This Cummins CM550 374 document covers Fault Code 374, PID P1688, for a VP44 fuel pump calibration error. It explains when the code may set at key-on or while running, where the VP44 fuel pump is located, and how to test the power supply, ground, connectors, relay, fuses, and charging system before final verification.
Official Cummins CM550 374 document details
| Brand | Cummins |
|---|---|
| Model coverage | ISB CM550 (1990-94) |
| System/Group | DTCs; VP44 Fuel Pump |
| Publication no. | Not specified |
| Year/Revision | Unknown |
| Pages | 4 |
| File size | 0.3 MB |
| Format | |
| Language | English |
Document table of contents
- FAULT CODE: 374
- PID: P1688
- VP44 FUEL PUMP CALIBRATION ERROR
- VP44 Fuel Pump
- DESCRIPTION
- COMPONENT LOCATION
- TROUBLESHOOTING STEPS
- Step 1A) Turn key switch ON and check to see if fault code is active at engine start-up.
- Step 2A) Disconnect the engine harness from the fuel pump and measure supply voltage during cranking.
- Step 3A) Check the VP44 connector pins using inspection tool, Part Number 3164980.
- Step 4A) Install the VP44 fuel pump diagnostic tool, Part Number 3163834.
- Step 5A) Inspect harness, fuel pump, ECM connector pins, fuses, and relay.
- Step 6A) Check VP44 fuel pump supply resistance.
- Step 6B) Check VP44 fuel pump ground circuit resistance.
- Step 6C) Connect a 12-VDC headlight to pins 6 and 7 of the VP44 connector.
- Step 7A) Inspect engine, battery, and chassis ground connections.
- Step 7B) Inspect fuses and wires in the OEM distribution box.
- Step 7C) Remove the alternator belt and run engine to see if Fault Code 374 returns.
- Step 8A) Disable the fault code, road-test for 30 minutes, and verify Fault Code 374 is inactive.
Applicable truck models
This file applies to Cummins ISB CM550 engines from the 1990-94 coverage group with DTC information for Fault Code 374 and PID P1688. The extract identifies the VP44 fuel pump on the backside of the gear housing and gives diagnostic checks for the VP44 supply voltage, ground circuit resistance, connector condition, relay, fuses, OEM distribution box wiring, battery connections, chassis grounds, and charging system wiring. For official brand information, visit Cummins official website.
Who needs this Cummins CM550 374 manual
Workshop technicians, fleet mechanics, and diagnostic tool users need this Cummins CM550 374 manual when an ISB CM550 reports Fault Code 374 at engine start-up or while running. It is useful before replacing a VP44 injection pump because the steps call for electrical checks, connector inspection, relay and fuse inspection, a headlight load test, and a 30-minute road-test verification.
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