Case IH 3968 – Engine ECU (ISM-DI): Incorrect Injector Codes

The Engine Control Module (ECM) has detected that the fuel injector trim codes (also known as IQA, QR, or calibration codes) programmed into its memory are incorrect, invalid, or missing.

• skid steer
• Steiger series tractors
• Magnum series tractors
• SSL (Skid Steer Loaders)
• CTL (Compact Track Loaders)
• Combines (late 23xx and 25xx series)

1. 1

   Verify if the Engine ECU was recently replaced, flashed, or reprogrammed, which could have wiped the existing injector memory.

2. 2

   Verify if any fuel injectors were recently replaced by a technician who failed to program the new trim codes into the ECM.

3. 3

   Physically inspect the fuel injectors to locate the stamped trim codes (usually found stamped on the solenoid, printed on the top plastic housing, or on a parts sticker on the injector body).

4. 4

   Ensure the codes on the injectors are legible. If they are covered in soot or oil, clean the injector thoroughly with brake cleaner and use good lighting to read them.

5. 5

   Use a diagnostic scanner to read the live data and verify which cylinder's programmed code in the ECM does not match the physical injector installed in the engine.

1. 1

   Record the Codes

   Note the exact alphanumeric trim code (or scan the QR code) printed on each fuel injector. Carefully record which specific engine cylinder each injector is installed in, as mixing up the locations will cause the engine to run poorly.

2. 2

   Connect Diagnostic Tool

   Connect a compatible dealer-level diagnostic scan tool (such as the CNH Electronic Service Tool, Cummins Insite, or Jaltest) to the machine's diagnostic connector.

3. 3

   Access the ECM

   Navigate to the Engine Control Module (ISM-DI) calibration, programming, or "Injector Quantity Adjustment" (IQA) menu.

4. 4

   Input the Trim Codes

   Input the correct trim code for each specific cylinder position exactly as it appears on the injector.

5. 5

   Save and Relearn

   Save the new parameters to the ECM. Perform any required ECM "relearn" or reset procedures as prompted by the diagnostic software.

6. 6

   Clear the Fault

   Clear the 3968 fault code from the system.

7. 7

   Test Run

   Cycle the ignition and run the engine under load to verify the code does not return and that the engine runs smoothly.