CM850 Electronic Control System – 019-336   Engine Torque Limit Control Switch Circuit

Resistance Check

TOC

 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 torque limit switch circuit for proper operation. If
not, follow the troubleshooting procedures in this section.

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

NOTE: The torque limit switch is programmable by the OEM. The open or closed position of the switch can represent “Normal” or “Torque Limit” depending on how the OEM programs the switch. Before continuing to troubleshoot refer to the OEM troubleshooting and repair manual to determine how the switch is programmed and apply the defective switch criteria accordingly when performing the troubleshooting.

Move the torque limit switch to the normal position. The multimeter
must show a closed circuit (10 ohms or less). If the circuit is
not closed, inspect the switch return wire and the engine torque limit signal 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 switch return wire and the engine torque limit signal 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.

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Check for Short Circuit to Ground

TOC

To isolate the engine torque limit switch circuit when checking for an electrical short, disconnect the OEM harness from the ECM and the OEM harness from the engine torque limit switch. Disconnect the clutch pedal position switch/engine protection override switch and the accelerator pedal assembly. Set all cab panel switches to the OFF or neutral position. Set the service brake using the trailer brake hand valve.

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Adjust the multimeter to measure resistance. Insert a test lead into the engine torque limit 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 torque limit switch circuit, provided that the switch has been previously checked.

Repair or replace the wire connected to the engine torque limit control switch signal wire in the OEM harness. Refer to the OEM troubleshooting and repair manual.

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Check for Short Circuit from Pin to Pin

TOC

Isolate the engine torque limit switch circuit by setting the switches as in the previous section. Set the engine torque limit switch to the normal position. Insert the lead into the engine torque limit switch signal pin. Connect the alligator clip to the multimeter. With the other lead inserted into the switch return pin, measure the resistance. The multimeter
must show an open circuit (100K ohms or more).

Remove the lead from the engine torque limit 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 torque limit 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.

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Check for Short Circuit to External Voltage Source

TOC

Turn the keyswitch to the ON position. Set the engine torque limit switch to the normal position. Adjust the multimeter to measure VDC. Insert a test lead into the engine torque limit switch signal 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 torque limit switch circuit and a wire carrying power in the OEM harness. Remove the voltage source or repair the wiring in the OEM harness according to the vehicle manufacturer’s procedures.

Connect all components after completing the repair.

NOTE: If the engine torque limit switch circuit was approved in all of the previous tests, it is functioning correctly.

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Last Modified:  30-May-2008