Grand Cherokee 2WD L6-4.0L VIN S (1997)
If the Powertrain Control Module (PCM) receives an incorrect signal, or no signal from certain sensors or emission related systems, the lamp is
turned on. This is a warning that the PCM has recorded a system or sensor malfunction. In some cases, when a problem is declared, the PCM will
go into a limp-in mode. This is an attempt to keep the system operating. It signals an immediate need for service.
The lamp can also be used to display a Diagnostic Trouble Code (DTC). Cycle the ignition switch On-Off-On-Off-On within three seconds and
any codes stored in the PCM memory will be displayed. This is done in a series of flashes representing digits.
The lamp is also used to indicate certain engine misfires.
Manual Transmission
MANUAL TRANSMISSION
If equipped with a manual transmission, this Powertrain Control Module (PCM) output will control operation of the shift indicator lamp (if
equipped with lamp). The lamp is controlled by the PCM. The lamp illuminates on the instrument panel to indicate when the driver should shift to
the next highest gear for best fuel economy. The PCM will turn the lamp OFF after 3 to 5 seconds if the shift of gears is not performed. The lamp
will remain off until vehicle stops accelerating and is brought back to range of up-shift lamp operation. This will also happen if vehicle is shifted
into fifth gear.
The indicator lamp is normally illuminated when the ignition switch is turned on and it is turned off when the engine is started up. With the engine
running, the lamp is turned ON/OFF depending upon engine speed and load.
Overdrive Lamp
OVERDRIVE LAMP-PCM OUTPUT
This circuit controls a signal for the operation of the instrument panel mounted push-button overdrive lamp switch. When the lamp is illuminated,
the overdrive is disengaged.
Power Ground
POWER GROUND
The power ground is used to control ground circuits for the following Powertrain Control Module (PCM) loads:
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Generator field winding
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Fuel injectors
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Ignition coil
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Certain relays/solenoids
Speed Control Solenoids
SPEED CONTROL SOLENOIDS-PCM OUTPUT
Speed control operation is regulated by the Powertrain Control Module (PCM). The PCM controls the vacuum to the throttle actuator through the
speed control vacuum and vent solenoids.
Tachometer
TACHOMETER-PCM OUTPUT
The Powertrain Control Module (PCM) supplies engine rpm values to the instrument cluster tachometer.
Three-Four Shift Solenoid
THREE-FOUR SHIFT SOLENOID-PCM OUTPUT
This output is used to control the transmission three-four shift solenoid. It is used on 4-speed electronically controlled automatic transmissions
only.
Torque Convertor Clutch (TCC) Solenoid
TORQUE CONVERTOR CLUTCH (TCC) SOLENOID- PCM OUTPUT
This circuit controls operation of the transmission mounted Torque Convertor Clutch (TCC) solenoid used for torque convertor engagement.
The Powertrain Control Module (PCM) will determine when to engage and disengage the solenoid by monitoring vehicle Miles Per Hour (mph)
versus the output voltage of the throttle position sensor. Also needed are various inputs from:
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Transmission temperature sensor
