COOLANT LOW INDICATOR

DESCRIPTION

A coolant low indicator is standard equipment on all instrument clusters. However, on vehicles not equipped with an optional diesel engine this indicator is electronically disabled. The coolant low indication appears within the cluster Vacuum Fluorescent Display (VFD) unit. The coolant low indicator consists of a textual LoCooL message which appears in place of the odometer information in the VFD unit.

The VFD is soldered onto the cluster electronic circuit board, and is visible through a window with a smoked clear lens located on the lower edge of the tachometer gauge dial face of the cluster overlay. The dark lens over the VFD prevents it from being clearly visible when it is not illuminated. The coolant low indicator appears in the same blue-green color and at the same lighting level as the odometer/trip odometer information when it is illuminated by the instrument cluster electronic circuit board.

The coolant low indicator is serviced as a unit with the VFD in the instrument cluster.

OPERATION

The coolant low indicator gives an indication to the vehicle operator when the diesel engine coolant level is low. This indicator is controlled by the instrument cluster logic circuit based upon cluster programming and a hard wired input received by the cluster from the engine coolant level switch.

The coolant low indicator function of the Vacuum Fluorescent Display (VFD) unit 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 VFD coolant low indication will always be OFF when the ignition switch is in any position except ON or START. The instrument cluster will turn ON the coolant low indicator for the following reasons:

• Engine Coolant Level Switch Input - Each time the cluster detects a low resistance or ground on the low coolant fluid level sense circuit (engine coolant level switch closed = engine coolant level low) while the ignition switch is in the ON position, the cluster applies an algorithm to ensure that the input is correct and not the result of coolant sloshing in the coolant reservoir. The cluster tests the status of the circuit about seven milliseconds after ignition ON, and about once every second thereafter, then uses an internal counter to count up or down. When the counter accumulates 30 ground inputs on the circuit, the coolant low indicator will be illuminated. If the ignition switch is in the ON position and the vehicle is not moving when the coolant level switch input is received, the VFD will repeatedly and sequentially cycle the coolant low indication in two second intervals with the odometer/trip odometer information and any other active warnings including: door ajar, gate ajar and glass ajar. If the vehicle is moving, or once the cluster of a non-moving vehicle receives an electronic vehicle speed message from the Powertrain Control Module (PCM) indicating a speed greater than zero, the warning sequence will consist of three complete display cycles with an audible single chime tone accompanying each cycle, then revert to only the visual coolant low indication and odometer/trip odometer display cycling until the low coolant fluid level sense input to the cluster is not closed or low resistance (engine coolant level switch not closed or low resistance = engine coolant level full), or until the ignition switch is turned to the OFF position, whichever occurs first. The VFD can be reverted to the odometer display and any currently displayed textual messages suspended by momentarily depressing and releasing the odometer/trip odometer reset switch button on the front of the cluster.
• Engine Coolant Level Switch Input Fault - The engine coolant level switch also features a 3.3 kilohm diagnostic resistor connected in parallel between the switch input and output to provide the cluster with verification that the low coolant fluid level sense circuit is not open or shorted. If the cluster does not see a proper input on the low coolant fluid level sense circuit, it will suspend coolant low indicator operation. The indicator operation remains suspended until the low coolant fluid level sense circuit fault is resolved.

The engine coolant level switch on the coolant bottle provides a hard wired ground input to the ElectroMechanical Instrument Cluster (EMIC) circuitry through the low coolant fluid level sense circuit whenever the level of the coolant in the bottle is low. The switch and the hard wired circuits of the switch may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information.

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