Case IH P31 – Engine Controller (ECU): Boost Air Pressure Sensor, Grounded Or Current Above Normal Range

The Engine Control Unit (ECU) is detecting a voltage signal from the boost air pressure sensor (MAP sensor) that is either completely shorted to ground (0 volts) or drawing a current that exceeds the normal operating threshold. This prevents the ECU from accurately reading the intake manifold boost pressure, which can lead to torque reduction or engine derating.

• MXM
• MXM 120
• MXM 130
• MXM 140
• MXM 155
• MXM 175
• MXM 190
• TM120
• TM190
• Maxxum
• Puma
• T6 Series

1. 1

   Inspect the wiring harness leading to the Boost Air Pressure Sensor for chafing, melting, or bare wires that could be shorting against the engine block.

2. 2

   Disconnect the sensor and check the pins for corrosion, moisture, or bent terminals.

3. 3

   Using a multimeter, check the signal wire between the sensor connector and the Engine Controller for continuity to ground. If grounded while disconnected at both ends, repair the harness.

4. 4

   Verify that the sensor is receiving the correct 5V reference voltage from the ECU.

5. 5

   Ensure there are no massive boost leaks in the turbocharger or intercooler piping that could cause abnormal intake air pressure readings.

1. 1

   Turn off the tractor, remove the key, and allow the engine to cool.

   Ensure the machine is safe to work on before starting the repair.

2. 2

   Locate the Boost Air Pressure Sensor on the intake manifold.

   It is often located near the turbocharger air piping.

3. 3

   Depress the locking tab and disconnect the electrical connector from the sensor.

   Carefully remove the harness connection.

4. 4

   Remove the retaining bolt(s) securing the sensor to the manifold.

   Unbolt the sensor from its mounting location.

5. 5

   Carefully pull the sensor straight out.

   Remove the old sensor from the manifold.

6. 6

   Lubricate the O-ring on the new sensor with a small amount of clean engine oil.

   This prevents tearing the O-ring during installation.

7. 7

   Insert the new sensor into the manifold and tighten the retaining bolt to the specified torque.

   Secure the new sensor in place.

8. 8

   Reconnect the electrical harness until it clicks into place.

   Ensure a solid electrical connection.

9. 9

   Turn the key to the ON position and use the tractor's H-Menu or a diagnostic service tool to clear the stored T31/P31 fault code.

   Clear the fault code from the ECU memory.

10. 10

    Start the engine and verify that the code does not return.

    Confirm the repair was successful.