B2506: Left High Beam Short to Battery
Diagnostic trouble code B2506 indicates a short to battery positive (B+) in the left high beam circuit. This code is specific to Ford vehicles, where the lighting control module (GEM or BCM) monitors circuit integrity via current and voltage sensing. The module detects abnormally high voltage on the left high beam control circuit when it should be off or pulse-width modulated, signaling a short to B+.
1. Commonly Affected Makes
2. Most Common Causes
- Wiring in the left headlamp circuit (C209/C269) shorted to B+
- Internal high beam relay in the GEM/BCM module shorted (welded contacts)
- Corroded or bridged pins in left headlamp connectors C1005/C1006
- Left headlamp bulb with internal filament short circuit
- Aftermarket electrical modifications (alarms, auxiliary lights) interfering with the circuit
- Damaged output driver in the GEM/BCM module due to overcurrent
3. Symptoms You Will Notice
- Left high beam stays on continuously or operates erratically
- Check engine or service light may illuminate
- Possible blown fuse for the high beam circuit
4. Step-by-Step Diagnosis
Inspect left headlamp connectors C1005/C1006 for corrosion, bent pins, or bridging
Check for aftermarket wiring tapped into the high beam circuit
Disconnect left headlamp and measure voltage at the high beam control wire; if voltage is present with high beams off, trace short to B+
Test the GEM/BCM by swapping with a known-good module if wiring checks out
5. Frequently Asked Questions
Is it safe to drive?▼
Driving is possible but not recommended at night, as the left high beam may stay on and blind oncoming traffic, or fail to operate. The issue is moderate severity and should be repaired soon.
How much does it cost to fix?▼
Repair costs typically range from $100 to $400, depending on whether the cause is a simple wiring repair or a GEM/BCM module replacement.