B1568

What Does Code B1568 Mean?

Diagnostic Trouble Code B1568 signifies that the vehicle’s Body Control Module (BCM), or in some architectures, the Front Electronic Module (FEM) or Central Gateway Module (CGW), has detected an open circuit condition within the high-beam headlamp circuit. This means that the control module, upon commanding the high-beam headlamps to illuminate, does not detect the expected electrical current flow or voltage drop through the circuit, indicating a complete interruption in the electrical path. Essentially, the module interprets this as a break in the wiring, a faulty bulb filament, or another component preventing electricity from reaching the high-beam lamp, rendering it inoperative. The BCM actively monitors the circuit’s resistance and current draw; an “open” state implies infinite resistance, preventing the lamp from functioning.

Common Symptoms

• High-beam headlamps fail to illuminate when activated by the driver.
• The high-beam indicator lamp on the instrument cluster does not illuminate or may flicker intermittently.
• A “Check Headlamps” or similar warning message may appear on the instrument cluster display.
• Reduced forward visibility during nighttime driving conditions, particularly on unlit roads.

What Causes the Code B1568?

• Blown High-Beam Headlamp Bulb(s): The most prevalent cause, as an open filament within the bulb creates an open circuit.
• Corroded or Loose Electrical Connections: Poor contact at the headlamp connector, inline harness connectors, or module connectors.
• Damaged or Severed Wiring: An open circuit in the power supply or ground wire for the high-beam headlamp due to chafing, impact, or rodent damage.
• Faulty Headlamp Relay: If the high-beam circuit utilizes a dedicated relay, an internal fault or failure of the relay can cause an open circuit.
• Compromised Ground Connection: A corroded or loose ground wire or ground point for the headlamp circuit.
• Faulty Headlamp Switch/Multi-Function Switch: An internal open within the switch preventing the high-beam command signal or power flow.
• Internal Control Module Fault (Less Common): A rare internal malfunction within the BCM, FEM, or other lighting control module.

How to Diagnose and Troubleshoot

A systematic diagnostic approach is essential to accurately pinpoint the cause of B1568:

1. Visual Inspection:
   • Begin by visually inspecting the high-beam headlamp bulbs for any visible signs of a broken filament or discoloration.
   • Carefully examine the entire wiring harness leading to the high-beam headlamp assembly. Look for any signs of physical damage, chafing, pinching, or corrosion on wires and connectors. Pay particular attention to the headlamp connector itself and any chassis ground points.
2. Bulb Functionality Test:
   • If only one high-beam is affected, swap the suspected faulty bulb with a known good bulb (e.g., from the opposing side if functional, or a new replacement). If the problem resolves, the bulb was the issue.
3. Voltage Measurement (DMM Required):
   • With the ignition ON and high beams commanded ON, use a Digital Multimeter (DMM) to measure the voltage at the high-beam headlamp connector. Place the positive lead on the power wire for the high-beam and the negative lead on a known good chassis ground. Expect to see near battery voltage (typically 12.0-14.5V).
   • If no voltage is present, trace the power wire backward towards the fuse box, relay, or BCM, checking for voltage at each major junction to identify where power is lost.
   • Next, check the ground circuit. With the high beams ON, place the positive lead of the DMM on the positive terminal of the battery and the negative lead on the ground wire at the headlamp connector. A reading near battery voltage indicates a good ground. A reading of 0V or very low voltage suggests an open or high-resistance ground path.
4. Continuity Test (DMM Required):
   • Disconnect the vehicle’s battery.
   • Isolate the relevant high-beam circuit by disconnecting connectors at both the headlamp assembly and the BCM (or corresponding control module).
   • Using the DMM in continuity or resistance mode, measure the resistance of the power and ground wires of the high-beam circuit between the module and the headlamp connector. A healthy wire should exhibit very low resistance (typically less than 0.5 ohms). An “OL” (Open Loop) reading or significantly high resistance confirms a break in the wire.
5. Fuse and Relay Inspection:
   • Locate the fuse(s) for the high-beam headlamps in the vehicle’s fuse box(es). Visually inspect them for breakage or use the DMM in continuity mode to test across the fuse terminals. Replace any blown fuse.
   • If a high-beam relay is present, swap it with a known good relay from a non-critical, identical circuit, or test its functionality using a relay tester or by manually actuating it with external power and checking for continuity across its switched terminals.
6. Advanced Scanner Diagnostics:
   • Utilize an advanced diagnostic scanner capable of accessing BCM/lighting module live data. Monitor PIDs (Parameter IDs) such as “high beam switch status” and “high beam output command” to verify if the BCM is correctly receiving the driver’s command and attempting to energize the circuit.

Recommended Repairs and Solutions

Once the root cause has been identified through proper diagnosis, implement the following repairs:

• Replace Blown Headlamp Bulb(s): This is the most common resolution. Always use bulbs of the correct type, wattage, and voltage specified by the manufacturer. Consider replacing bulbs in pairs to ensure symmetrical light output and lifespan.
• Repair or Replace Damaged Wiring/Connectors: If an open circuit is found in the wiring, perform a professional repair using appropriate automotive-grade wire, waterproof heat-shrink tubing, and secure crimp connectors or solder joints. For corroded connectors, clean the terminals thoroughly or replace the entire connector assembly if corrosion is severe. Ensure all ground points are clean, tight, and free of corrosion.
• Replace Blown Fuse: If a blown fuse is found, replace it with a new fuse of the exact specified amperage rating. Investigate if there was an underlying short circuit that caused the fuse to blow to prevent recurrence.
• Replace Faulty Relay: If the high-beam relay tests faulty, replace it with a new OEM-equivalent relay.
• Address Ground Issues: Clean and re-secure any corroded or loose ground connections related to the headlamp circuit. Ensure a low-resistance path to chassis ground.
• Replace Faulty Switch: If the headlamp switch or multi-function stalk switch is determined to be the cause of the open circuit, replace it with an OEM or high-quality aftermarket equivalent.
• Control Module Replacement (Last Resort): Only consider replacing the BCM or lighting control module if all other potential causes have been thoroughly ruled out, and diagnostic testing indicates an internal module failure. This often requires professional programming or coding after installation.
• Post-Repair Verification: After completing any repair, clear the DTC B1568 from the vehicle’s memory using an OBD-II scanner. Test the high-beam headlamp functionality multiple times to confirm the repair, and then perform a road test to ensure the code does not return and the system operates correctly under various conditions.