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Image 1: Diagnostic Trouble Codes
When your vehicle's malfunction indicator lamp (MIL) comes on, your vehicle has stored a code that identifies the problem detected. This code is known as a diagnostic trouble code (DTC).
Diagnostic trouble codes are alphanumeric codes that are used to identify a problem that is present on any of the systems that are monitored by the on-board diagnostic system. For more information about DTCs, see the “Diagnostic Trouble Code Breakdown” section.
Pending and Stored Trouble Codes Explained
When a problem is first detected, its corresponding DTC is typically recorded as a pending trouble code. Pending trouble codes do not illuminate the MIL on the dash, so the driver is not made aware of any potential problem at this time.
If the vehicle’s diagnostic system continues to detect the same problem after multiple driving cycles, the DTC will become a stored code and the MIL will illuminate.
After you think you have fixed the problem and have reset the vehicle’s MIL, you should always check for pending trouble codes before assuming success. Just because the MIL doesn’t come back on after a few minutes of driving, it does not indicate the absence of a problem. Because if the problem still exists, it could take multiple driving cycles for the MIL to kick back on.
Refreshing DTCs
Checking a vehicle for stored or pending diagnostic trouble codes is a simple task. Simply switch to the Diagnostic Trouble Codes tool (Image 6) and click the “Refresh” button. The status of the vehicle’s MIL will be updated and any stored or pending codes will be listed along with their detailed definitions.
Clearing DTCs and Resetting the Check Engine Light (MIL)
After making necessary repairs to your vehicle, you will need to erase all stored and pending trouble codes along with all other historical diagnostic data from your vehicle. With ProScan, this task is as simple as clicking the “Erase Codes” button.
After clicking the button, you will be presented with a confirmation prompt.
Click “Yes” to erase all diagnostic data and reset the vehicle’s MIL.
Seeking Repair Assistance
As all vehicles are different, and we do not staff automotive technicians, we cannot provide repair assistance for our customers. If you are having difficulty finding the cause of a problem, we recommend visiting an online forum dedicated to your specific vehicle and asking your question there. Usually, another owner has experienced the same issue and can tell you the likely cause of your problem.
Alternatively, you can call your local mechanic, or even your dealership, and ask their knowledgeable staff about the problem you are experiencing.