lamp is displayed
on the instrument panel as the CHECK ENGINE
lamp (Fig. 37).