OBD-II code U0484 indicates that a control module on the vehicle (typically the Body Control Module or PCM) is receiving data from the Rear Lighting Control Module that is implausible, incomplete, or corrupted. The fault is set when the received message fails the network's validity checks over the CAN bus or similar communication network. It is a communication/network code, not a direct failure of the rear lights themselves.
Corrosion, loose pins, broken wires, or water intrusion at the rear lighting module connector are the most common cause, since the rear of the vehicle is exposed to moisture, road salt, and wiring harness flexing.
The module itself can fail internally, producing corrupted or out-of-range data on the network. This is a common repair and should be tested before replacement.
A blown fuse, broken ground strap, or high-resistance power supply can cause the module to transmit invalid data as it powers up or operates in a degraded state.
Abnormal resistance on the network backbone, a short between CAN wires, or a damaged termination resistor can corrupt messages from multiple modules, with U0484 being one of the reported faults.
A known software bug or incomplete reflash can cause the module to output non-conformant data until reprogrammed with the latest calibration.
The module that flags U0484 is rarely the cause, but a BCM or gateway internal failure can occasionally misinterpret otherwise valid network traffic. This should be considered only after all other causes are ruled out.
Not necessarily. The code is about data quality from the Rear Lighting Control Module, so a bad bulb, socket, or wiring to a specific bulb will not normally set U0484. The code points to the module or the network feeding it.
Clearing the code may temporarily extinguish the warning light, but if the underlying fault is present the code will return. The rear lighting system should be repaired promptly because the failure can affect brake lights, turn signals, or other safety-critical rear lighting.
No. U0484 reports a problem with data received FROM the Rear Lighting Control Module, so the fault source is almost always the rear lighting module itself, its wiring, its power/ground, or the network. Replacing the PCM or BCM is not a correct repair for this code and is a common misdiagnosis.
In most jurisdictions U-codes are not emissions-related and will not fail an OBD-II emissions check, but a non-functional rear light is a safety defect and can cause a separate inspection failure regardless of the stored code.