This Cummins intake air heater document is a fault code troubleshooting guide for Code 2556 on ISB, ISC, and ISL applications. It explains the intake air heater 1 circuit, the ECM diagnostic logic, likely causes, and guided checks using INSITE™ electronic service tool and a multimeter.
Official Cummins intake air heater document details
| Brand | Cummins |
|---|---|
| Model coverage | ISB, ISC, and ISL; file group lists ISB6.7 CM2150 (2007-09) |
| System/Group | ISB6.7 CM2150 (2007-09) / DTCs; Intake Air Heater 1 Circuit |
| Publication no. | Not shown in extract |
| Year/Revision | Last Modified: 20-Jul-2010 |
| Pages | 12 |
| File size | 0.3 MB |
| Format | |
| Language | English |
Document table of contents
- Overview
- Circuit Description
- Component Location
- Conditions for Running the Diagnostics
- FAULT CODE 2556
- Conditions for Setting the Fault Codes
- Action Taken When the Fault Code is Active
- Conditions for Clearing the Fault Code
- Shop Talk
- Associated Procedures
- Troubleshooting Steps
- Guided Step 1 – Check the fault codes.
- Guided Step 2 – Check the intake air heater relay and circuit.
- Guided Step 3 – Check the ECM and OEM harness.
- Guided Step 4 – Clear the fault code.
Applicable truck models
This file applies to Cummins ISB, ISC, and ISL engine diagnostics for Fault Code 2556, described as “Intake Air Heater 1 Circuit – Voltage Below Normal or Shorted to Low Source.” The file information also places it under ISB6.7 CM2150 (2007-09) DTCs. OEM relay location varies by manufacturer, so the document refers technicians to Procedure 100-002 (Engine Diagrams) for detailed component location views. For official manufacturer information, visit Cummins.
Who needs this Cummins intake air heater manual
This manual is for diesel mechanics, fleet shops, and workshop owners diagnosing an amber CHECK ENGINE light linked to SPN 729 FMI 4 on Cummins engines. It is useful when checking whether the intake air heater relay, relay supply wiring, OEM harness, ECM connector pins, or ECM calibration is causing a low-voltage or short-to-low-source fault.
The troubleshooting sequence starts with reading active or inactive codes using INSITE™ electronic service tool. It then checks relay connectors for loose, corroded, bent, broken, pushed-back, expanded, wet, dirty, or damaged terminals and connector shells. Later steps verify the circuit response after disconnecting and reconnecting the intake air heater relays, then measure resistance for pin-to-ground and pin-to-pin shorts in the OEM harness. The resistance specification shown for these harness checks is greater than 100k ohms. If testing points to the relay, the document directs replacement of the intake air heater relay using the OEM troubleshooting and repair manual. If wiring checks fail, it directs repair or replacement of the OEM harness under Procedure 019-071.
The guide also states the ECM illuminates the amber CHECK ENGINE light immediately when the diagnostic runs and fails, and disables the intake air heater circuit. Clearing guidance includes starting the engine, idling for 1 minute, verifying that Fault Code 2556 is inactive, and clearing inactive fault codes with INSITE™ electronic service tool.
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