Operation

OPERATION

The coolant low indicator gives an indication to the vehicle operator when the engine coolant level is low. This indicator is controlled by a transistor on the instrument cluster circuit board based upon cluster programming and electronic messages received by the cluster over the Controller Area Network (CAN) data bus from the Body Control Module (BCM) (also known as the Signal Acquisition and Actuation Module/SAM).

The coolant low indicator Light Emitting Diode (LED) or icon and textual message display are completely controlled by the instrument cluster logic circuit, and that logic will only allow this indicator to operate or icon and textual message to be displayed when the instrument cluster detects that the ignition switch is in the ON position. Therefore, the LED or the icon and textual message will always be OFF when the ignition switch is in any position except ON. The LED only illuminates or the icon and textual message are only displayed when it is activated by the instrument cluster logic. The instrument cluster will turn ON the coolant low indicator for the following reasons:

- Bulb Test - On vehicles not equipped with the optional steering wheel buttons, each time the ignition switch is turned to the ON position the coolant low indicator is illuminated by the cluster briefly as a bulb test.
- Coolant Level Low Indicator Lamp-On Message - On vehicles not equipped with the optional steering wheel buttons, each time the cluster receives an electronic coolant level low indicator lamp-ON message from the BCM, the coolant level low indicator will be illuminated. The indicator remains illuminated until the cluster receives a lamp-OFF message from the BCM, or until the ignition switch is turned to the OFF position, whichever occurs first. On vehicles equipped with the optional steering wheel buttons, each time the cluster receives an electronic coolant level low indicator lamp-ON message from the BCM, an icon and Coolant - Check level textual message will appear within the cluster multi-function display. The icon and textual message remain displayed until the message is acknowledged by momentarily depressing one of the steering wheel or cluster buttons, until the cluster receives a lamp-OFF message from the BCM, or until the ignition switch is turned to the OFF position, whichever occurs first.

The BCM continually monitors the engine coolant level switch integral to the coolant bottle to determine the current coolant level. The BCM then sends the proper lamp-ON or lamp-OFF messages to the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN or KOMBI). If the BCM sends a lamp-ON message after the bulb test, it indicates that the BCM has detected that the engine coolant level is low, which could result in engine overheating and damage. The BCM will store a Diagnostic Trouble Code (DTC) for any malfunction it detects.

For proper diagnosis of the engine coolant level switch, the BCM, the EMIC, the CAN data bus or the electronic communication related to coolant level low indicator operation, a diagnostic scan tool is required. Refer to the appropriate diagnostic information.