Case IH t27 – Engine Control Module (ECM): Boost Air Temperature Sensor (PHY), Data Incorrect

The control module is receiving an implausible, erratic, or out-of-range signal from the boost air temperature sensor.

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

1. 1

   Visually inspect the boost air temperature sensor, its electrical connector, and the wiring harness for physical damage, corrosion, or loose pins.

2. 2

   Test the wiring harness for open circuits, shorts to ground, or shorts to a high voltage source (B+).

3. 3

   Disconnect the sensor and measure the resistance across its pins using a multimeter. Compare readings to ambient temperature (e.g., 60°C = 595 ohms, 80°C = 322 ohms, 100°C = 186 ohms, 120°C = 112 ohms).

4. 4

   Turn the key to the ON position (engine off) and probe the harness connector to ensure the ECM is supplying the correct 5V reference voltage to the sensor.

1. 1

   Preparation

   Turn off the engine, remove the key from the ignition, and allow the engine and charge air piping to cool down. Disconnect the negative battery cable.

2. 2

   Locate the Sensor

   Locate the boost air temperature sensor. It is typically mounted on the intake manifold or on the charge air cooler (intercooler) outlet piping.

3. 3

   Disconnect

   Depress the locking tab on the electrical connector and carefully pull it away from the sensor.

4. 4

   Removal

   Depending on the specific engine variant, the sensor will either be threaded directly into the manifold or held in place by a retaining screw (often an M6 hex flange screw). Unbolt or unthread the faulty sensor and pull it out of the port.

5. 5

   Installation

   Clean the mounting port to ensure a proper seal. Insert the new boost air temperature sensor and tighten the retaining screw or thread it to the manufacturer's specified torque.

6. 6

   Reassembly

   Reconnect the electrical harness, ensuring the connector clicks securely into place. Reconnect the negative battery cable.

7. 7

   Clear Codes

   Connect a compatible heavy-duty diagnostic scanner (such as the CNH Electronic Service Tool or a TEXA Off-Highway scanner using the appropriate 9-pin or specific CNH cable) to the machine's diagnostic port. Clear the t27 fault code.

8. 8

   Verification

   Start the engine and monitor the live data for the boost air temperature to ensure it is reading a plausible value and that the fault code does not return.