What Does B1509 Mean?
This code indicates the Body Control Module (BCM) has detected that the flash-to-pass switch circuit is shorted to battery voltage. The flash-to-pass switch allows drivers to briefly activate the high beam headlights by pulling the turn signal stalk. The BCM has identified that the switch circuit is receiving constant battery voltage when it should normally be at ground or open, indicating a wiring fault or switch internal failure.
Common Causes
45%
Damaged or chafed wiring harness causing short to power in the flash-to-pass switch circuit
35%
Failed multifunction switch or turn signal stalk with internal short to battery
15%
Water intrusion or corrosion in steering column connectors causing cross-circuit short
5%
Failed or defective Body Control Module with internal circuit fault
Diagnostic Steps
1
Step 1: Perform visual inspection of the multifunction switch wiring harness along the steering column, checking for pinched, chafed, or damaged wires that may be contacting battery voltage sources. Pay special attention to areas where harness passes through steering column covers.
2
Step 2: Disconnect the multifunction switch connector and use a digital multimeter to measure voltage on the flash-to-pass switch circuit pin at the harness side (BCM side) with ignition on. Reading should be 0 volts; battery voltage confirms short in wiring harness between BCM and switch.
3
Step 3: If no voltage found at harness, check resistance between the flash-to-pass circuit pin and battery positive with switch disconnected and ignition off. Reading should be infinite ohms (open circuit); low resistance confirms short to power in wiring.
4
Step 4: If wiring tests normal, reconnect harness and back-probe the flash-to-pass switch circuit at the connector while cycling the switch. Voltage should pulse only when switch is activated; constant battery voltage indicates internal switch failure.
5
Step 5: Inspect all connectors for corrosion, water intrusion, or pushed-out pins that could create cross-circuit contamination with adjacent power circuits.
6
Step 6: After repair, clear codes, cycle the flash-to-pass switch multiple times, and verify code does not return and high beams flash properly without staying illuminated.
Estimated Repair Cost
$100 - $450
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected that the flash-to-pass switch circuit is shorted to battery voltage. The flash-to-pass switch allows drivers to briefly activate the high beam headlights by pulling the turn signal stalk. The BCM has identified that the switch circuit is...
The most common cause of B1509 (Flash To Pass Switch Circuit Short To Battery) is: Damaged or chafed wiring harness causing short to power in the flash-to-pass switch circuit
Typical repair costs for B1509 range from $100 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to continue driving as this only affects the flash-to-pass feature for signaling other drivers. However, there is potential for high beams to remain stuck on if the short worsens, which could blind oncoming traffic and create a safety hazard, so repair should be completed within a reasonable timeframe.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1509 to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Body
System
Body Control and Lighting System
Difficulty
Type
Manufacturer
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
