Cummins ISX11.9 CM2250 – Service Manual 019-268   Switched Maximum Operating Speed Switch

General Information

TOC

The maximum engine speed switch is an original equipment manufacturer (OEM) installed switch that allows a driver to select a lower, programmable maximum engine speed.

Certain applications, such as one that uses a hydraulic system, can possibly need to be protected from an overspeed condition. The operator can toggle this switch and limit the maximum engine rpm to a lower value in which the hydraulic system can safely operate.

 
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Resistance Check

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If INSITE™ electronic service tool is available, monitor the switched maximum operating switch for proper operation. If
not, follow the troubleshooting procedures in this section.

Locate the maximum engine speed switch. Label the wires with the location on the switch or the wire number.

Remove the electrical connectors from the switch.

Set the multimeter to measure resistance. Touch the other multimeter probe to the other terminal of the switch.

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Place the switch in the OFF position and measure the resistance. The multimeter
must show an open circuit (100k ohms or more).

If the circuit is
not open, the switch is defective. Refer to the OEM troubleshooting and repair manual for replacement procedures.

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Place the switch in the ON and measure the resistance. The multimeter
must show a closed circuit (10 ohms or less). If the circuit is
not closed, the switch is defective. Refer to the OEM troubleshooting and repair manual for the replacement procedures.

If the resistance value is correct, the switch
must still be checked for a short circuit to ground.

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Check for Short Circuit to Ground

TOC

Touch one of the multimeter probes to one of the switch terminals. Touch the other probe to chassis ground. Move the switch to the normal position and measure the resistance. The multimeter
must show an open circuit (100k ohms or more).

If the circuit is
not open, the switch has failed. Refer to the OEM troubleshooting and repair manual for replacement procedures.

If the switch passes all of the previous checks, the circuit
must be checked for an open circuit, a short circuit to ground, a short circuit from pin-to-pin, and a short circuit to an external voltage source.

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Last Modified:  30-May-2008