What Does B0502 Mean?
This code indicates the Body Control Module (BCM) has detected a malfunction in the right-hand Daytime Running Light (DRL) relay control circuit. The BCM monitors the relay coil circuit for proper voltage, current draw, and resistance, and has identified either an open circuit, short to ground, short to power, or failed relay. This affects the vehicle's daytime running light system on the right side, preventing proper illumination during daytime operation.
Common Causes
35%
Failed DRL relay with internal coil or contact failure
30%
Damaged or corroded wiring between BCM and DRL relay, including connector issues
20%
Blown fuse or fusible link in DRL relay control circuit
15%
Internal BCM failure in relay driver circuit
Diagnostic Steps
1
Step 1: Locate the right DRL relay in the fuse/relay box and perform visual inspection for physical damage, corrosion, or burnt contacts. Check associated fuse for continuity using multimeter.
2
Step 2: With ignition off, remove the DRL relay and measure coil resistance across relay terminals (typically pins 85 and 86) - should read 70-120 ohms. Test relay operation by applying 12V to coil and verifying contact closure with multimeter continuity test.
3
Step 3: With relay removed and ignition on, backprobe the relay socket control terminal and measure voltage from BCM - should see 12V when BCM commands relay on, 0V when off. If voltage is stuck at 12V or 0V, inspect wiring harness for shorts or opens.
4
Step 4: Check ground circuit at relay socket using multimeter - should read less than 0.5 ohms to chassis ground. Inspect all connectors in circuit for corrosion, bent pins, or moisture intrusion.
5
Step 5: If all relay, wiring, and power/ground circuits test good, suspect BCM internal relay driver failure. Verify BCM connector pins for corrosion and proper seating before condemning BCM.
6
Step 6: After repair, clear codes, command DRL operation using scan tool bidirectional controls if available, and verify proper right DRL illumination and no code return.
Estimated Repair Cost
$75 - $450
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected a malfunction in the right-hand Daytime Running Light (DRL) relay control circuit. The BCM monitors the relay coil circuit for proper voltage, current draw, and resistance, and has identified either an open circuit, short to ground, shor...
The most common cause of B0502 (RH DRL Relay Circuit) is: Failed DRL relay with internal coil or contact failure
Typical repair costs for B0502 range from $75 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive but repair should be scheduled soon, as daytime running lights enhance vehicle visibility to other drivers and may be legally required in some jurisdictions. Primary headlights remain functional for nighttime driving.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B0502 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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