Byte 18 in VCDS long coding is often associated with bulb diagnostics, particularly in older VAG (Volkswagen Audi Group) vehicles. This byte allowed for adjustments to the “Cold Bulb Diagnosis” settings. However, in newer models, access to byte 18 has been restricted, masked with a “00” value, making it difficult to determine its original settings. This poses a challenge when troubleshooting LED bulb errors.
Attempting to modify byte 18 without knowing its original value can lead to complications if changes need to be reversed. One common issue with using aftermarket LED bulbs in VAG cars is the triggering of bulb-out warnings on the dashboard. This occurs because LEDs draw significantly less current than traditional incandescent bulbs, causing the car’s system to detect a fault.
While “error-free” CAN-BUS LEDs are marketed as a solution, their effectiveness can vary. Newer VAG vehicles often have more sensitive bulb monitoring systems, rendering some CAN-BUS LEDs ineffective. Compatibility issues may require trial and error to find LEDs that truly function without triggering errors on a specific vehicle.
Another approach involves using high-wattage load resistors (around 50W) wired in parallel with the LED bulb. These resistors increase the circuit’s current draw, mimicking the load of a standard bulb and preventing error messages. However, high-wattage resistors generate significant heat. Careful consideration must be given to their mounting location to ensure proper heat dissipation and prevent damage to surrounding components. Improper installation can pose a fire hazard.
