Case IH 4026-03 - BCM – BCM: Right mirror heater - short circuit to B+

The system has detected a "short circuit to B+" on the right mirror's heating circuit. This means the circuit is improperly receiving continuous battery voltage, the ground side is shorted to a power source, or the heating element inside the mirror glass has failed internally and shorted to the power feed.

• MAGNUM AFS Connect
• Magnum 250 AFS Connect
• Magnum 340 AFS Connect
• Magnum 380 AFS Connect
• Magnum 400 AFS Connect
• Optum AFS Connect
• Steiger AFS Connect

1. 1

   Inspect the wiring harness running from the right cab A-pillar to the right mirror arm for pinched wires, chafing, or damaged insulation at the mirror arm hinge.

2. 2

   Disconnect the electrical connector at the right mirror assembly, turn the key on, and activate the mirror heater switch.

3. 3

   Use a multimeter to check for voltage on the ground circuit. If voltage is present, the wiring harness is shorted to power somewhere between the BCM and the mirror.

4. 4

   Measure the resistance across the heater element pins on the mirror glass. If the multimeter reads 0 ohms, the heating element inside the glass is internally shorted.

5. 5

   Verify that the BCM is outputting the correct voltage when the heater switch is engaged and that the switch itself is not stuck or internally shorted.

1. 1

   Disconnect Power

   Disconnect the tractor's battery to prevent further electrical damage or accidental shorts during repair.

2. 2

   Access the Harness

   If the diagnostic checks point to a wiring issue, open the right-hand cab pillar trim to access the BCM harness leading to the mirror.

3. 3

   Repair Wiring

   Repair any chafed or shorted wires using proper automotive-grade heat-shrink connectors.

4. 4

   Replace Mirror Glass/Assembly

   If the short is internal to the mirror heater element, carefully pry the old mirror glass out of the housing (or unbolt the entire mirror assembly if the housing/motor is also damaged). Plug the electrical connectors into the new heated mirror glass and snap it into the housing.

5. 5

   Reassemble and Clear Codes

   Reconnect the battery. Turn on the tractor and use the AFS Pro 1200 monitor (or a dealer diagnostic tool) to clear the archived 4026-03 fault code from the BCM. Test the mirror heater to ensure the code does not return.