Case IH P33 – Engine Management Unit (EMU) or Transmission/EDC (Electronic Diesel Control) controller: Boost Air Pressure Sensor, Shorted To Low Source

The Boost Air Pressure Sensor circuit is shorted to a low source (ground), meaning the signal voltage returning to the ECU has dropped below the minimum expected threshold.

• MXM
• MXM 120
• MXM 130
• MXM 140
• MXM 155
• MXM 175
• MXM 190
• TM Series
• Magnum
• Steiger

1. 1

   Visual Inspection: Locate the Boost Air Pressure Sensor on the intake manifold and inspect the wiring harness for chafing, melted insulation, or pinched wires touching the engine block or chassis.

2. 2

   Connector Check: Disconnect the sensor plug and look for moisture, dirt, or corroded pins bridging the signal wire to the ground wire.

3. 3

   Isolate the Sensor vs. Wiring: With the sensor disconnected, turn the key ON and check active codes. If it changes to T32, the sensor is internally shorted. If it remains T33/P33, the signal wire is shorted to ground.

4. 4

   Voltage Check: Using a multimeter, verify the sensor receives a 5V reference voltage and has a clean ground from the ECU.

1. 1

   Power Down

   Turn off the tractor, remove the key, and engage the parking brake.

2. 2

   Access the Sensor

   Open the hood and locate the Boost Air Pressure Sensor on the intake manifold piping (post-turbocharger).

3. 3

   Repair Wiring

   If the wiring is damaged: Splice and repair the shorted section of the wiring harness using weather-sealed heat-shrink connectors, or replace the damaged harness section. Route the harness away from high-heat or high-vibration areas.

4. 4

   Replace Sensor

   If the sensor is faulty: Remove the retaining bolts/screws holding the sensor to the manifold. Carefully pull the sensor out (ensure the old O-ring comes out with it). Lubricate the O-ring on the new sensor with a tiny amount of clean engine oil, press it into place, and secure the fasteners.

5. 5

   Reconnect

   Plug the electrical connector back into the sensor until it clicks.

6. 6

   Clear Codes

   Enter the tractor's H-Menu (diagnostic menu) via the instrument cluster to clear the stored fault codes.

7. 7

   Test

   Start the engine and monitor the display. Rev the engine to build slight boost pressure and verify that code T33 does not return.