Cummins fault code 338 is the Cummins ISM CM871 (2007-09) diagnostic reference for Idle Shutdown Vehicle Accessories Relay Driver Circuit – Voltage Above Normal, or Shorted to High Source, reported as PID S087, SPN 1267, FMI 3/3 with an Amber lamp. This 5-page workshop PDF covers the Idle Shutdown Vehicle Accessories Relay Driver Circuit (ISX and ISM), giving the fault description, shop-talk notes, component location and the step-by-step troubleshooting tree. It is compiled from the TruckFaultCodes.com fault-code library (Copyright © 2017).
Official document details — Cummins fault code
| Brand | Cummins |
| Model coverage | ISM and ISX CM871 (2007-09) engines |
| System / Group | Idle Shutdown Vehicle Accessories Relay Driver Circuit (ISX and ISM) / DTCs |
| Fault identifiers | PID S087, SPN 1267, FMI 3/3, Amber lamp |
| Source | TruckFaultCodes.com fault-code library (© 2017) |
| Pages | 5 |
| File size | 0.28 MB |
| Format | |
| Language | English |
Document table of contents
- Fault code header (PID, SPN, FMI, lamp)
- Description
- Shop Talk
- Component Location
- Troubleshooting Steps
Reading Cummins fault code 338
When the idle shutdown accessory relay parameter is set to Installed, the ECM energizes the relay to switch off vehicle accessories during idle shutdown; the ECM monitors the circuit and records the code when it reads voltage while the signal is commanded off.
The Cummins Shop Talk section advises confirming the ECM calibration is correct and recalibrating if necessary. Documented possible causes include:
- the ECM Idle Shutdown feature set up incorrectly
- an open circuit in the idle shutdown relay, OEM harness or connectors
- a short circuit to a voltage source in the OEM harness or relay
Component location manual information
The idle shutdown relay location varies by OEM; refer to the OEM service literature.
Applicable truck models
This document applies to Cummins ISM CM871 (2007-09) engines, and the same circuit description is shared with the ISX CM871 platform where noted in the extract. These engines power many Class 8 highway tractors and vocational trucks built by North American OEMs. Confirm the exact ECM calibration and OEM wiring against the manufacturer records; full engine support is published by Cummins official engine support.
Who needs this Cummins fault code 338 manual
Fleet technicians, independent diesel mechanics and workshop owners diagnosing an active idle shutdown relay driver condition will use this sheet to follow the correct troubleshooting order instead of replacing parts on guesswork.
The full PDF is available in the DiagTechPro manuals library; a free account is required to download it.
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