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What is a Digital Trouble Code (DTC)?

We should begin by learning about what a trouble code is. Vehicle manufacturers have placed an emissions failure indicator in the passenger compartment of their vehicles in the form of a malfunction indicator lamp, check engine, or service engine soon light.

The light is there to inform the driver that there has been an emissions related engine or drivetrain malfunction. At the same time the indicator light is illuminated, a "digital trouble code" is stored in the emissions computer indicating that the OBD-II computer has detected a problem.

The trouble code will indicate the cause of it being triggered and may include a list of component/s and/or emission system codes responsible for the fault.

Late model cars, trucks, vans, SUVs, and motorhomes have trouble codes in the thousands, though most are only accessible by the vehicle's manufacturer.

For the average home mechanic, the trouble code scanning tools sold at most local auto part stores are capable of extracting OBD-II generic codes in great enough detail to perform home repairs, given you have automotive repair experience.

Generic OBDII "trouble codes" apply to all 1996 and newer vehicles. These trouble codes were designed by vehicle manufacturers to be universal. There are manufacturer specific Digital Trouble codes (DTC) as well. Expert trouble code retrieval tools are required to extract these codes and they are not necessary to diagnose common smog check failures.

Use the OBD-II Trouble Code links below to diagnose your vehicle's codes

How to Extract Trouble Codes with a Digital Trouble Code (DTC) Scanner

Step 1. Visit your local auto part store and ask the clerk for an OBD-II trouble code extraction tool or trouble code scanner.

Purchase a moderately priced scanner. These scanners should provide trouble code data in detail, plus offer valuable tools such as check engine light resets, and freeze frame emissions data, as well as system readiness flag information.

If you are familiar with these terms, a decently priced scanner, usually around $150.00 dollars, will really help you get to the bottom of your smog check problem.

Step 2. Locate your vehicle's OBD-II Data Link Connector (DLC). The data link connecter is usually on the bottom of the driver's side dashboard. You've probably never noticed it, but it's right above your left knee.

This is the case for most vehicles. There are manufacturers who place the DLC near the center console. If you can't find the connecter in either of these two locations, check your owners manual.

Which Type Should I Choose?


The data link connector is in the shape of the letter "D", and measurers approximately 2 inches long and 3/4 inches wide.

Step 3. Remove the Data Link Connector's cover. It should be a small plastic flap attached via a plastic wire, and connect scanner cable to the data link connecter. Because of its D-shape, the connector can only be attached in one position. There is no worry of connecting it improperly.

Step 4. Turn on Scanner and wait for the prompts. You will be asked to enter your vehicle's year, make and model. Then must choose an option to perform... scan for codes, view readiness flag data, erase trouble codes, or view freeze frame data.

Step 5. Use extracted trouble codes to diagnosis the emissions component or emissions system indicated.