Case IH 3965 – Engine ECU (ISM-DI / Perkins ISM-DI DOC): Engine Stop Switch Stuck Closed

The engine stop switch is continuously completing the circuit (stuck closed), which signals the engine to shut down or prevents it from starting.

• skid steer
• SR175
• SV series
• TR series
• L180
• L216
• L220
• L228
• CX42D
• E38D
• Steiger
• Farmall

1. 1

   Visual Inspection: Check the physical engine stop switch in the cab or control panel to ensure it is not mechanically jammed, packed with debris, or physically broken in the depressed position.

2. 2

   Continuity Test: Turn the key switch OFF, disconnect the switch harness, and test for continuity. It should be open in Run and closed in Stop. If closed in both, the switch has failed.

3. 3

   Wiring Harness Test: If the switch tests good, check the wiring harness between the switch and the Engine ECU for a short to ground or a short to a high source.

4. 4

   ECU Verification: If the switch and wiring harness test perfectly, verify the Engine ECU is not malfunctioning and misinterpreting the signal.

1. 1

   Power Down

   Turn off the machine and disconnect the negative battery cable to prevent electrical shorts during repair.

2. 2

   Access the Switch

   Locate the engine stop switch on the operator console or armrest. Remove the retaining bezel or console panel to access the rear of the switch.

3. 3

   Disconnect

   Unplug the electrical connector from the back of the switch.

4. 4

   Replace or Repair

   If the switch failed the diagnostic test: Pop the old switch out of its mounting hole and snap the new OEM replacement switch into place. If the wiring harness failed: Locate the shorted section of the wire. Splice and solder a new section of wire, sealing it with heat-shrink tubing, or replace the affected harness section.

5. 5

   Reconnect

   Plug the electrical connector back into the switch and reassemble the console panel.

6. 6

   Test

   Reconnect the battery. Turn the key to the ON position. Use a diagnostic service tool (or the machine's auxiliary override button) to clear the inactive fault code. Start the engine and test the stop switch to ensure it shuts the engine down properly without throwing the code again.