Cummins ISM Code 187 documents the Sensor 5-Volt Supply Circuit Low diagnostic and troubleshooting procedure for the Cummins ISM CM570 (1999-02) engine platform. This 11-page fault code sheet from TruckFaultCodes.com (Copyright 2017) covers fault code 187 (PID S232, SPN 620, FMI 4/4, YELLOW lamp) and the checks used to confirm and clear it.
Official document details
| Brand | Cummins |
|---|---|
| Model coverage | ISM CM570, ISX CM570, Signature CM570 (1999-02) |
| System / Group | Diagnostic Trouble Codes (DTCs) |
| Fault code | 187 — PID S232, SPN 620, FMI 4/4 |
| Warning lamp | YELLOW |
| Pages | 11 |
| File size | 0.5 MB |
| Format | |
| Language | English |
Document table of contents
- Circuit description
- Component location
- Shop talk
- Troubleshooting steps
- Fault code verification and clearing
Cummins ISM Code 187 diagnostic steps
The ECM supplies each sensor with +5 VDC. Low voltage on this supply can come from a short circuit to ground in a supply line, a short between a supply and return line, a failed sensor, or a failed ECM power supply. This eleven-page procedure covers the fuel rail pressure, fuel inlet restriction, oil pressure/temperature, wet tank pressure, coolant level, and Top 2 transmission position sensors, isolating the shorted line before the code is cleared.
Applicable truck models
This sheet applies to Cummins ISM CM570, ISX CM570, and Signature CM570 (1999-02) engines built around the CM570 ECM and the sensor voltage supply. It covers the fuel rail pressure, fuel inlet restriction, oil, wet tank, coolant level, and Top 2 transmission position sensors. The document is laid out with a circuit description, a component location note, shop-talk tips, and a step-by-step troubleshooting chart whose go-to branches route the technician through each measurement. Refer to the official Cummins engine support site for wiring diagrams and component part numbers.
Who needs this Cummins ISM Code 187 manual
Heavy-duty diesel technicians, fleet service teams, and owner-operators diagnosing a yellow-lamp sensor voltage supply fault will use this sheet to follow the factory decision tree, confirm the reading, and repair the harness, connector, or component instead of replacing parts on guesswork. It spells out each measurement threshold and its pass or fail branch, so the fault can be verified active, the repair validated, and the inactive code cleared with the diagnostic tool.
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