The AHLS(Auto Headlamp Leveling System) ECU detects the signal of headlamp switch which is operated by multi-function switch to diagnose the Headlamp signal line.
The AHLS(Auto Headlamp Leveling System) only operates when the headlights are On.
The AHLS(Auto Headlamp Leveling System) ECU determines whether the headlights are turned On or Off and checks signal line condition by receiving voltage value from the SJB through wiring.