Case IH 26 – Transmission ECM: Engine RPM Frequency Signal Too High

The Engine RPM signal registers as greater than 3500 RPM for 3 consecutive seconds while the Wheel Speed Sensor indicates movement and a transmission clutch pack is receiving full pressure.

• JXC
• JX55
• JX60
• JX65
• JX70
• JX75
• JX80
• JX85
• JX90
• JX95
• JX100U
• Magnum 245
• Steiger 500
• TG215
• TG245
• TN60A
• TN70A
• TN75A
• TN85A
• TN95A

1. 1

   Check alternator drive belt tension for wear, glazing, or looseness (should deflect 10 to 11 mm when 78 to 98 N of force is applied).

2. 2

   Verify engine high idle settings are within factory specifications and the engine is not over-revving.

3. 3

   Inspect the wiring harness between the Alternator W+ terminal and Transmission ECM connector 2, pin 15 for an open circuit, short to ground, or short to 12V.

4. 4

   Perform an ECM Channel Test using a diagnostic tool on H9, channel 20 to see if the value is registering higher or lower than the specified threshold.

1. 1

   Disconnect Power

   Always disconnect the negative battery cable before working on the electrical system or alternator.

2. 2

   Adjust or Replace the Drive Belt

   If the belt is loose but in good condition, slacken the nut securing the alternator, apply tension until the 10-11 mm deflection is achieved, and retighten the nut. If the belt is worn or broken, remove the old belt, route the new belt over the coolant pump and alternator pulleys, and tension it to the exact specification above.

3. 3

   Repair Wiring

   If the diagnostic checks revealed a short or open circuit in the W+ tachometer signal wire, splice in a repair wire or replace the damaged section of the harness between the alternator and the ECM.

4. 4

   Replace the Alternator

   Disconnect the wiring harness from the rear of the alternator (noting the W+ terminal location). Remove the mounting bolts and the drive belt. Install the new alternator, reattach the mounting bolts loosely, install the belt, apply proper tension, and tighten the bolts. Reconnect the wiring harness and the battery.

5. 5

   Clear Codes

   Clear the fault codes from the Transmission ECM and test drive the tractor to ensure the clutch pack engages properly and the code does not return.