Circuit Description
The ECM receives unswitched battery input through the engine harness. There are three inline
7.5-amp fuses and two 10-amp fuses in the unswitched battery wire of the actuator
harness to protect the engine harness from overheating.
Component Location
The ECM is connected to the battery by the engine harness. This direct link provides a
constant power supply for the ECM. The location of the battery will vary with the equipment
manufacturer. Refer to the equipment manufacturer’s repair manual for the battery location.
Shop Talk
Make sure the ECM unswitched battery supply is coming directly from the battery and not the
starter or other device. Check for possible weak batteries.
Cummins ISB CM550 (1990-94) Fault Code: 434 PID: SID 251 SPN: 627 FMI: 2 Unswitched Battery Supply Circuit
Cummins ISB CM550 (1990-94) Fault Code: 433 PID: 102 SPN: FMI: 2 Intake Manifold Pressure Sensor Circuit
Cummins ISB CM550 (1990-94) Fault Code: 432 PID: 91 SPN: 91 FMI: 13 Accelerator Pedal Circuit (ISS)
Cummins ISB CM550 (1990-94) Fault Code: 431 PID: 91 SPN: 91 FMI: 4 Idle Validation Switch (IVS) Circuit
Cummins ISB CM550 (1990-94) Fault Code: 431 PID: 91 SPN: 91 FMI: 2 Idle Validation Switch (IVS) Circuit
Cummins ISB CM550 (1990-94) Fault Code: 429 PID: 97 SPN: 97 FMI: 4 Water-In-Fuel (WIF) Sensor Circuit
