Symptom: ECU upgrade in progress, error code [5021-27-7F35]
Cause: Negative response from the controller to the ECU upgrade security command
1. It is necessary to check which function of the automatic mode/manual mode was used to upgrade the ECU.
2. If it was performed in manual mode, it is necessary to check whether the ECU upgrade was attempted in a small category suitable for the controller.
3. It is necessary to check whether the car is equipped with aftermarket equipment.
4. It is necessary to confirm that there is no history of replacement of the controller installed in the vehicle.
5. If it still does not solve the problem, it is necessary to contact the controller manufacturer or automobile research institute.