Case IH PE4 – Transmission/Tractor Electronic Controller (SCM/XCM or PCU): Fan speed signal error

The control module is not receiving a valid rotational speed signal back from the viscous fan drive coupling. This typically means that either the viscous drive coupler has burned out, the fan speed sensor has failed, or there is a fault/short in the wiring harness connecting the fan to the controller. (Note: Often misread as PE4 due to display fonts).

• MXM
• MXM 120
• MXM 130
• MXM 140
• MXM 155
• MXM 175
• MXM 190

1. 1

   Visual Loom Inspection: Trace the wiring loom from the viscous fan around the radiator cowl. Look for physical damage, rubbing, or melted wires.

2. 2

   5V Reference Check: Check the 5V reference line on the sensor harness for a short to ground, which is a common cause of this code.

3. 3

   Continuity Test: Disconnect the harness and check for a good ground on pin 4 of the harness side. Check for continuity between pin 3 and the fan controller (Pin 31 on MXM120-155 models, or Pin 27 on MXM175-190 models).

4. 4

   Audible Diagnostic Confirmation: Connect the diagnostic switch to the red SCM connector (C342). Turn the key on (do not start) and wait 30 seconds. If you hear one long tone followed by 7 short tones, it confirms the TE4 Fan Speed Signal Error (no signal coming back from the coupling).

1. 1

   Power Down

   Fully power off the machine, remove the key, and ensure safety locks are in place before working near the radiator.

2. 2

   Access the Fan

   Remove the fan cage/shroud to gain access to the viscous fan clutch and sensor assembly.

3. 3

   Remove the Faulty Component

   Unplug the electrical connector from the fan speed sensor. If replacing just the sensor, unbolt it from its mounting bracket. If the viscous coupling is burned out (very common when this code is thrown), unbolt the entire viscous fan drive assembly from the water pump (note: threads may be left-handed).

4. 4

   Installation

   Install the new sensor or viscous clutch assembly. If installing a standalone sensor, ensure the correct sensor gap is set (approximately 1/8”) so it can properly read the rotational speed without striking the moving parts.

5. 5

   Reassembly

   Tighten all hardware carefully (do not overtighten the sensor bracket) and reinstall the fan cage/shroud.

6. 6

   Testing

   Start the tractor and run the A/C to build head pressure (over 260 PSI), or allow the engine/transmission to reach operating temperature. The fan should engage, and the TE4 code should clear.