Case IH 81 – ECM / Transmission Control Module: Transmission Hydraulic Oil Pressure Switch Short to Ground or Open (Open Circuit Error)

The system registers this fault when it detects an open circuit or a short to ground in the transmission pressure switch circuit. Specifically, if the pressure switch does not detect a pressure above 11 bar (160 psi) within the first 30 seconds of startup, a signal is not sent to the dump solenoid to engage the clutch packs, and the error is registered.

• JXC
• Farmall series
• JX series
• Maxxum (MXM 120-190)
• Magnum (MX210, MX230, MX255, MX285)
• Steiger series
• TN Series
• TNA Series
• TN60A
• TN70A
• TN75A
• TN85A
• TN95A
• TG245
• T8040

1. 1

   Check for a short to ground or an open circuit between ECM connector 2, pin 20 and the Transmission Pressure Switch

2. 2

   Inspect the signal wiring between the Transmission Pressure Switch and ECM connector 2, pin 31

3. 3

   Test the common 5-volt sensor supply wire coming from the ECM to ensure the switch is receiving proper reference voltage

4. 4

   Inspect the physical terminals on the switch itself for corrosion, backed-out pins, or damage

5. 5

   Verify that the transmission is actually building hydraulic pressure. The system expects to see pressure reach above 11 bar (160 psi) within 30 seconds of startup. If mechanical pressure is not being built, the issue may be a hydraulic pump or internal leak rather than the electrical switch

1. 1

   Safety First

   Park the tractor on a level surface, engage the parking brake, and disconnect the battery before servicing the electrical system.

2. 2

   Locate the Switch

   Locate the transmission pressure switch, typically mounted on the transmission control housing / valve block.

3. 3

   Disconnect Wiring

   Carefully unplug the electrical connector from the pressure switch.

4. 4

   Remove the Faulty Switch

   Using the appropriate wrench, unthread the faulty transmission pressure switch from the housing. Have a shop rag ready, as a small amount of hydraulic fluid may leak.

5. 5

   Install the New Switch

   Thread the new transmission pressure switch into the port. (Note: The standard fitting for this switch is an M12 x 1.5mm thread). Tighten to OEM specifications.

6. 6

   Reconnect Wiring

   Plug the electrical harness back into the new switch, ensuring the locking tab clicks into place.

7. 7

   Test the System

   Reconnect the battery. Start the tractor and monitor the dash/ECM. The transmission oil pressure must reach 11 bar (160 psi) within 30 seconds for the ECM to send the signal to the dump solenoid and allow the clutch packs to engage. Verify that Fault Code 81 clears (Auto Reset).