Case IH t68 – PCU (Powertrain Control Unit): Main Relay Defect, Data Valid But Above Normal Range

This code indicates an issue with the main power relay circuit. The controller is receiving a valid data signal from the relay circuit, but the value (likely voltage or duration) is higher than the expected normal range. This typically means the relay is sticking closed (shutting off too late), the contacts are welded together, or there is a short to a high-voltage source in the relay control circuit.

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

1. 1

   Perform a relay swap test by swapping the main relay with another identical 5-pin relay from a non-critical circuit (like a work light relay) to see if the code clears.

2. 2

   Inspect the main relay socket terminals for melted plastic, scorch marks, or green corrosion which can cause high resistance or shorting.

3. 3

   Use a multimeter to check the wiring harness between the main relay socket and the PCU for a short to battery (voltage present on the switched wire when the key is off).

1. 1

   Disconnect Power

   Turn off the ignition and disconnect the negative battery cable to prevent electrical spikes.

2. 2

   Locate the Relay

   Access the main fuse and relay electrical center (refer to the operator's manual for the exact panel location, usually in the right-hand cab console).

3. 3

   Remove the Faulty Relay

   Pull the main power relay straight out of its socket.

4. 4

   Clean the Contacts

   If the socket pins are dirty or slightly oxidized, clean them with electrical contact cleaner and let them dry.

5. 5

   Install the New Part

   Plug the new 5-pin relay into the socket, ensuring it is seated firmly.

6. 6

   Reassemble and Test

   Reconnect the negative battery cable. Turn the ignition key to the "ON" position.

7. 7

   Clear Codes / Calibrate

   Verify that the t68 code is no longer active on the dash display. You may need to enter the tractor's H-Menu to clear stored inactive codes or perform a basic transmission calibration if the PCU memory was reset.