Case IH tD8 – PCU (Power Control Unit): PCU Power Supply, Data Valid But Above Normal Range

Indicates an overvoltage condition where the control module receives a power supply voltage that exceeds the maximum acceptable threshold, commonly caused by a failing alternator voltage regulator or a wiring harness short.

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

1. 1

   Perform a battery voltage test with the engine off to ensure a baseline of around 12.6V.

2. 2

   Test alternator output with the engine running by measuring voltage at the battery and PCU power supply pin. Spikes above 14.5V - 15V indicate a faulty voltage regulator overcharging the system.

3. 3

   Inspect the wiring harness routing to the PCU for chafed wires that might be shorting the power supply circuit to a higher voltage source.

4. 4

   Verify that the PCU ground connections are clean and tight, as poor grounds can cause voltage reference irregularities.

1. 1

   Disconnect Power

   Disconnect the negative battery cable before performing any electrical repairs.

2. 2

   Address the Overvoltage Source

   If the alternator is overcharging, remove the drive belt and unbolt the alternator to install a new one (or replace the internal voltage regulator). If a wiring short was found, splice and repair the damaged section using weather-sealed connectors.

3. 3

   Reconnect and Verify

   Reconnect the battery, start the tractor, and verify that the system voltage remains within the normal operating range (approx. 13.5V - 14.2V).

4. 4

   Clear Codes and Calibrate

   Use the tractor's H-Menu diagnostic interface to clear the tD8 fault code, and perform a Transmission/EDC Calibration (Routine 1) if shift quality has deteriorated or if the non-volatile memory was reset.