Case IH P84 – PCU (Powertrain Control Unit): RAM in PCU, data valid but below normal range

This code indicates a memory error within the Random Access Memory (RAM) of the Powertrain Control Unit. It means the controller's non-volatile memory has experienced a fault, lost its stored parameters, or has been reset, resulting in data that falls below the expected normal operating range.

• 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

   Verify power supply and ground circuits to the PCU, as voltage drops or bad grounds can cause the RAM to lose its memory or initialize incorrectly.

2. 2

   Check for accompanying codes such as T85, F24, or E24, which indicate that the transmission/EDC calibration has been lost and a recalibration is required.

3. 3

   Attempt a full transmission calibration to see if the PCU can successfully rewrite and hold the memory parameters.

1. 1

   Transmission Calibration

   Park the tractor on level ground, lower all equipment to the ground, place all shift levers in neutral, and block the front and rear wheels.

2. 2

   Transmission Calibration

   Press and hold the High and Low range buttons simultaneously, then start the engine.

3. 3

   Transmission Calibration

   Release the buttons when 'CAL' appears on the transmission display.

4. 4

   Transmission Calibration

   Set the engine speed to 1200 ERPM (± 100 RPM).

5. 5

   Transmission Calibration

   Follow the on-screen prompts to cycle through the clutch and synchronizer calibration.

6. 6

   Transmission Calibration

   If the calibration completes successfully, the display will show code CF (Calibration Procedure Completed Successfully). Turn the key off to save the data.

7. 7

   PCU Replacement

   If the calibration fails, or if the T84 code immediately returns after a key cycle, the microprocessor's internal RAM has physically failed. Disconnect the tractor's battery.

8. 8

   PCU Replacement

   Locate the PCU (Transmission Control Module) and disconnect the main wiring harnesses.

9. 9

   PCU Replacement

   Remove the mounting hardware and extract the faulty PCU.

10. 10

    PCU Replacement

    Install the replacement PCU and reconnect the harnesses.

11. 11

    PCU Replacement

    Reconnect the battery.

12. 12

    PCU Replacement

    Crucial: A newly installed PCU will be blank or uncalibrated. You must perform the full Transmission/EDC Calibration procedure immediately after installation.