What Does B2506 Mean?
B2506 indicates the Body Control Module (BCM) has detected an abnormal voltage condition in the left front high beam headlamp circuit, specifically a short to battery voltage. This means the circuit is receiving constant battery power when it should not be, bypassing normal control by the BCM. The fault prevents proper on/off control of the left front high beam and may cause the bulb to remain constantly illuminated or trigger protective circuit shutdown.
Common Causes
45%
Damaged or chafed wiring harness causing the high beam circuit wire to contact battery voltage wire or positive terminal
25%
Failed headlamp bulb socket with internal short circuit creating path to battery voltage
20%
Faulty headlamp assembly with internal short circuit in wiring or sealed beam unit
10%
Defective BCM output driver or internal relay stuck closed providing constant power
Diagnostic Steps
1
Step 1: Perform visual inspection of left front headlamp assembly, bulb socket, and wiring harness from headlamp to BCM. Look for melted insulation, burnt connectors, water intrusion, or obvious wire damage. Check for aftermarket wiring modifications.
2
Step 2: Disconnect the left front high beam bulb connector at the headlamp. Using a digital multimeter, measure voltage at the vehicle-side connector with ignition on and high beams commanded off. Should read 0V; if battery voltage is present, the short is in the vehicle harness between BCM and connector.
3
Step 3: If no voltage present at disconnected connector, reconnect and remove the high beam bulb. Inspect bulb base and socket terminals for signs of melting, corrosion, or crossed terminals. Test socket resistance to ground and battery voltage with multimeter to identify internal socket short.
4
Step 4: If harness shows battery voltage with connector disconnected, isolate the short by disconnecting BCM connector for the lighting circuit. Measure voltage again at headlamp connector. If voltage disappears, BCM has internal fault; if voltage remains, harness has short to power between connectors requiring segment testing.
5
Step 5: After identifying and repairing the fault (replace damaged harness section, socket, or headlamp assembly), clear the DTC code and perform functional test cycling high beams on/off multiple times while monitoring for code return and proper operation.
Estimated Repair Cost
$75 - $600
Parts + labor, varies by vehicle and location
B2506 indicates the Body Control Module (BCM) has detected an abnormal voltage condition in the left front high beam headlamp circuit, specifically a short to battery voltage. This means the circuit is receiving constant battery power when it should not be, bypassing normal control by the BCM. The f...
The most common cause of B2506 (LF LAMP HIGH BEAM CIRCUIT Short to Battery) is: Damaged or chafed wiring harness causing the high beam circuit wire to contact battery voltage wire or positive terminal
Typical repair costs for B2506 range from $75 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, but nighttime driving safety is compromised due to inoperative or improperly functioning high beam on the driver's side reducing visibility. Repair within a few days to maintain full lighting functionality and avoid potential traffic violations.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B2506 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
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