B1508: Flash-to-Pass Switch Circuit Open
The B1508 code indicates that the vehicle's control module, typically the Front Electronic Module (FEM) in Ford vehicles, has detected an open circuit in the flash-to-pass switch circuit. This switch, usually located on the turn signal stalk or steering column, allows the driver to momentarily activate the high beams by pulling the stalk backward. An open circuit means there is a break in electrical continuity between the switch and the control module, preventing the activation signal from being received. The FEM monitors the circuit and sets this code when it does not detect the expected resistance or voltage from the switch loop.
1. Commonly Affected Makes
2. Most Common Causes
- Faulty or worn flash-to-pass switch
- Open or corroded wiring between the switch and the FEM
- Loose, corroded, or damaged connector pins at the switch
- Internal failure of the Front Electronic Module (FEM)
- Blown fuse for the switch control circuit
- Poor ground connection in the switch circuit
3. Symptoms You Will Notice
- Flash-to-pass function does not work
- High beams may not activate when pulling the stalk
- Check engine or service light may illuminate
4. Step-by-Step Diagnosis
Scan for codes and verify B1508 is present
Inspect the flash-to-pass switch and its connector for damage or corrosion
Check continuity and resistance in the switch circuit wiring between the switch and FEM
Test the switch operation with a multimeter
Check the fuse for the switch circuit
If all else is okay, test the FEM or replace it if necessary
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, it is generally safe to drive with code B1508. The only symptom is that the flash-to-pass feature may not work, but normal high beam operation via the headlight switch should still function. However, it's recommended to have it repaired for convenience and safety.
How much does it cost to fix?▼
The cost to fix B1508 typically ranges from $50 to $200 for a switch replacement, up to $500 or more if the FEM module needs replacement. Diagnostic fees may add $100-$150.