Case IH t29 – Electronic Engine Controller (ECU): Boost Air Temperature Sensor (PHY), Shorted To High Source

The engine control system has detected that the signal voltage from the Boost Air Temperature Sensor (also known as the Intake Manifold Air Temperature Sensor) is abnormally high. This typically indicates that the sensor's signal wire is shorted directly to a power source (such as a 5V reference or 12V battery voltage), or the sensor itself has failed internally and is bridging the power and signal circuits.

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

1. 1

   Visually inspect the Boost Air Temperature Sensor housing, connector, and wiring harness for physical damage, melted insulation, or rubbing against hot engine components.

2. 2

   Perform a disconnect test: Turn the key ON (engine OFF) and disconnect the sensor. If the code changes to t23, the sensor is internally shorted. If it remains t29, the short is in the wiring harness.

3. 3

   Check harness voltage: With the sensor disconnected and key ON, probe the signal wire on the harness side. A constant 12V or improper 5V reference confirms a short-to-power in the harness.

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

   Isolate the Fault

   Based on the diagnostic checks above, determine if the fault is the harness or the sensor.

3. 3

   Harness Repair

   Trace the sensor wiring harness back to the main engine harness interface. Look for pinch points or areas where the wire loom has degraded. Cut out the shorted section of the wire, solder in a new section of wire, and seal it with heat-shrink tubing.

4. 4

   Sensor Replacement

   Unplug the electrical connector from the Boost Air Temperature Sensor. Unthread the sensor from the intake manifold/piping using a deep socket or wrench. Install the new sensor. (Do not overtighten, as these are often brass or plastic threads). Reconnect the electrical connector, ensuring the locking tab clicks into place.

5. 5

   Clear Codes and Test

   Reconnect the battery. Turn the key to the ON position and clear the inactive fault codes via the H-Menu on the instrument cluster or using a CNH Electronic Service Tool (EST). Start the engine and verify that the t29 code does not return.