CM2150 Electronic Control System – 019-028   Diagnostic Test Mode 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 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 the test lead into the diagnostic test mode switch signal pin in the OEM harness connector and connect it to the multimeter probe.

Touch the other probe to the engine block ground.

Move the ON/OFF switch to the ON position.

If the OEM wired the switch return to chassis ground, the multimeter
must show a closed circuit (10 ohms or less). If the circuit is
not closed, inspect the diagnostic test mode switch signal wire for an open circuit.

If the OEM wired the switch return to the OEM wire harness, the multimeter
must show an open circuit (100k ohms or more). If the circuit is
not open, inspect the diagnostic test mode switch signal wire for a closed circuit.

Refer to the OEM troubleshooting and repair manual.

If the resistance is within specification, the diagnostic test mode switch signal wire
must be checked for a short circuit to ground, a short circuit from terminal to terminal, and a short circuit to an external voltage source.

To isolate the diagnostic test mode switch signal circuit when checking for an electrical short, turn all cab panel switches to the OFF or neutral position.

Set the service brake using the trailer brake hand valve.

Disconnect the clutch pedal position switch.

Disconnect the idle validation switch.

Disconnect the OEM harness connector from the ECM. Set the diagnostic test mode switch to the OFF position.

Insert one of the test leads into the diagnostic test mode switch signal pin of the OEM harness connector and connect it to a multimeter probe.

Touch the other probe to engine block ground.

The multimeter
must show an open circuit (100k ohms or more).

Check for a short circuit from pin-to-pin. Isolate the switch circuit by setting the cab panel switches as described in the previous section. Set the diagnostic test mode switch to the OFF position. Insert a test lead into the switch return pin of the OEM harness connector and connect it to the multimeter probe. With the other lead inserted into the diagnostic test mode switch signal pin of the connector, measure the resistance. The multimeter
must show an open circuit (100k ohms or more).

Remove the lead from the switch return and test all pins in the connector. 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 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 vehicle keyswitch to the ON position. Set the diagnostic test mode switch to ON. Adjust the multimeter to measure VDC. Insert a test lead into the diagnostic test mode switch signal pin of the OEM harness connector. Touch the other lead 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 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.