This Cummins lift pump troubleshooting document covers Fault Code 278 for the lift pump circuit on Cummins ISB CM550 applications. It explains how the ECM enables the lift pump during key-on, cranking, and engine running, then gives connector, resistance, short-circuit, voltage, and code-clearing checks.
Official Cummins lift pump document details
| Brand | Cummins |
|---|---|
| Model coverage | ISB CM550 (1990-94) |
| System/Group | DTCs; Lift Pump Circuit |
| Publication no. | Not specified in extract |
| Year/Revision | Unknown |
| Pages | 6 |
| File size | 0.3 MB |
| Format | |
| Language | English |
Document table of contents
- FAULT CODE: 278
- PID: P073
- SPN: 1075
- FMI: 11
- LIFT PUMP CIRCUIT
- DESCRIPTION
- COMPONENT LOCATION
- TROUBLESHOOTING STEPS
- Step 1A: Inspect engine harness and lift pump connectors
- Step 1B: Check the resistance of the lift pump
- Step 1C: Check for a short-to-ground in the lift pump
- Step 2A: Inspect engine harness and ECM connector pins
- Step 2B: Check for an open circuit in the lift pump supply pin
- Step 2B-1: Check for an open circuit in the OEM harness
- Step 2C: Check for a short circuit to ground
- Step 2D: Check for short circuit from pin-to-pin
- Step 2E: Perform lift pump override test and measure voltage
- Step 3A: Verify Fault Code 278 is inactive
- Step 3B: Clear inactive fault codes
Applicable truck models
This file applies to Cummins ISB CM550 engines listed in the source group as 1990-94 DTC coverage. The extract identifies the component as the lift pump mounted to the engine block on the intake side, toward the rear of the engine, and the procedure is limited to Fault Code 278 with PID P073, SPN 1075, and FMI 11. For manufacturer information, visit Cummins official website.
Who needs this Cummins lift pump manual
Workshop owners, diesel mechanics, and diagnostic technicians need this file when a Cummins ISB CM550 reports Fault Code 278 and the lift pump circuit must be checked before replacing parts. The steps focus on practical electrical checks: damaged pins, connector seals, pump resistance, shorts to ground, open circuits through harness pins, OEM harness continuity, ECM connector inspection, lift pump override testing, and final fault-code verification.
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