Case IH P68 – PCU (Powertrain Control Unit) / Transmission Controller: Main Relay Defect, Data Valid But Above Normal Range

The control module is receiving a valid signal from the main power relay circuit, but the voltage or current reading is higher than the expected operational threshold. This typically points to a failing relay with high internal resistance, a short to a high voltage source, or a wiring harness issue.

• MXM
• MXM120
• MXM130
• MXM140
• MXM155
• MXM175
• MXM190
• TM115
• TM120
• TM125
• TM130
• TM135
• TM140

1. 1

   Check the main harness-to-engine harness connectors (located beneath the front of the cab) for corrosion, moisture, or loose pins

2. 2

   Test the main relay in the electrical fuse/relay panel to see if it is sticking or has high internal resistance

3. 3

   Verify that the main system fuses (such as the 40A or 60A Maxi fuses) are intact and that their sockets are not melted or corroded

1. 1

   Disconnect Power

   Turn the key switch to the 'OFF' position and disconnect the battery to prevent electrical shorts.

2. 2

   Replace the Faulty Relay

   Remove the defective main relay from the fuse/relay board and install a new OEM replacement relay. Ensure the socket terminals are clean before inserting the new relay.

3. 3

   Clear the Fault Code

   Reconnect the battery. Enter the tractor's diagnostic 'H-Menu' by installing the diagnostic connector and turning the key switch to 'ON'. Clear the stored T68 fault code from the non-volatile memory.

4. 4

   Recalibrate the Transmission (If Necessary)

   If the non-volatile memory was reset or shift quality has deteriorated due to the electrical fault, perform a transmission calibration. Warm the transmission oil, set the engine speed to 1200 RPM, and use the High and Low range buttons to initiate the 'CAL' procedure until the clutch packs are fully recalibrated.