Electronic Control System ISM and QSM11 Engines – 019-027   Diagnostic Test Mode Switch

CAUTION  The diagnostic switch must remain in the OFF position (shorting plug removed) while the engine is being operated in order for all fault codes to be logged.

The diagnostic on/off switch circuit signals the system that the operator is requesting to read any active fault code recorded in the ECM.

NOTE: Some OEMs use a shorting plug rather than a switch.

When the ECM receives the signal from the diagnostic on/off switch, the yellow and red warning lights will come on and start flashing if any active fault code is recorded in the ECM. If both warning lights remain on and do

not flash, there are no active fault codes present.

NOTE: The equipment

must be stationary. If road speed is detected, the flashing sequence will

not occur.

The cruise control selector switch is used to step through the fault codes being flashed out. Each fault code will continue to flash until the cruise control selector switch is used.

If INSITE™ is available, monitor the switch for proper operation. If

not, follow the troubleshooting procedures in this section.

Locate the desired on/off toggle switch. Remove and tag the two connectors from the switch terminals. Touch the multimeter probes to the terminals on the switch.

Move the switch to 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 has failed.

Refer to the OEM troubleshooting and repair manual for the replacement instructions.

Move the switch to the ON position and measure the resistance. The multimeter

must show a closed circuit (10 ohms or less). If the circuit is

not closed, the switch has failed. 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.

Touch one of the multimeter probes to one of the switch terminals. Touch the other probe to chassis ground. Move the switch to the ON 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.