Dakota 4WD V8-4.7L (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 of the tow/haul 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, and that logic will only allow this
indicator to operate when the instrument cluster receives a battery current input on the fused ignition switch output (run-start) circuit. Therefore, the LED
will always be 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 will turn 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 will be illuminated. 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.
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Actuator Test - Each time the cluster is put through the actuator test, the tow/haul indicator will be turned 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 ElectroMechanical Instrument Cluster (EMIC) (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 Cluster / Carrier/Testing and
Inspection/Component Tests and General Diagnostics.
For proper diagnosis of the transmission control system, the PCM, the EMIC, the CAN data bus or the electronic communication related to tow/haul
indicator operation a diagnostic scan tool is required. Refer to the appropriate diagnostic information.
