Case IH t33 – Engine Management Unit (EMU): Boost Air Pressure Sensor, Shorted To Low Source.

The engine controller is receiving a signal voltage from the boost air pressure (MAP) sensor that is below the acceptable minimum threshold. This typically indicates that the sensor's signal wire is shorted to ground, there is an open circuit in the wiring harness, or the sensor itself has failed internally.

• MXM
• MXM120
• MXM130
• MXM140
• MXM155
• MXM175
• MXM190

1. 1

   Visually inspect the wiring harness leading to the boost air pressure sensor for chafed insulation, pinched wires, or melted sections that could cause a short to ground.

2. 2

   Disconnect the 4-pin connector from the sensor and check for water ingress, corrosion, or bent pins that could bridge the signal wire to the ground wire.

3. 3

   Turn the key to the ON position (engine off) and use a multimeter to verify that the sensor is receiving the correct 5V reference voltage and has a solid ground at the harness connector.

4. 4

   Check the signal wire for continuity back to the Engine ECU and ensure it is not shorted to the chassis ground. If wiring passes all tests, the sensor is internally shorted.

1. 1

   Park the tractor on a level surface, turn off the engine, and remove the key to de-energize the Engine ECU.

2. 2

   Locate the boost air pressure sensor on the engine's intake air system.

3. 3

   Depress the locking tab and carefully disconnect the 4-terminal electrical connector from the sensor.

4. 4

   Remove the two mounting bolts securing the sensor to the manifold.

5. 5

   Pull the old sensor straight out.

   Clean the mounting surface and ensure no debris falls into the intake.

6. 6

   Insert the new boost air pressure sensor and secure it with the two mounting bolts.

7. 7

   Reconnect the 4-terminal electrical harness until it clicks into place.

8. 8

   Turn the ignition key to the ON position.

   Access the tractor's "H-Menu" (diagnostic display) to clear the stored t33 fault code.

9. 9

   Start the engine and verify that the code does not return and that the tractor operates without derating.