What Does B0508 Mean?
This code indicates the Body Control Module (BCM) has detected a fault in the left-hand daytime running light (DRL) relay control circuit. The BCM monitors the relay coil circuit for proper voltage and current flow, and has identified an open circuit, short circuit, or excessive resistance condition. This prevents the left DRL relay from operating correctly, affecting the left side daytime running lights.
Common Causes
35%
Failed DRL relay with open or shorted coil windings
30%
Damaged or corroded wiring between BCM and DRL relay, including poor ground connection
20%
Corroded or loose relay socket/connector terminals causing poor contact
15%
Internal BCM fault in relay driver circuit or output stage
Diagnostic Steps
1
Step 1: Locate the left DRL relay in the fuse/relay box and perform visual inspection of relay and socket for corrosion, burning, or physical damage. Remove relay and inspect socket terminals for bent pins or corrosion
2
Step 2: Using a multimeter, test the relay coil resistance between terminals (typically 70-120 ohms for a standard automotive relay). Replace if open circuit or out of specification
3
Step 3: With relay removed and ignition on, check for battery voltage at the power supply terminal of the relay socket using a multimeter. Then check for BCM control signal by measuring voltage at the relay coil control terminal during DRL activation
4
Step 4: If power and control signals are correct, check circuit continuity and resistance from BCM connector to relay socket using wiring diagram for pin identification. Look for open circuits, shorts to ground, or excessive resistance (should be less than 1 ohm)
5
Step 5: Install a known-good relay and clear codes. Cycle the DRL system on/off and monitor for code return. If code returns immediately with good relay and verified wiring, suspect BCM internal fault
6
Step 6: After repairs, verify proper DRL operation on left side and confirm no codes return after multiple drive cycles
Estimated Repair Cost
$75 - $450
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected a fault in the left-hand daytime running light (DRL) relay control circuit. The BCM monitors the relay coil circuit for proper voltage and current flow, and has identified an open circuit, short circuit, or excessive resistance condition...
The most common cause of B0508 (LH DRL Relay Circuit) is: Failed DRL relay with open or shorted coil windings
Typical repair costs for B0508 range from $75 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to continue driving as DRLs are supplementary lighting and not required for vehicle operation in most jurisdictions. However, reduced visibility to other drivers during daytime may slightly increase accident risk, 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 B0508 to identify the root cause.
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Quick Info
Category
Body
System
Exterior Lighting System
Difficulty
Type
Generic (SAE)
Recommended Tools
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