Case IH P27 – Tractor Electronic Management Unit / PTO Controller or Engine Electronic Control Unit (EECU) / Engine Control Module (ECM): PTO Speed Sensor Open Circuit / Boost Air Temperature Sensor Data Incorrect

The fault code can indicate either an open circuit in the PTO speed sensor (P27) due to a broken wire, unplugged connector, or failed sensor, or an erratic, implausible, or incorrect signal from the Boost Air Temperature Sensor (T27) to the Engine Electronic Control Unit.

• MXM
• Case IH MXM Series
• MXM 120
• MXM 130
• MXM 140
• MXM 155
• MXM 175
• MXM 190
• Magnum Series
• Puma Series
• Farmall Series

1. 1

   If diagnosing T27 (Boost Air Temp): Locate the Boost Air Temperature sensor (often designated as B123) on the intake manifold/aftercooler.

2. 2

   If diagnosing T27 (Boost Air Temp): Inspect the wiring harness and connector for physical damage, corrosion, or loose pins.

3. 3

   If diagnosing T27 (Boost Air Temp): Test the sensor using a multimeter. Because it is an NTC thermistor, its resistance should drop as temperature increases (e.g., 60°C = 595 ohms / 2.170 Volts; 80°C = 322 ohms / 1.480 Volts; 100°C = 186 ohms / 0.982 Volts; 120°C = 112 ohms / 0.643 Volts).

4. 4

   If diagnosing P27 (PTO Speed Sensor): Check if the PTO speed sensor connector (designated as C054) is connected correctly.

5. 5

   If diagnosing P27 (PTO Speed Sensor): Disconnect connector C054.

6. 6

   If diagnosing P27 (PTO Speed Sensor): Using a suitable multimeter, access the speed sensor terminals and check for an open circuit. If an open circuit is indicated across the sensor pins, the sensor has failed.

7. 7

   If diagnosing P27 (PTO Speed Sensor): If the sensor tests good, check the wiring at C054. Check for continuity between C054 (pin RM57R–B) and the chassis ground. If there is no continuity, the ground wiring has failed.

1. 1

   Disconnect battery

   If diagnosing T27: Disconnect the tractor's battery to prevent electrical shorts.

2. 2

   Disconnect wiring harness

   If diagnosing T27: Disconnect the wiring harness from the Boost Air Temperature Sensor.

3. 3

   Remove sensor

   If diagnosing T27: If the multimeter test shows resistance values far outside the OEM specifications (or an open/shorted internal circuit), remove the sensor using a deep socket or wrench.

4. 4

   Install new sensor

   If diagnosing T27: Install the new Boost Air Temperature Sensor and torque to OEM specifications.

5. 5

   Reconnect and clear codes

   If diagnosing T27: Reconnect the wiring harness, reconnect the battery, and clear the fault codes using the tractor's H-Menu or a diagnostic tool.

6. 6

   Ensure tractor is off

   If diagnosing P27: Ensure the tractor is off and the battery is disconnected.

7. 7

   Locate PTO speed sensor

   If diagnosing P27: Locate the PTO speed sensor, which is fitted within the rear PTO housing.

8. 8

   Disconnect socket

   If diagnosing P27: Disconnect the 2-pin socket (C054).

9. 9

   Remove old sensor

   If diagnosing P27: If the sensor failed the continuity test, unthread the old sensor from the PTO housing.

10. 10

    Install new sensor

    If diagnosing P27: Install the new PTO speed sensor.

11. 11

    Repair wiring

    If diagnosing P27: If the sensor was good but the ground test failed, trace the wiring harness from C054 back to the electronic management unit and repair the broken wire/ground connection.

12. 12

    Reconnect and test

    If diagnosing P27: Reconnect the harness, power the tractor, and test PTO engagement.