This document is a Cummins 377 fault troubleshooting sheet for the ISB CM550 fuel pump circuit. It explains Fault Code 377, PID S233, SPN 1077, FMI 7, and the condition described as FUEL PUMP POWER RELAY STUCK-ON. The procedure focuses on ECM logic, VP44 relay voltage checks, harness resistance checks, and final code clearing.
Official Cummins 377 fault document details
| Brand | Cummins |
|---|---|
| Model coverage | ISB CM550 (1990-94) |
| System/Group | DTCs; Fuel Pump Circuit |
| Publication no. | Not shown in the extract |
| Year/Revision | Unknown; Copywrite 2017 shown |
| Pages | 3 |
| File size | 0.3 MB |
| Format | |
| Language | English |
Document table of contents
- FAULT CODE: 377
- PID: S233
- SPN: 1077
- FMI: 7
- FUEL PUMP POWER RELAY STUCK-ON
- Fuel Pump Circuit
- DESCRIPTION
- COMPONENT LOCATION
- TROUBLESHOOTING STEPS
- Step 1A) Connector and pin inspection
- Step 1B) Short circuit from pin to pin resistance check
- Step 1C) VP44 voltage supply circuit external voltage check
- Step 2A) Stuck “ON” relay resistance check
- Step 3A) Verify that Fault Code 377 is inactive
- Step 3B) Clear the inactive fault codes using the diagnostic tool
Applicable truck models
This Cummins 377 fault file applies to Cummins ISB CM550 engines from the 1990-94 group as stated in the file information. The extract notes that some older ISB engines use a different OEM interface connector than illustrated, so connector identification must be checked against the truck harness before testing. The procedure covers the engine harness connector at the ECM, the fuel pump relay connector, the VP44 relay connector, and the fuel pump circuit logic internal to the ECM. See the manufacturer site at Cummins official website.
Who needs this Cummins 377 fault manual
Workshop technicians, mobile diesel mechanics, and fleet repair owners need this manual when a Cummins ISB CM550 logs Fault Code 377 after the key switch is turned off. It is also useful when checking for a stuck VP44 relay, unwanted voltage at pin 7 of the VP44 connector, damaged connector pins, moisture, missing seals, or engine harness shorts.
The procedure gives direct pass/fail decisions for resistance above 100k ohms, voltage less than 1.0 VDC, relay resistance between pin 30 and post 87, and final verification after the engine idles for one minute. Use it with an appropriate diagnostic tool to disable the fault code, confirm the code is inactive, and clear inactive fault codes after repairs. Full PDF available in the DiagTechPro manuals library, free account required to download.
Related manuals library
Sản phẩm liên quan cho hãng này
Cùng brand theo taxonomy hiện có trong catalog WooCommerce.
Cummins Calterm Version 5.16 – Advanced ECM Control and Precision Tuning for Cummins Engines
Cummins INSITE 9.3 – The Essential Diagnostic Tool for Cummins Engines
Cummins InCal CE – The Calibration and Configuration Tool for Cummins Engines
