Dodge RAM TRUCK 1500 1995 Service Manual page 1149

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GENERAL DIAGNOSIS—EXCEPT DIESEL 14 - 67
Fig, 46 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. 47). For operation of the
DRB, refer to the appropriate Powertrain Diagnostic
Procedures service manual.
EXAMPLES:
• If the lamp (Fig. 46) 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.
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 CODES
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. 46).
N O N - M O N I T O R E D CIRCUITS
The PCM does not monitor the following circuits,
systems or conditions that could have malfunctions
that result in driveability problems. A diagnostic
trouble code (DTC) may not be displayed for these
conditions.
Fuel Pressure; Fuel pressure is controlled by the
fuel pressure regulator. The PCM cannot detect a
clogged fuel pump inlet filter, clogged in-line fuel fil­
ter, or a pinched fuel supply or return line. However,
these could result in a rich or lean condition causing
an oxygen sensor DTC to be stored in the PCM.
Secondary Ignition Circuits The PCM cannot
detect an inoperative ignition coil, fouled or worn
spark plugs, ignition cross firing, or open circuited
spark plug cables.
Engine Timings The PCM cannot detect an incor­
rectly indexed timing chain, camshaft sprocket or
crankshaft sprocket. The PCM also cannot detect an
incorrectly indexed distributor. However, these could
result in a rich or lean condition causing an oxygen
sensor DTC to be stored in the PCM.
Cylinder Compressions The PCM cannot detect
uneven, low, or high engine cylinder compression.
Exhaust Systems The PCM cannot detect a
plugged, restricted or leaking exhaust system.
Fuel Injector Malfunctions: The PCM cannot de­
termine if the fuel injector is clogged, or the wrong
injector is installed. However, these could result in a
rich or lean condition causing an oxygen sensor DTC
to be stored in the PCM.
Excessive OH Consumption: Although the PCM
monitors exhaust stream oxygen content through ox­
ygen sensor (closed loop), it cannot determine exces­
sive oil consumption.
Throttle Body Air Flow: The PCM cannot detect
a clogged or restricted air cleaner inlet or air cleaner
element.
Evaporative System: The PCM will not detect a
restricted, plugged or loaded EVAP canister.
Vacuum Assist: Leaks or restrictions in the vac­
uum circuits of vacuum assisted engine control sys­
tem devices are not monitored by the PCM. However,
a vacuum leak at the MAP sensor will be monitored
and a diagnostic trouble code (DTC) will be gener­
ated 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.
H I O H AND LOW LIMITS
The powertrain control module (PCM) compares in­
put signal voltages from each input device. It will es-