How To Understand Engine Codes

OBD (On-Board Diagnostics) introduced in the 1970s and 1980s monitor the on-board electronics which control your engine's functions and diagnose any engine problems, especially those related to emissions.

The OBD generates trouble codes that are read by scan tools; these are used by mechanics to expedite troubleshooting and repair of these complicated electronics. Introduced in the mid-1990s, OBD II offered increased diagnostic capability and extended the number of individual engine trouble codes. The OBD-computer generated trouble codes make isolating a problem to a specific system and, in many cases, a specific component in that system a snap for the professional and do-it-yourself mechanic alike.

Scan tools interpret the OBD generated engine trouble codes. The scan tool plugs into a single connector that may be located under the dash or under the hood, depending on the make and model of the vehicle. With a single connection you are able to diagnose all engine problems, as well as many problems related to other systems like the ABS (Antilock Braking System), automatic transmission, etc. The OBS scan tool plugs into a J1962 female connector carrying the trouble code signal to the scan tool via a short cable. The actual trouble code appears on a LCD (Liquid Crystal Display) as an alphanumeric readout. There are in excess of 780 "P" Trouble Codes, far too many to list here, so here's a link to a complete list of the engine trouble codes that you can print out and store in a loose-leaf binder: autowebrepair.com.

There are two basic types of scan tools: standalone tools simply offer you the alphanumeric readout; the other type of scan tool works in conjunction with a laptop or desktop PC. The former will get the job done but the latter type, like the Auto Tap OBD II Auto Scanner, offers many advantages that the stand-alone scanners don't: for example, the alphanumeric trouble code indicates that there is a problem with the throttle position sensor. To check the actual sensor, you will need to use a DVOM (Digital Volt-Ohm-Meter). If you had used the Auto Tap scanner, the actual output of the throttle sensor would have been displayed on the computer screen just as it would have been on an O-Scope screen, eliminating the need to hook up a DVOM. The Auto Tap not only displays the trouble code, it analyses the signal from the component causing the problem.