U0183: Lost Communication With Lighting Control Module — Rear A
What to do
Before you drive anywhere, get somebody to stand behind the car while you work through the brake pedal, the indicators, the hazards, the lights, the fog light and reverse gear.
That is not a formality. Every light this fault affects is behind you, so you cannot see any of them. A headlight that fails is obvious the first time it is dark. Brake lights that have stopped working are invisible to you and remove the only warning the driver behind gets. In most places driving without them is also an offence.
Then, if you tow: unplug the trailer or caravan and see whether the fault clears. On most cars the same computer runs the trailer socket and checks its bulbs, so a fault in the trailer, a wrong bulb, or a towing kit spliced into the wiring rather than fitted properly will produce this code with nothing wrong on the car at all. That test is free and settles a lot of these.
Otherwise, look under the boot floor where the spare wheel lives. Standing water there — from an aged tailgate seal, a blocked drain or a hardened rear light gasket — is a very common cause. And if the fault comes and goes, open and close the tailgate slowly and watch, because the wiring runs through the hinge and flexes every time.
If any brake light, indicator or rear light is not working, the car should not be driven until it is fixed.
What this code means
The rear lighting control module has stopped being heard from. The general reasoning is at U0100, module B is at U0252, and U0484 covers the same module reporting implausibly instead.
This code carries a higher severity than the rest of the lighting family for one reason, and it is worth stating without decoration: the driver cannot see any of the lights this module operates.
Brake lights, indicators, tail lights, fog lights and reversing lights are all behind the driver. A headlight that fails announces itself on the first dark road. A brake light that fails announces itself to nobody at all — and a vehicle braking with no brake lights removes the only warning the driver behind gets.
So the first action is to have somebody stand behind the vehicle and go through every function. It takes a minute and it is the whole safety content of this page. In most jurisdictions driving without working brake lights or indicators is also an offence.
Then one free test resolves a large share of these. On most vehicles the rear lighting module also drives the trailer socket and performs its bulb-failure detection. Unplug the trailer, clear the code and see whether it returns — if it does not, the fault is in the trailer or its wiring rather than the vehicle, which is a far cheaper conversation. A towing loom spliced into the harness rather than fitted through the vehicle's proper interface is a leading cause, and it is the same argument as U0137.
After that, the rear of the vehicle's usual list: water reaching the module through an aged tailgate seal or a hardened light cluster gasket — lift the boot floor and look under the spare wheel — connectors behind the rear trim disturbed for boot liners and audio work, and the harness through the tailgate hinge, which flexes like a door boot and fails the same way.
And the same expensive note as U0182 applies: rear clusters are increasingly sealed LED assemblies, so establish whether the fault is the module, the wiring or the lamp before an assembly is ordered.
Likely causes
Start here
- Poor wiring splice in an aftermarket installation · moderate
- Water ingress into module · moderate
- Corroded or loose connector · easy
- Broken wire in the door harness boot · moderate
Less common
- Blown fuse or failed supply · easy
- Damaged data bus wiring · 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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