Dodge RAM TRUCK 1500 1995 Service Manual page 274

7 - 4 COOLING SYSTEM DIAGNOSIS mm
DIAGNOSIS
INDEX
page page
DRB Scan Tool 5 Preliminary Checks 5
On-Board Diagnostics (OBD) 4
ON-BOARD DIAGNOSTICS (OBD)
FOR CERTAIN COOLING
SYSTEM
COMPONENTS
The powertrain control module (PCM) has been
programmed to monitor certain cooling system com­
ponents on gasoline powered engines only:
• If the engine has remained cool for too long a pe­
riod, such as with a stuck open thermostat, a Diag­
nostic Trouble Code (DTC) number 17 can be
observed at the malfunction indicator lamp. This
lamp is displayed on the instrument panel as the
CHECK ENGINE lamp (Fig. 5). DTC number 17 is
not used with diesel powered engines.
Fig. 5 Check Engine Lamp Location
If the problem is sensed in a monitored circuit of­
ten enough to indicate an actual problem, a DTC is
stored. The DTC will be stored in the PCM memory
for eventual display to the service technician. If the
problem is repaired or ceases to exist, the PCM can­
cels the DTC after 51 engine starts.
Certain criteria must be met for a DTC to be en­
tered into PCM memory. The criteria may be a spe­
cific range of engine rpm, engine temperature and/or
input voltage to the PCM.
A DTC indicates that the PCM has recognized an
abnormal signal in a circuit or the system. A DTC
may indicate the result of a failure, but never iden­
tify the failed component directly.
It is possible that a DTC for a monitored circuit
may not be entered into memory even though a mal­
function has occurred. Refer to On-Board Diagnostics
(OBD) in Group 14, Fuel Systems for additional in­
formation.
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 instru­
ment panel as the CHECK ENGINE lamp (Fig. 5).
They can also be displayed through the use of the
Diagnostic Readout Box (DRB) scan tool. The DRB
connects to the data link connector in the engine
compartment (Fig. 6). For operation of the DRB, refer
to the appropriate Powertrain Diagnostic Procedures
service manual.
POWERTRAIN CONTROL
MODULE (PCM) J9414-11
Fig. 6 PCM and Data Link Connector—Typical
EXAMPLES:
• If the lamp (Fig. 5) 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.