On-Board Diagnostics (Obd); Water Pump Mounted Fan Drive; Powertrain Control Module (Pcm); Diagnosis And Testing - Jeep Wrangler 1997 Manual

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DESCRIPTION AND OPERATION (Continued)
THERMAL
VISCOUS
FAN DRIVE
(4) FAN BLADE-TO- (4) FAN HUB-TO-PUMP
VISCOUS DRIVE PULLEY STUDS
BOLTS
PUMP
FAN
PULLEY
(4) FAN HUB-TO-PUMP PULLEY NUTS BLADE
J9307-7
Fig. 9 Water Pump Mounted Fan Drive
MOUNTING
VISCOUS HUB
FAN DRIVE
THERMOSTATIC
SPRING
J9507-37
Fig. 10 Viscous Fan Drive-Typical
CAUTION : Engines equipped with serpentine drive
belts have reverse rotating fans and viscous fan
drives. They are marked with the word REVERSE to
designate their usage. Installation of the wrong fan
or viscous fan drive can result in engine overheat-
ing.
CAUTION: If the viscous fan drive is replaced
because of mechanical damage, the cooling fan
blades should also be inspected . Inspect for fatigue
cracks, loose blades, or loose rivets that could
have resulted from excessive vibration . Replace fan
blade assembly if any of these conditions are
found. Also inspect water pump!bearing and shaft
COOLING SYSTEM 7 - 7
assembly for any related damage due to a viscous
fan drive malfunction .
DIAGNOSIS AND TESTING
ON-BOARD DIAGNOSTICS (OBD)
FOR CERTAIN COOLING SYSTEM
COMPONENTS
The powertrain control module (PCM) has been
programmed to monitor the certain following cooling
system components:
" If the engine has remained cool for too long a
period, 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.
If the problem is sensed in a monitored circuit
often 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 (Fig.
11) . If the problem is repaired or ceases to exist, the
PCM cancels the DTC after 51 engine starts.
PCM
MOUNTING
BOLTS (3)
(3) 32-WAY
CONNECTOR\
POWERTRAIN
CONTROL MODULE
(PCM)
Fig.
11 Powertrain Control Module (PCM)
Certain criteria must be met for a DTC to be
entered into PCM memory. The criteria may be a
specific 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