This Cummins ISB6.7 misfire code document covers Fault Code 1656 for an engine misfire condition on cylinder number 3. The PDF explains how the ECM detects cylinder contribution changes, when the amber CHECK ENGINE lamp or MIL can illuminate, and what checks are used to confirm or clear the fault. It is a short diagnostic reference for ISB6.7 CM2350 engines in the 2013-17 DTC group.
Official Cummins ISB6.7 misfire code document details
| Brand | Cummins |
|---|---|
| Model coverage | ISB6.7 CM2350, 2013-17 DTC coverage |
| System/Group | DTCs; Engine Misfire Cylinder 3 – Condition Exists |
| Publication no. | Fault Code 1656; SPN 1325; FMI 11/31 |
| Year/Revision | Unknown; copyright 2017 in source extract |
| Pages | 5 |
| File size | 0.1 MB |
| Format | |
| Language | English |
Document table of contents
- Fault Code: 1656
- PID, SPN: 1325, FMI: 11/31, LAMP: Amber
- Engine Misfire Cylinder 3 – Condition Exists
- Circuit Description
- Component Location
- Reason
- Conditions for Running the Diagnostics
- Conditions for Setting the Fault Codes
- Action Taken When the Fault Code is Active
- Conditions for Clearing the Fault Code
- Shop Talk
- Troubleshooting Steps
- Step 1A) Read the fault codes
- Step 1B) Check for cylinder misfire
- Step 2A) Perform the cylinder cutout test
- Step 3A) Check if an ECM calibration update is available
- Step 3B) Disable the fault code
Applicable truck models
This file applies to Cummins ISB6.7 CM2350 engines listed under the 2013-17 DTC group. The extract does not name truck makes or chassis models, and the ECM mounting location is stated as variable depending on engine model, either on or off the engine. The diagnostic is for Fault Code 1656, SPN 1325, FMI 11/31, where the ECM detects cylinder 3 misfire while monitoring engine speed as each injector fires. For official engine and service information, visit Cummins.
Who needs this Cummins ISB6.7 misfire code manual
Mechanics, fleet technicians, and workshop owners need this manual when an ISB6.7 CM2350 has an amber lamp, low power complaint, rough idle, smoke, engine stumble, or a stored cylinder 3 misfire fault. The procedure helps separate inactive intermittent events from active problems that need injector, valve lash, cylinder, valve, head gasket, camshaft, air compressor timing, or ECM calibration checks.
The troubleshooting path starts by reading fuel system fault codes with a diagnostic tool, then checking for smoke, stumble, rough idle, or misfire at low idle, high idle, and snap throttle acceleration. If a misfire is present, the Cylinder Cutout Test is used to determine whether the cylinder number 3 injector is involved. If the malfunction follows the injector diagnosis, the document directs replacement of the cylinder number 3 injector; otherwise it points to other mechanical misfire sources. It also explains that EGR valve operation is disabled when the fault is active and that torque may be reduced if operation continues for an extended period. The Cummins ISB6.7 misfire code repair is validated by idling the engine for up to 5 minutes until the diagnostic runs and passes, then confirming the fault status changes to inactive.
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