Ignition Sequence

c2 dm 04.01.003

When the ignition is turned on, all the electronic gauges complete a full sweep of their dials, the warning and indicator lamps illuminate, and the buzzer sounds for 3 seconds.

Note: The air gauges do not sweep.
Important: If any emergency exit is not closed a buzzer will sound continuously.

The following lamps illuminate during the ignition sequence:

  • fasten seat belt warning

  • low battery voltage warning

  • high coolant temperature warning

  • low engine oil pressure warning

  • low air brake pressure warning

  • parking brake on indicator

  • all engine indicator/warning lamps, including check engine and stop engine

  • all ABS indicator/warning lamps, including wheel spin, and tractor ABS (if installed)

Note: While the engine and ABS warning lamps illuminate during the ignition sequence, they are not controlled by the instrument cluster but by their own system electronic control unit (ECU).

When the ignition switch is turned on, the ICU performs a self-test, looking for active faults. During the first half of the self-test, all segments of the display illuminate as follows:

  • First line (odometer): 888888.8

  • Second line (units): TRIP MI KM HOURS

  • Third line (voltmeter): 38.8 VOLTS

  • Fourth line: SERVICE ENGINE

During the second half of the self-test, the software revision level is displayed.

If there are no active faults, the driver display screen displays the odometer.

If however, the instrument cluster has received active fault codes from other devices, it displays them one after the other until the parking brake is released, or the ignition switch is turned off. Once the parking brake is released, the dash message center displays the odometer again.

Note: If active faults are present, take the vehicle as soon as possible to an authorized Thomas Built Bus service facility.

If the fault requires immediate attention, the stop engine system will activate. In most cases, the check engine lamp will also illuminate.

Some examples include:

  • high coolant temperature

  • low air pressure

  • low coolant level

  • low engine oil pressure

Note: The check engine lamp does not illuminate for a low air pressure fault.

The legend SERVICE ENGINE can appear on the driver display screen as an active fault code. If this legend appears, it means the trip miles (or hours) have gone beyond the next required service interval, as set by the vehicle operator.

Important: If the legend SERVICE ENGINE does appear on the driver display screen while operating the vehicle, bring the vehicle to an authorized Thomas Built Bus service facility when convenient.
Note:
Parent topic: Instrumentation Control Unit, ICU3S
Document Number: 0000106889
Manual Publication Date: 2025-12-10
Topic Publication Date: 2025-12-09