This code 338 DTCs document is a troubleshooting PDF for the idle shutdown vehicle accessories relay driver circuit. It explains the circuit description, fault conditions, ECM response, INSITE™ checks, relay testing, OEM harness inspection, calibration review, and clearing steps for Code 338.
Official code 338 DTCs document details
| Brand | Cummins |
|---|---|
| Model coverage | ISB6.7 CM2250 (2010-12) / extract also references ISX11.9 CM2250, ISX15 CM2250, and ISM11 CM876 associated procedures |
| System/Group | DTCs; Idle Shutdown Vehicle Accessories Relay Driver Circuit |
| Publication no. | Not shown in the extract; associated bulletin numbers include 4022196, 4022250, and 2883445 |
| Year/Revision | Unknown; last modified dates shown are 11-Jun-2010 and 20-Jul-2010 |
| Pages | 13 |
| File size | 0.2 MB |
| Format | |
| Language | English |
Document table of contents
- Overview
- Circuit Description
- Component Location
- Conditions for Running the Diagnostics
- FAULT CODE 338 – Idle Shutdown Vehicle Accessories Relay Driver Circuit – Voltage Above Normal or Shorted to High Source
- 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 and electronic setting.
- Guided Step 2 – Check the idle shutdown relay and circuit.
- Guided Step 3 – Check the ECM and OEM harness.
- Guided Step 4 – Check ECM calibration and clear fault codes.
Applicable truck models
The file information lists Cummins ISB6.7 CM2250 (2010-12) DTC coverage, while the sampled pages identify ISX11.9 CM2250/ISX15 CM2250 idle shutdown relay diagnostics and associated procedures for ISM11 CM876, ISX15 CM2250, and ISX11.9 CM2250. The procedure is OEM-dependent because the idle shutdown relay location and relay return circuit can vary by vehicle manufacturer, with the return routed either through ECM Return (General) or directly to ground. See Cummins official website.
Who needs this code 338 DTCs manual
Workshop technicians, fleet mechanics, and diagnostic specialists need this manual when an amber CHECK ENGINE light is linked to SPN 1267 FMI 3/3 and accessories controlled by the idle shutdown relay do not power up. It supports checks with the INSITE™ electronic service tool, resistance tests, connector inspection, OEM harness repair decisions, ECM calibration review, and possible ECM replacement authorization.
The troubleshooting flow starts by checking active or inactive fault codes and verifying whether the Shutdown Accessory Relay parameter is set to “Installed” or “Not Installed” to match the vehicle. It then directs inspection of the idle shutdown relay and connector pins for corrosion, bent pins, moisture, damaged seals, debris, wire insulation damage, and locking tab damage. Electrical checks include relay resistance, return circuit continuity below 10 ohms, open circuit checks in the OEM harness, and pin-to-pin short checks where resistance should be greater than 100k ohms. If connector removal corrects the fault, no repair is required; if the fault remains after harness checks, the document directs authorization before replacing the ECM under Procedure 019-031. The final section checks whether an ECM calibration update is available under Procedure 019-032, then uses operating conditions from the summary section to confirm the fault code becomes inactive.
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