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DTC codes / B08xx · Airbags, seats, doors, lights and comfort systems / B0810

B0810Left Headlamp Low Beam Circuit

This code indicates that the body control module (BCM) or lighting control module has detected an abnormal condition in the left headlamp low beam circuit, such as an open circuit, short to ground, or short to power. The module monitors the current or voltage on the control circuit and sets the code when the expected electrical load is not present or is out of range.

SystemBody
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaAirbags, seats, doors, lights and comfort systems

Symptoms you may notice

  • The left low beam headlamp does not illuminate when the headlights are switched on.
  • The right low beam may still work normally, but some vehicles default to a fail-safe mode that disables both low beams.
  • A warning light or message on the dashboard indicating a lighting system fault.
  • Intermittent operation of the left low beam, often flickering or turning off over bumps.
  • Often no symptoms besides the warning light if the bulb is still functional but the circuit resistance is slightly out of specification.

Common causes, most likely first

  1. Failed low beam bulb or corroded bulb socket contacts.
  2. Damaged wiring harness between the BCM and the headlamp assembly, often from chafing or rodent damage.
  3. Blown fuse or failed relay dedicated to the left low beam circuit.
  4. Faulty headlamp switch or multifunction switch not sending the correct input to the BCM.
  5. Internal failure in the BCM or lighting control module driver circuit.
  6. Poor ground connection at the left headlamp or chassis ground point.
  7. Aftermarket LED or HID bulb installation causing incorrect current draw.

How to diagnose and fix it

  1. Verify the left low beam bulb is good by swapping it with the right side or testing with a multimeter.
  2. Inspect the bulb socket and connector for corrosion, melting, or loose terminals.
  3. Check the fuse and relay for the left low beam circuit, replacing any blown fuse or faulty relay.
  4. Disconnect the BCM connector and check for battery voltage and ground on the left low beam control circuit with the headlights commanded on.
  5. Perform a voltage drop test on the ground circuit and repair any excessive resistance.
  6. Inspect the wiring harness for damage, especially near the headlamp assembly and along the fender.
  7. If all external circuits test good, test the BCM output with a scan tool and bidirectional control; replace the BCM only after confirming it cannot drive the circuit.

What the BCM sees before it sets B0810

  • The BCM often sets this code based on current draw, so a bulb that still lights but draws slightly wrong current can trigger it without any visible failure.
  • Aftermarket LED bulbs frequently cause this code because their low current draw falls outside the module's expected range, even though they appear to work.
  • A shorted bulb can damage the BCM driver, so always replace the bulb before installing a new or rebuilt module to avoid repeat failure.
  • The left and right low beam circuits may share a common ground or power feed, so a fault on the opposite side can sometimes affect both circuits.
  • Some vehicles require a relearn or reset procedure after bulb replacement to clear the code and restore normal operation.

Can I keep driving with B0810?

You can usually drive safely during daylight, but avoid driving at night or in low-visibility conditions until the fault is repaired because the left low beam may be inoperative. If both low beams are out, do not drive after dark.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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