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Check Engine Light Codes for Toyota

by Kelvin O'Donahue

The check engine light is controlled by a diagnostic computer that monitors sensors located throughout a vehicle's mechanical systems. In case of an abnormal reading, this warning light alerts you that the vehicle should be serviced.


On-board diagnostic computers began appearing in vehicles in the late 1980s. Starting in 1996, an OBD-II (on-board diagnostic, 2nd generation) system has been required on all vehicles sold in the United States. All OBD-II-compliant vehicles share a basic set of codes, which must be read by a scan tool. Many vehicles also have manufacturer-specific codes as well.

Pre-1996 Codes

OBD-I (first-generation on-board-diagnostic) codes were not standardized from maker to maker, though a few post-1994 vehicles are equipped with an OBD-II-compliant diagnostic computer. To retrieve an OBD-I code, a mechanic must jump two terminals in the check engine connector and observe the check engine light to decode a pattern of blinks.

OBD-II Codes

All post-1995 vehicles, including Toyotas, share a common set of diagnostic codes. These are five-character codes, one letter followed by four numbers in which the first number is a 0 (zero), such as P0171. Toyota also has a subset of manufacturer-specific codes, in which the first numeric character is a 1 (one), such as P1406.

About the Author

Kelvin O'Donahue has been writing since 1979, with work published in the "Arizona Geological Society Digest" and "Bulletin of the American Association of Petroleum Geologists," as well as online. O'Donahue holds a Master of Science in geology from the University of Arizona, and has worked in the oil industry since 1982.

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