Case IH t26 – Engine Control Unit (ECU): Boost Air Temperature Sensor (PHY), Grounded Or Current Above Normal Range

The control module is receiving a voltage signal from the boost air temperature sensor that is too high or indicates a direct short to ground in the sensor circuit.

• MXM
• MXM Series
• MXM 120
• MXM 130
• MXM 140
• MXM 155
• MXM 175
• MXM 190
• Maxxum
• Puma
• Magnum
• Steiger

1. 1

   Visually inspect the boost air temperature sensor on the intake manifold and its wiring harness for chafing, melted insulation, or exposed wires shorting to the engine block.

2. 2

   Disconnect the sensor and inspect the connector pins for corrosion, moisture, or pushed-out terminals.

3. 3

   Test the sensor's signal wire with a multimeter for continuity to ground. If the wire is grounded while disconnected from the sensor, the wiring harness is at fault.

4. 4

   Verify proper 5V reference and ground are present at the connector without shorts. If the wiring tests fine, the internal thermistor of the sensor has likely failed.

1. 1

   Preparation

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

2. 2

   Removal

   Locate the Boost Air Temperature Sensor on the intake manifold. Press the release tab on the electrical connector and pull it off the sensor.

3. 3

   Extraction

   Using the appropriate socket or wrench, carefully unthread the faulty sensor from the intake manifold.

4. 4

   Installation

   Thread the new sensor into the manifold by hand to prevent cross-threading, then tighten it to the OEM torque specification.

5. 5

   Reconnection

   Plug the electrical connector back into the new sensor, ensuring it clicks securely into place.

6. 6

   Clearing Codes

   Reconnect the battery. Turn the key to the ON position and use the tractor's H-Menu (or a connected diagnostic tool) to clear the stored t26 fault code. Start the engine and verify the code does not return.