U0181: Lost Communication With Headlamp Leveling Control Module A
What to do
Check what your headlights are actually doing before driving at night, because this fails in two opposite ways.
If the beam suddenly does not reach anywhere — a pool of light a few metres in front of the car on an unlit road — that is the levelling system parked at its lowest position. It is the safe failure, and it is still genuinely dangerous on a dark road at speed. Avoid unlit roads at night until it is fixed.
If oncoming drivers have started flashing you on dipped beam, take it seriously rather than as rudeness. The beam may have been left aimed high, and you cannot see that from the driver's seat — only the people coming towards you can.
Expect two other things to have gone with it. On many cars this module also runs the cornering lights (the extra light that comes on when you turn at low speed) and the automatic main beam dip. If your car has been dipping automatically for oncoming traffic, assume it no longer does and use the stalk.
Ask for the ride height sensor to be checked first. It hangs under the car on a thin plastic link in the road salt, and it breaks. It is cheap, and it is a far commoner cause than the module.
Two things to mention if they apply: if the car has been lowered or re-sprung, the levelling needs recalibrating; and if LED or HID bulbs have been fitted into headlights built for halogen, that causes dazzle no levelling system can fix.
What this code means
The headlamp levelling module has stopped being heard from. The general reasoning is at U0100, and U0482 explains why self-levelling is a legal requirement on gas discharge and LED headlamps rather than a convenience — at those light outputs a few degrees is the difference between illuminating the road and blinding somebody.
Silence normally parks the actuators at their rest position, and on most systems that is the lowest. So the common complaint is the one from U0482: "my headlights suddenly do not reach anywhere" — a pool of light a few metres ahead on an unlit road, which is genuinely dangerous at speed and is rarely connected to a stored code.
The opposite case is the one the driver never sees. Where the actuators have stopped part-way or at the top of their travel, the beam is left high and only oncoming traffic knows. Being flashed repeatedly on dipped beam is information rather than rudeness.
Two things go quiet with it on many vehicles, and they are worth expecting rather than reporting separately. This module frequently also drives the static cornering lamps — the extra light that comes on at low speed on the side you are turning toward — and the automatic main beam dip. If the vehicle has been dipping automatically for oncoming traffic, assume it no longer does, and use the switch.
Where the fault usually is, and it is cheap: the ride height sensor and its link, hanging under the vehicle on a suspension arm in the salt, with a thin drop link and a small plastic ball joint that perishes. Far likelier than the module, and the first thing to ask for.
Two cases get blamed on this code and are not it. A lowered or re-sprung vehicle needs the levelling calibrated to its new ride height. And an LED or HID bulb in a housing built for halogen dazzles in a way no levelling system can correct, because the beam pattern is wrong rather than the aim.
Likely causes
Start here
- Ride height sensor out of adjustment · moderate
- Corroded or loose connector · easy
- Damaged wiring harness · moderate
- Blown fuse or failed supply · easy
Less common
- Water ingress into connector · moderate
- Damaged data bus wiring · moderate
Symptoms
Components involved
Information, not instruction
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Community experience
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