U0274: Lost Communication With Lighting Driver Control Module B
What to do
Look at your lights at night, from outside the car, and compare the two sides. This module drives part of the lighting rather than all of it, so the symptom is often not a lamp that is off but one that is dimmer, missing part of its pattern, or no longer changing shape — which is easy to miss from the driving seat.
If you have adaptive or matrix headlights, do not leave this. Losing part of the control can leave sections of the beam lit that should be dipped for oncoming traffic — you would be dazzling other drivers with nothing inside the car to tell you. That is a reason to act promptly even if the road ahead looks fine to you.
If both sides have gone, that is usually one shared fault — a fuse, a supply, or the wiring feeding the front of the car — rather than two modules failing. Cheaper, and worth checking first.
See U0273 for the question worth asking before a lamp assembly is ordered.
What this code means
The second lighting driver control module has stopped being heard from. See U0273 for what a lighting driver is and why the driver-versus-lamp distinction is worth money.
Multiple drivers exist because a modern lighting installation has more independently controlled elements than a single unit can feed. Low beam, high beam, daytime running lights, indicators, position lights and cornering elements may each need their own regulated supply — and on adaptive systems, individual segments of a matrix headlamp are switched separately so the beam can be shaped around other traffic.
That segmentation produces a symptom worth recognising: partial lighting. Not a lamp that is out, but a lamp that is dimmer than its partner, missing part of its pattern, or no longer changing shape as it should. Nothing is completely dark, so nothing looks obviously broken — and a driver may not notice at all.
Standing in front of the vehicle at night and comparing the two sides is the test, exactly as at U0242, and asymmetry is the evidence.
One consequence deserves stating because it affects other people rather than you: a matrix or adaptive system that has lost part of its control may leave segments lit that should be dipped for oncoming traffic. That is dazzling other drivers without any indication inside the car. It is a good reason not to leave this code for weeks even if your own view of the road seems fine.
And the counting logic applies as elsewhere: both drivers silent points at a shared supply or the network branch feeding the front of the vehicle, which is the cheaper and commoner answer, rather than at two failures.
Likely causes
Start here
- Water ingress into module · moderate
- Corroded or loose connector · easy
- Blown fuse or failed supply · easy
- Heat damage to sensor or wiring · moderate
Less common
- Damaged wiring harness · moderate
- Failed power or earth supply to the module · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
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