This 15-page PDF is a Cummins 1239 fault code troubleshooting guide covering Fault Code 1239 — Accelerator Pedal or Lever Position Sensor 2 Circuit, Voltage Above Normal or Shorted to High Source. It provides circuit descriptions, conditions for setting and clearing the code, shop talk notes, and a complete guided diagnostic procedure for engines equipped with the CM2250 electronic control module.
Official Cummins 1239 fault code document details
| Brand | Cummins |
| Model coverage | ISB6.7 CM2250, ISC8.3 CM2250, ISL9 CM2250, ISX15 CM2250, ISX11.9 CM2250, QSL9 CM2250, QSB6.7 CM2250, GX CM2250 |
| System / Group | Diagnostic Trouble Codes (DTCs) — Accelerator Pedal Position Sensor 2 |
| Publication no. | N/A (Bulletin 4022254 referenced for ISB6.7 CM2250) |
| Year / Revision | Last Modified 20-Jan-2011 |
| Pages | 15 |
| File size | 0.3 MB |
| Format | |
| Language | English |
Document table of contents
- Overview — Circuit Description (Hall-Effect accelerator pedal position sensor)
- Fault Code 1239 — Code, Reason, Effect (SPN 2623, FMI 3, Amber lamp, severe derate)
- Component Location
- Conditions for Running the Diagnostics
- Conditions for Setting the Fault Code
- Action Taken When the Fault Code is Active
- Conditions for Clearing the Fault Code
- Shop Talk — possible causes and wiring notes
- Associated Procedures Table (ECM Procedure 019-031, ECM Calibration Code Procedure 019-032)
- Guided Step 1 — Check fault codes and sensor supply fault codes
- Guided Step 2 — Check accelerator pedal position sensor supply voltage, return circuit, and circuit response (4.75-VDC to 5.25-VDC threshold)
- Guided Step 3 — Check ECM and OEM harness (pin inspection, open circuit below 10 ohms, pin-to-pin short above 100k ohms)
- Guided Step 4 — Check ECM calibration and clear fault codes
Applicable truck models
This document applies to vehicles equipped with Cummins CM2250 controllers across multiple engine platforms: ISB6.7, ISC8.3, ISL9, ISX15, ISX11.9, QSL9, QSB6.7, and GX. Additional CM2150 and CM2220 engine models such as ISF2.8, ISF3.8, ISB4.5, ISD4.5, ISD6.7, ISL8.9, ISM11, and ISZ13 are referenced in the associated procedures table. When the fault is active the ECM illuminates the amber CHECK ENGINE lamp and enforces a severe derate, limiting the engine to limp-home power only. For official technical resources visit Cummins technical documentation.
Who needs this Cummins 1239 fault code manual
Diesel mechanics, fleet maintenance technicians, and workshop owners diagnosing a DTC 1239 on CM2250-equipped Cummins engines need this guide. It walks through each diagnostic step using INSITE™ electronic service tool, multimeter resistance and voltage checks, and harness inspection procedures referenced to Section 19.
The full PDF is available in the DiagTechPro manuals library, free account required to download.
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