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The ECM System Diagnostics

The ECM provides a flash code in the dash mounted "Check Engine" lamp in the event of malfunction in or of some component of the electronic control system. When the ECM detects a problem the "Check Engine" light will come ON, or is activated. At that time a failure diagnostic code will be entered and stored in the ECM memory. The failure code can be retrieved by 1) using the Caterpillar Electronic Control Service tool, or 2) using the "Check Engine" light if the bus is equipped with cruise control.

Check Engine Light Operation

When the ignition switch is turned ON, the lamp will illuminate for 5 seconds, which is a check to insure the lamp is working. The ECM can be programmed to notify the driver of an active fault or condition by blinking the lamp every 5 seconds after start-up.

The "Check Engine" lamp is also used to warn, by flashing rapidly, that the "Idle Shutdown Timer" will shut the engine down in 90 seconds. The driver can override the timer by depressing the brake pedal, if necessary, by doing so while the light is flashing. This is only if idle shutdown timer has been programmed to be overridden.

Retrieval of a Failure Code

If the bus is equipped with Cruise Control the failure code can be determined by the procedure outlined below. If not so equipped, it will be necessary to use an Electronic Control Service tool that is available from your Caterpillar dealer or from certain other major tool suppliers. Use of the service tool will enable the mechanic to retrieve codes stored in the ECM memory system for periods longer than a day.

Using the Cruise Control to Determine a Failure Code

  • 1.

    Start the engine.

  • 2.

    Turn the Cruise Control switch to the OFF position.

  • 3.

    Move the SET/RESUME switch to either position and

hold that position until the "Check Engine" lamp begins to

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