When the malfunction of the EPS control occurs during the LKAS system operation, it makes EPS, LKAS indicators come on. When the malfunction of the LKAS control relations, it doesn't indicate the EPS indicator, and indicate of LKAS indicator and the LKAS control of EPS is canceled. After LKAS cancellation, depending on the malfunction which detected usual EPS control by the doing, it continues and it stops assist. When the EPS indicator come on during LKAS system operation, check the DTC of EPS, and when the LKAS indicator come on, check the LKAS system DTC and it does a trouble diagnosis.