Reading and Clearing Diagnostic Trouble Codes (DTCs)

Overview:

Before tuning a new vehicle, always check for diagnostic trouble codes (DTCs) and resolve as many as possible before proceeding. Mechanical issues can impact vehicle performance and the accuracy of performance data, making effective tuning challenging.

Important Notes:

Reading a vehicle’s current tune will clear all DTCs, causing a loss of valuable troubleshooting information. Do not read the tune until you have checked and documented or resolved any DTCs.

Steps to Read and Clear DTCs:

1. Connect Your Laptop:
   Physically connect your laptop to the vehicle. For instructions, see Connecting to a Vehicle.
2. Close VCM Editor:
   If VCM Editor is open, close it before proceeding.
3. Open VCM Scanner:
   Launch VCM Scanner on your computer.
4. Power the Vehicle:
   Turn the vehicle ignition to a position other than OFF. (The engine may be running or stopped, but the OBD-II port must be powered.)
5. Open a Data Connection:
   Click the Connect icon in the toolbar to establish a data connection with the vehicle.
6. Open Diagnostics & Information Window:
   Click the Diagnostics icon to access the Diagnostics & Information window.
7. Read DTCs:
   Click Read DTCs to retrieve diagnostic information. Detected DTCs will appear in the upper portion of the window.
8. Check for Freeze Frame Data (if available):
   Some vehicles provide additional "freeze frame" data for individual DTCs. If available, this can be viewed under the Freeze Frame tab.
9. Resolve Issues:
   Use the displayed information to address as many issues as possible before tuning.
10. Clear DTCs (Optional):
    If desired, click Clear DTCs to notify the vehicle that an issue has been addressed.
    
    Note: Clearing DTCs resets the emissions monitors, which may cause the vehicle to fail emissions testing until it completes the necessary emissions tests. These tests typically require several drive cycles.
    
    Note:
    If an issue remains unresolved, any cleared DTC will reappear.