Cummins ISM Code 387 is the official Cummins fault code troubleshooting PDF that documents the throttle voltage supply on ISM CM570 (1999-02) engines. This 4-page reference from the Cummins service literature explains the circuit, the likely causes behind the yellow warning lamp, and the step-by-step checks a technician follows to confirm the repair.
Official document details
| Brand | Cummins |
|---|---|
| Model coverage | ISM CM570, ISX CM570 and Signature CM570 (1999-02) |
| System / Group | Throttle Voltage Supply (DTCs) |
| Fault code | Code 387 · PID P221 · SPN 1043 · FMI 3/3 |
| Warning lamp | Yellow |
| Year / Revision | Copyright 2017 |
| Pages | 4 |
| File size | 0.3 MB |
| Format | |
| Language | English |
Document table of contents
- Circuit description
- Component location
- Shop talk – possible causes
- Troubleshooting steps
- Fault code verification and clearing
Cummins ISM Code 387 troubleshooting summary
The ECM supplies the throttle and remote throttle with (+) 5 VDC. If the supply line to the throttles is damaged, the throttle will not work correctly. The throttle pedal is located in the cab. The manual walks through 6 labelled troubleshooting steps that inspect connectors and pins, measure circuit resistance, and verify the fault code is inactive after the repair.
High voltage on the (+) 5-VDC supply line will be caused by a short
circuit to battery of the supply line or a short circuit between an
actuator and the supply line.
Referenced Cummins service tools and part numbers: 3824510.
Applicable truck models
This procedure applies to Cummins ISM CM570, ISX CM570 and Signature CM570 engines built in the 1999-02 range, as used in Class 8 highway trucks. Always confirm the exact engine dataplate before servicing. Full engine specifications and dealer support are available on the Cummins official website.
Who needs this Cummins ISM Code 387 manual
Heavy-duty diesel technicians, fleet service managers and independent workshop owners diagnosing a Code 387 on the throttle voltage supply rely on this document to follow the manufacturer procedure instead of guessing at parts. Because Code 387 shares its troubleshooting logic with the ISX CM570 and Signature CM570 platforms, a single PDF supports several Cummins engine families in the same workshop.
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