Case IH tAA – Pump Control Unit (PCU): PCU CAN Chip, Data Valid But Above Normal Range

Indicates a faulty connection or communication failure between the Engine Control Module (ECM) and the Pump Control Unit (PCU). When this code is active, the engine goes into a limp-home condition: fuel quantity is reduced, and engine speed is severely restricted to a maximum of 1300 RPM.

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

1. 1

   Ensure the tractor's power is OFF and the keyswitch is OFF. Disconnect the battery or pull the specified fuse to prevent electrical damage.

2. 2

   Disconnect the harness connectors at both ends of the circuit (at the ECM and the PCU) to prevent false readings.

3. 3

   Set a digital multimeter to measure resistance (ohms).

4. 4

   Inspect the connector pins for dirt, corrosion, or damage. Avoid touching the metal connector cases with the test leads.

5. 5

   Measure the circuit resistance of the CAN harness between the ECM and PCU. If the resistance is 3 to 4 ohms or less, the circuit is continuous. Higher resistance indicates dirty or corroded terminals, while a reading near 100K ohms indicates an open circuit in the wiring.

1. 1

   Power down the tractor and disconnect the battery.

2. 2

   Locate the Engine Control Module (ECM) and the Pump Control Unit (PCU), which is mounted to the fuel injection pump.

3. 3

   Disconnect the wiring harness at both modules.

4. 4

   Clean any dirty or corroded connector terminals using electrical contact cleaner.

5. 5

   Based on your multimeter continuity test, if there is an open circuit or high resistance in the harness, repair the damaged section of the CAN wiring or replace the harness entirely.

6. 6

   If the harness and connectors test perfectly, the fault may lie internally within the PCU or ECM CAN transceiver chips.

7. 7

   Reconnect all harnesses securely.

8. 8

   Reconnect the battery, turn the key on, and use an electronic service tool to clear code 3012 / tAA.

9. 9

   Start the engine and verify that the 1300 RPM limp-mode restriction is lifted.