Electronic Control System Signature, ISX and QSX15 Engines – 019-308   Ignition Relay Circuit

Turn the keyswitch to the OFF position.

Disconnect the OEM harness connector from the ECM.

Disconnect the idle shutdown/ignition bus relay harness connector from the OEM harness.

Set the multimeter to measure resistance.

CAUTION  To avoid pin and harness damage, use test lead, Part No. 3822758, when taking a measurement.

Touch one of the multimeter leads to pin 35 of the OEM harness connector.

Touch the other multimeter lead to the ignition bus relay harness connector pin.

Read the value displayed on the multimeter.

The multimeter

must display a reading of less than 10 ohms, which is a closed circuit.

If the circuit is

not closed, repair or replace the OEM harness. Refer to Procedure

019-250 or

019-071.

Connect all components after completing the repair.

Turn the keyswitch to the OFF position.

Disconnect the OEM harness connector from the ECM.

Disconnect the idle shutdown/ignition bus relay harness connector from the OEM harness.

Set the multimeter to measure resistance.

CAUTION  To avoid pin and harness damage, use test lead, Part No. 3822758, when taking a measurement.

Touch one of the multimeter leads to pin 35 of the OEM harness connector.

Touch the other multimeter lead to the engine block ground.

Read the value displayed on the multimeter.

The multimeter

must display a reading of more than 100k ohms, which is an open circuit.

If the circuit is

not open, repair or replace the OEM harness. Refer to Procedure

019-250
or

019-043.

Connect all components after completing the repair.

Turn the keyswitch to the OFF position.

Disconnect the OEM harness connector from the ECM.

Disconnect the idle shutdown/ignition bus relay harness connector from the OEM harness.

Set the multimeter to measure resistance.

CAUTION  To avoid pin and harness damage, use test lead, Part No. 3822758, when taking a measurement.

Touch one of the multimeter leads to pin 35 of the OEM harness connector.

Touch the other multimeter lead to all other pins in the connector.

Read the value displayed on the multimeter.

The multimeter

must display a reading of more than 100k ohms, which is an open circuit.

If the circuit is

not open, there is a short circuit between pin 35 and any other pin that registered a closed circuit. Repair or replace the OEM harness. Refer to Procedure

019-250 or

019-043.

Connect all components after completing the repair.

Disconnect the OEM harness connector from the ECM.

Disconnect the idle shutdown/ignition bus relay harness connector from the OEM harness.

Set the multimeter to measure VDC.

Turn the keyswitch to the ON position.

CAUTION  To avoid pin and harness damage, use test lead, Part No. 3822758, when taking a measurement.

Touch one of the multimeter leads to pin 35 of the OEM harness connector.

Touch the other multimeter lead to the engine block ground.

Read the value displayed on the multimeter.

The multimeter

must display a reading of less than 1.5 VDC.

If the voltage is

not less than 1.5 VDC, there is a short circuit to an external voltage source.

NOTE: An external voltage source is any wire in the OEM or engine harness wiring that carries voltage.

Remove the external voltage source.

Connect all components after completing the repair.