Case IH 3951-14 - BCM – BCM: Tractor horn switch - invalid input voltage

The Body Control Module detects a voltage reading from the horn switch circuit that falls outside the expected parameters. This typically indicates a short to ground, a short to power, an open circuit in the horn switch wiring, or an internal failure of the horn switch itself.

• MAGNUM AFS Connect
• Magnum 380 AFS Connect
• Magnum 400 AFS Connect

1. 1

   Visual Inspection: Inspect the wiring harness and connectors between the horn switch (located on the steering column or multifunction handle) and the BCM for pinched wires, chafing, corrosion, or loose pins.

2. 2

   Switch Continuity Test: Disconnect the horn switch. Using a multimeter, measure the resistance across the switch terminals. It should read less than 1 ohm when the switch is pressed, and show an open circuit (infinite resistance) when released.

3. 3

   Circuit Ground Test: Check the switched ground circuit from the horn switch to the BCM. If the resistance is high, there is an open in the switched ground circuit.

4. 4

   Voltage Check: With the key ON, check for the correct reference voltage at the horn switch connector to ensure the BCM is supplying power to the circuit.

5. 5

   Bypass Test: If the wiring tests good, temporarily jump the switch connector pins. If the horn sounds and the BCM registers the input, the switch is definitively the point of failure.

1. 1

   Disconnect Power

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

2. 2

   Access the Switch

   Remove the retaining screws on the steering column shroud or the multifunction armrest panel (depending on your exact cab configuration) to expose the rear of the horn switch.

3. 3

   Disconnect the Harness

   Unplug the electrical connector from the back of the horn switch.

4. 4

   Remove the Switch

   Depress the retaining tabs or remove the mounting screws holding the switch in place, and pull the faulty switch out of the console/column.

5. 5

   Install the New Part

   Push the new horn switch into the mounting slot until it clicks into place or secure it with the retaining screws.

6. 6

   Reconnect

   Plug the electrical harness back into the switch.

7. 7

   Reassemble

   Reinstall the steering column shrouds or armrest panels.

8. 8

   Test

   Reconnect the battery, turn the ignition ON, and press the horn to verify operation. Clear the inactive 3951-14 code from the BCM using your diagnostic tool.