Durango 2WD V6-3.7L (2009)
Overdrive Indicator Lamp: Description and Operation
Tow/Haul Indicator - Operation
OPERATION
The tow/haul indicator gives an indication to the vehicle operator when the tow/haul function switch has been selected, revising the shift schedule of the
electronically controlled automatic transmission. This indicator is controlled by a transistor on the instrument cluster circuit board based upon cluster
programming and electronic messages received by the cluster from the Powertrain Control Module (PCM) over the Controller Area Network (CAN) data
bus.
The tow/haul indicator Light Emitting Diode (LED) is completely controlled by the instrument cluster logic circuit. This logic only allows the indicator
to operate when the instrument cluster receives a battery current input on the fused ignition switch output (run-start) circuit. Therefore, the LED is always
off when the ignition switch is in any position except ON or START. The LED only illuminates when it is provided a path to ground by the instrument
cluster transistor. The instrument cluster turns on the tow/haul indicator for the following reasons:
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Tow/Haul Indicator Lamp-On Message - Each time the cluster receives an electronic tow/haul indicator lamp-on message from the PCM
indicating that the tow/haul shift schedule has been selected, the indicator illuminates. The indicator remains illuminated until the cluster receives a
lamp-off message from the PCM, or until the ignition switch is turned to the OFF position, whichever occurs first.
-
self Test - Each time the cluster is put through the self test, the tow/haul indicator turns on, then off again during the bulb check portion of the test
to confirm the functionality of the LED and the cluster control circuitry.
The PCM continually monitors the tow/haul switch to determine the proper outputs to the automatic transmission. The PCM then sends the proper
lamp-on or lamp-off message to the instrument cluster, also known as the Cab Compartment Node (CCN). For further diagnosis of the tow/haul indicator
or the instrument cluster circuitry that controls the LED, See: Instrument Panel, Gauges and Warning Indicators/Instrument Cluster / Carrier/Testing and
Inspection.
Use a diagnostic scan tool for proper diagnosis of the transmission control system, the PCM, the CCN, the CAN data bus or the electronic
communication related to tow/haul indicator operation. Refer to the appropriate diagnostic information.