Haynes Used Car Buying Guide

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Check Engine Light Tips

1. The Check Engine light tells you the computer found a problem with your vehicle's running condition.

2. If the vehicle is driving OK, a Check Engine light is not a reason to pull over. But get the problem fixed soon.

3. In testing areas, you will fail your emissions test if the Check Engine light is on.

4. Fuel economy generally suffers when the Check Engine light is on.

5. An extended warranty covers emissions-related components that can trigger the Check Engine light. More information is at: epa.gov/obd/warranties.htm.

6. When the Check Engine light is on, one or more "trouble code(s)" are stored in the computer.

7. You can read and erase trouble codes using inexpensive code-reader tools from auto-parts stores; the tools are very easy to use.

8. The problems identified by the codes are frequently easy to fix (such as a loose gas cap), but some are complex, requiring professional diagnosis.

9. A trouble code indicates a circuit where the problem was identified, not necessarily the component itself. Diagnosis is often necessary.

10. The Haynes OBD-II Techbook (Book #10206) is your source for late-model code information. If you have a 1995 or earlier model, get Book #10205. Both books can be found in the Techbook section of this site.