CM2150 Electronic Control System – 019-328   Engine Protection Override Switch Circuit

CAUTION  The leads must fit tightly in the connector without expanding the pins in the connector otherwise the connector will be damaged.

If INSITE™ electronic service tool is available, monitor the engine protection override switch circuit for proper operation. If
not, follow the troubleshooting procedures in this section.

Disconnect the original equipment manufacturer (OEM) harness connector from the electronic control module (ECM). Insert one of the test leads into the switch return negative (-) pin of the OEM harness connector and connect the alligator clip to the multimeter probe. Insert the other lead into the engine protection override switch signal pin of the OEM harness connector and connect the alligator clip to the other multimeter probe.

Move the engine protection override switch to the override (pressed) position. The multimeter
must show a closed circuit (10 ohms or less). If the circuit is
not closed, inspect the switch return negative (-) wire and the engine protection override switch wire for an open circuit, provided that the switch has been previously checked. Refer to the OEM troubleshooting and repair manual for repair procedures.

If the resistance is within the specification, the cab switch return negative (-) wire and the engine protection override switch wire
must be checked for a short circuit to ground, a short circuit from pin-to-pin, and a short circuit to an external voltage source.

To isolate the engine protection override switch circuit when checking for an electrical short, disconnect the OEM harness from the ECM connector and the OEM harness from the engine protection override switch. Disconnect the idle validation switch. Set all cab panel switches to the OFF or neutral position. Set the service brake using the trailer brake hand valve.

Adjust the multimeter to measure resistance. Insert a test lead into the engine protection override switch pin of the OEM harness connector and connect it to a multimeter probe. Touch the other multimeter probe to the engine block ground. Measure the resistance.

The multimeter
must show an open circuit (100k ohms or more). If the circuit is
not open, there is a short circuit to ground in the engine protection override switch circuit, provided that the switch has been previously checked.

Repair or replace the wire connected to cruise control input wire in the OEM harness according to the vehicle manufacturer’s procedure.

Check for a short circuit from pin-to-pin. Isolate the engine protection override circuit by setting the switches as in the previous section. Set the engine protection override switch to the override position. Insert the lead into the engine protection override switch pin. Connect the alligator clip to the multimeter. With the other lead inserted into the cab switch return negative (-) pin, measure the resistance. The multimeter
must show an open circuit (100k ohms or more).

Remove the lead from the engine protection override switch pin and check all other pins. Measure the resistance. The multimeter
must show an open circuit (100k ohms or more). If the circuit is
not open, there is a short circuit between the engine protection override switch circuit and any pin that shows a closed circuit, provided the switch has previously been checked.

Repair or replace the wires in the OEM harness. Refer to Procedure
019-071.

Turn the keyswitch to the ON position. Set the engine protection override switch to the override position. Adjust the multimeter to measure VDC. Insert a test lead into the engine protection override switch pin and attach it to a multimeter probe. Touch the other multimeter probe to the engine block ground. Measure the voltage. The voltage
must be 1.5 VDC or less.

If the voltage is
not correct, there is an external voltage source connected to the circuit, or there is a short circuit between the engine protection override switch circuit and a wire carrying power in the OEM harness. Remove the voltage source or repair the wiring in the OEM harness. Refer to Procedure
019-071. Connect all components after completing the repair.

NOTE: If the engine protection override switch circuit was approved in all of the previous tests, it is functioning properly.