Case IH 158-14 - BCM – BCM: Keyswitch Battery Potential - Inconsistent / Invalid

The control module is receiving an inconsistent, erratic, or invalid voltage signal from the ignition key switch when it is turned, typically caused by worn internal contacts inside the ignition switch, a loose wiring connection, or a failing relay.

• MAGNUM AFS Connect
• Magnum series
• Steiger series
• Puma
• Maxxum
• Farmall models
• Axial-Flow series
• Patriot sprayers
• CPX series pickers

1. 1

   Check the resting battery voltage (should be 12.4V-12.8V) and running voltage (13.5V-14.4V). A weak battery can cause voltage drops during cranking that trigger this code.

2. 2

   Inspect the main battery cables, chassis grounds, and cab ground straps for corrosion or looseness.

3. 3

   Use a multimeter to back-probe the ignition switch connector. Monitor the voltage on the switched power wire (Terminal 15) while wiggling the key in the 'ON' and 'START' positions. Look for erratic voltage drops.

4. 4

   Inspect the wiring harness between the ignition switch and the BCM for chafing. Check the ignition/cab power fuses and relays to ensure they are fully seated and not corroded.

1. 1

   Disconnect Power

   Always disconnect the negative battery cable before working on the BCM or ignition circuits to prevent short circuits.

2. 2

   Access the Switch

   Remove the steering column shrouds or the side dash trim panels to gain access to the rear of the ignition switch.

3. 3

   Disconnect Harness

   Unplug the electrical pigtail/harness connector from the back of the ignition switch.

4. 4

   Remove the Switch

   Unscrew the retaining bezel nut on the front of the dash panel that holds the switch in place. Pull the old switch out from the rear.

5. 5

   Install New Switch

   Insert the new ignition switch through the dash panel, align the anti-rotation notch, and tighten the front retaining nut.

6. 6

   Reconnect

   Plug the electrical harness into the new switch.

7. 7

   Reassemble

   Reinstall the dash panels and steering column shrouds.

8. 8

   Test

   Reconnect the negative battery cable. Turn the key to verify the machine powers up consistently and the 158-14 fault code clears (or changes to an inactive/historic state).