This Cummins VP44 relay circuit document is a troubleshooting manual for Fault Code 391 on Cummins ISB CM550 engines. It explains the VP44 relay coil supply circuit, related voltage-dependent symptoms, connector inspections, resistance checks, voltage checks, and final fault-code verification.
Official Cummins VP44 relay circuit document details
| Brand | Cummins |
|---|---|
| Model coverage | ISB CM550 (1990-94) |
| System/Group | DTCs; VP44 relay coil supply circuit |
| Publication no. | Not stated in extract |
| Year/Revision | Unknown |
| Pages | 6 |
| File size | 0.5 MB |
| Format | |
| Language | English |
Document table of contents
- Fault Code: 391
- PID: S017
- SPN: 632
- FMI: 11
- VP44 Relay Coil Supply Circuit
- Description
- Component Location
- Troubleshooting Steps
- Step 1A: engine harness and ECM connector inspection
- Step 1B: battery voltage check
- Step 1C: fuel shutoff circuit open-circuit check
- Step 1D: relay ground circuit open-circuit check
- Step 1E: engine harness ground circuit check
- Step 1F: short circuit to ground check
- Step 1G: short circuit from pin to pin check
- Step 1H: ECM signal voltage check at VP44 relay connector
- Step 2A: VP44 power relay and engine harness inspection
- Step 2B: VP44 ground circuit resistance check
- Step 3A: disable fault code and verify Fault Code 391 inactive
- Step 3B: clear inactive fault codes using the diagnostic tool
Applicable truck models
This file applies to Cummins ISB CM550 engines in the 1990-94 coverage group where Fault Code 391, PID S017, SPN 632, FMI 11 is used for the VP44 relay coil supply circuit. The component location is supplied by the equipment manufacturer, so the document directs the technician to the OEM service manual for the vehicle-specific relay location. For manufacturer information, visit Cummins official website.
Who needs this Cummins VP44 relay circuit manual
Workshop owners, diesel mechanics, and electrical diagnostic technicians need this VP44 relay circuit manual when an ISB CM550 has Fault Code 391, possible Fault Code 364, or a no-start condition linked to high resistance or low voltage in the VP44 power supply circuit. It is most useful when checking ECM connector pins, OEM fuel shutoff wiring, relay ground paths, battery return, and VP44 connector pin 6 resistance.
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