Case IH P37 – Instrument Cluster / Rear PTO Controller (XCM) or Engine Control Unit (EDC / PCU): Rear PTO cab switch momentary contact stuck closed (longer than 30 seconds) / Boost Air Pressure Sensor (PHY), Shorted To High Source

Fault Code P37 indicates the rear PTO cab switch momentary contact is stuck closed for longer than 30 seconds. Fault Code T37 indicates the Engine Control Unit is receiving an abnormally high voltage signal from the Boost Air Pressure Sensor, meaning the signal wire is short-circuited to a high voltage source or the sensor failed internally.

• MXM
• MXM Series (MXM 120, 130, 140, 155, 175, 190)
• Puma
• Maxxum
• Magnum

1. 1

   (PTO Switch Cause) Inspect the yellow PTO knob/switch in the cab. Is it physically jammed, sticky from dirt/spills, or failing to spring back into its neutral position?

2. 2

   (PTO Switch Cause) Pop the switch out of the side console and disconnect it. Use a multimeter on the continuity setting across the switch terminals. If it reads continuous (closed) without you pressing it, the internal spring/contacts have collapsed.

3. 3

   (Boost Sensor Cause) Locate the boost air pressure sensor (typically mounted on the intake manifold or suction pipe). Check the wiring harness leading to it for chafing, melted insulation, or pinch points where it might be shorting to another wire.

4. 4

   (Boost Sensor Cause) Unplug the sensor. Look for water ingress, corrosion, or bent pins inside the connector.

5. 5

   (Boost Sensor Cause) With the key ON and the sensor unplugged, use a multimeter to check the harness side. You should have a 5V reference, a ground, and a signal wire. If the signal wire is showing 5V or 12V while unplugged, the wiring harness has a short circuit. If the wiring tests fine, the sensor itself is internally shorted.

1. 1

   Replace PTO switch

   (PTO Switch Cause) Replace the faulty PTO cab switch with a new OEM unit.

2. 2

   Test PTO engagement

   (PTO Switch Cause) Plug it into the harness, snap it back into the console, and test the PTO engagement.

3. 3

   Disconnect battery

   (Boost Sensor Cause) Turn off the tractor and disconnect the negative battery terminal.

4. 4

   Repair wiring harness

   (Boost Sensor Cause) If the wiring harness is damaged, splice and repair the affected wires using heat-shrink connectors, or replace the damaged harness section.

5. 5

   Remove old sensor

   (Boost Sensor Cause) If the harness is good, remove the retaining bolt(s) holding the Boost Air Pressure Sensor to the intake manifold and pull the old sensor out (be careful not to drop debris into the intake).

6. 6

   Install new sensor

   (Boost Sensor Cause) Lubricate the O-ring on the new sensor with a small amount of clean engine oil and press it into the manifold.

7. 7

   Secure sensor

   (Boost Sensor Cause) Secure the retaining bolt and plug in the electrical connector.

8. 8

   Clear error codes

   (Boost Sensor Cause) Reconnect the battery. Access the tractor's 'Fault Archive' via the instrument cluster display (H-Menu) or a diagnostic tool to clear the stored error codes.