Case IH P29 – Engine Electronic Control Unit (EECU) or Vehicle Electronic Control Unit (VECU): Boost Air Temperature Sensor (PHY), Shorted To High Source

The engine control module is receiving a signal voltage from the boost air temperature sensor that is above the normal operating range. A "shorted to high source" condition typically indicates that the sensor's signal wire is shorted to a positive voltage source (B+), or there is an open circuit in the sensor/wiring that causes the controller's internal pull-up voltage to read at its maximum limit.

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

1. 1

   Visually inspect the wiring harness and connector at the Boost Air Temperature Sensor for chafing, melted insulation, or pinched wires.

2. 2

   Disconnect the sensor and check for water intrusion, corrosion, or bent pins inside the connector.

3. 3

   Test the sensor's resistance using a multimeter (e.g., 595 ohms at 60°C, 322 ohms at 80°C, and 186 ohms at 100°C). An open circuit or zero ohms indicates internal failure.

4. 4

   With the sensor disconnected and key ON, check the signal wire from the ECU. A reading of 12V instead of a 5V reference indicates a short to a high power source.

1. 1

   Power Down

   Turn off the tractor, remove the key, and disconnect the negative battery terminal to prevent electrical spikes during repair.

2. 2

   Locate the Sensor

   Locate the Boost Air Temperature Sensor on the engine's intake air piping or intake manifold.

3. 3

   Remove the Faulty Sensor

   Depress the locking tab on the electrical connector and pull it off the sensor. Use an appropriately sized deep socket or wrench to unthread the sensor from the manifold.

4. 4

   Install the New Sensor

   Thread the new OEM sensor into the port by hand to prevent cross-threading, then tighten it to the manufacturer's specified torque.

5. 5

   Reconnect

   Plug the electrical connector back into the sensor until it clicks securely. Reconnect the battery.

6. 6

   Clear Codes and Test

   Turn the key to the ON position. Use a diagnostic service tool or the tractor's onboard H-Menu (calibration/configuration menu) to clear the stored t29/P29 fault code. Start the engine and verify that the code does not return and that the engine operates without derating.