Cumminz

Cummins ISB CM550 (1990-94) Fault Code: 599 PID: SID 025 SPN: 640 FMI: 14 Auxiliary Commanded Dual Output Shutdown – Special Instructions

Circuit Description
Dual outputs based on sensed parameters provide up to two independent switched outputs for
original equipment manufacturer (OEM) use. The state of each switched output can be
determined by different inputs to the engine control module (ECM) depending on the engine
platform. The ECM can provide different outputs to OEM devices if any of the inputs are above
or below calibrated thresholds. Each switched output is independent of the other with respect
to control parameter input and threshold settings.

Component Location
The dual outputs features are OEM dependent. Use the following for a detailed component
location view. See equipment manufacturer service information.

Shop Talk
This fault code is activated when one of the OEM defined inputs has exceeded a calibratible
limit. The triggers for shutdown are OEM dependent.

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Cummins ISB CM550 (1990-94) Fault Code: 768 PID: SID 009 SPN: 923 FMI: 11 Output Device Driver (Trransmission Shift Modulation)

Circuit Description
The output device driver is a device used by the electronic control module (ECM) to control the
transmission shift modulation signal.

Component Location
Refer to an OEM diagram for the location of the transmission shift modulator.

Shop Talk
Output device driver could be malfunctioning due to a failed engine harness, a bad ground on the
transmission shift modulator connector, or a bad transmission shift modulator.

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Cummins ISB CM550 (1990-94) Fault Code: 779 PID: SID 051 SPN: 703 FMI: 11 OEM Input – Engine Protection

Circuit Description
The OEM device input to engine protection allows vehicle OEMs to wire up a device, such as a
hydraulic oil temperature limit switch, transmission temperature limit switch, etc., to the ECM.
Some units have been upfitted with a Fuel Pressure Switch. The ECM will monitor values from
this device the same as other engine protection inputs, such as coolant level, etc.. If a
threshold value is exceeded, engine speed derate will occur and possible engine shutdown.

Component Location
The location of the OEM device is dependent upon the OEM. If the unit has a fuel pressure
switch installed, it is located at the fuel filter outlet.

Shop Talk
The fuel pressure switch is normally closed and grounds through the fuel filter housing. The
switch actuates (opens) at 24 kPa [3.5 psi]. Engine speed must be above 500 rpm before the switch input is recognized by the ECM. The switch is wired to pin “U” of the 23-pin connector
which goes to pin 15 of the ECM connector.

1) Sterling and Ford applications use a 16-pin OEM connector instead of a 23-pin. In
this case the fuel pressure switch is wired directly to pin 15 of the ECM connector.

Fault Code 779 will log anytime pin 15 of the ECM connector has continuity to ground when
the engine is above 500 rpm.

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