What Does B2504 Mean?
This code indicates that the Body Control Module (BCM) has detected a short to battery voltage in the right front (RF) low beam headlamp circuit. This means the low beam circuit is receiving constant battery voltage when it should not be, typically due to damaged wiring, a failed connection, or internal component failure. The BCM monitors this circuit and sets the code when it detects voltage present on the control side when the headlamp should be off.
Common Causes
45%
Damaged or chafed wiring harness causing the low beam circuit wire to contact a power wire or positive terminal
30%
Failed headlamp bulb socket with internal short to power terminal or corroded/melted socket creating cross-circuit connection
15%
Defective headlamp assembly with internal short circuit between power feed and low beam control wire
10%
Failed Body Control Module with internal relay or driver circuit stuck closed providing constant voltage
Diagnostic Steps
1
Step 1: Perform visual inspection of the right front headlamp assembly, wiring harness, and connectors for obvious damage, melting, chafing, water intrusion, or corrosion. Pay special attention to areas where harness routing passes near sharp edges or moving components.
2
Step 2: Disconnect the right front headlamp connector at the lamp assembly. Using a digital multimeter set to DC voltage, measure voltage at the low beam control wire terminal in the vehicle-side connector with headlamps commanded off. Reading should be 0 volts; battery voltage indicates wiring harness short to power upstream of connector.
3
Step 3: If voltage is present at vehicle-side connector with lamp disconnected, disconnect the BCM connector controlling the headlamp circuit. Measure resistance between the low beam control wire and all power distribution wires in the harness using an ohmmeter. Reading below 10,000 ohms indicates a short circuit in the wiring harness between BCM and headlamp.
4
Step 4: If no voltage found at vehicle-side connector with lamp disconnected, inspect headlamp assembly internal wiring and socket for short circuit. Measure resistance between low beam power feed terminal and low beam control terminal at lamp-side connector; should read open circuit (infinite resistance).
5
Step 5: Repair or replace damaged wiring harness, connector, or headlamp assembly as identified. Clear codes and verify proper headlamp operation in both on and off states, confirming no voltage present on control circuit when headlamps are commanded off.
Estimated Repair Cost
$100 - $600
Parts + labor, varies by vehicle and location
This code indicates that the Body Control Module (BCM) has detected a short to battery voltage in the right front (RF) low beam headlamp circuit. This means the low beam circuit is receiving constant battery voltage when it should not be, typically due to damaged wiring, a failed connection, or inte...
The most common cause of B2504 (RF LAMP LOW BEAM CIRCUIT Short to Battery) is: Damaged or chafed wiring harness causing the low beam circuit wire to contact a power wire or positive terminal
Typical repair costs for B2504 range from $100 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is safe to drive during daylight hours, but the affected low beam may remain constantly on draining the battery or may not function when needed at night, reducing visibility and safety. Repair should be completed promptly to ensure proper nighttime illumination and prevent potential battery drain or electrical fire risk from sustained short circuit.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B2504 to identify the root cause.
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Quick Info
Category
Body
System
Exterior Lighting System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
