This Cummins 381 fault code document is a 4-page diagnostic PDF for the intake air heater relay circuit on Cummins ISB CM550 applications. It identifies PID S237, SPN 626, and FMI 11, then gives step-by-step electrical checks for relay control, harness continuity, shorts, and final fault clearing.
Official Cummins 381 fault code document details
| Brand | Cummins |
|---|---|
| Model coverage | ISB CM550 (1990-94) |
| System/Group | DTCs; Intake Air Heater Relay Circuit |
| Year/Revision | Unknown |
| Pages | 4 |
| File size | 0.3 MB |
| Format | |
| Language | English |
Document table of contents
- FAULT CODE: 381
- PID: S237
- SPN: 626
- FMI: 11
- INTAKE AIR HEATER RELAY CIRCUIT
- DESCRIPTION
- COMPONENT LOCATION
- TROUBLESHOOTING STEPS
- Step 1A: Inspect the OEM harness, intake air heater relay, and ECM connectors
- Step 1B: Check for an open circuit in the relay enable circuit
- Step 1C: Check for an open circuit in the relay and relay ground
- Step 1D: Check for a short circuit to ground in the intake air heater relay circuit
- Step 1E: Check for a short circuit from pin to pin
- Step 1F: Check for a short circuit to battery
- Step 2A: Verify Fault Codes 381 are inactive
- Step 2B: Clear the inactive fault codes using the diagnostic tool
Applicable truck models
This file applies to Cummins ISB CM550 engines in the 1990-94 coverage group where Fault Code 381 is used for the intake air heater relay circuit. The extract states that the heater is located at the air inlet connection into the intake manifold, while heater relay location varies with the OEM, so truck placement depends on the chassis manufacturer. For current engine and support information, visit Cummins official site.
Who needs this Cummins 381 fault code manual
Workshop technicians, fleet mechanics, and electrical diagnosticians need this 381 fault code manual when an ISB CM550 shows an intake air heater relay circuit fault. The procedure focuses on connector condition, ECM connector pin 41, heater relay pin A, relay ground, resistance thresholds, voltage checks, and diagnostic-tool verification after repair.
The document also warns that these faults can indicate heater circuits shorted to battery positive, which can keep the grids on full time, drain batteries, burn out grids, or damage intake gaskets. The full PDF is available in the DiagTechPro manuals library, free account required to download.
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