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Diagnosing OBD II related problems requires several things:

* A scan tool for accessing fault codes and system data.
* Access to the vehicle manufacturers service literature for wiring diagrams, diagnostic and repair procedures.
* Access to vehicle manufacturer service bulletins.

Without these three things, you may have little success repairing OBD II faults.

Technical Service Bulletins are just what the name implies -- they are service bulletins published by a vehicle manufacturer for their dealers that describe a particular problem and how to fix it. The bulletin typically includes a description of the problem, tips on how to confirm the problem, a diagnostic procedure for isolating the fault, and a factory-recommended repair for the problem. The repair may involve replacing a sensor or otherdiagnostic connector component, or it may involve reflashing the vehicle computer with revised operating instructions. The TSB will list any part numbers that are required (by dealer OEM part number). For dealer warranty reimbursement, the TSB may also include labor times and other billing information. All technical service bulletins have a number, which usually refers to the release date.

The vehicle manufacturers have published tens of thousands of pages of technical service bulletins. It would take dozens of CDs to hold all of this information, so for obvious reasons we cannot include all of this very detailed service information in this quick reference guide. TSBs can be obtained from several sources. One is the vehicle manufacturer directly. See the section on OBD II Resources for a listing of OEM websites. NOTE: Most OEM websites charge an access fee for viewing their information. But if you need the information, it's well worth the price. You can get TSBs, diagnostic procedures, repair information and wiring diagrams at these websites.

You can also search for TSBs at or These are aftermarket publishers of service information. They allow you to search all makes and models by year for TSBs and other service information. They also charge an access fee for their information.

NOTE: You won't find a TSB for each and every problem you're apt to encounter. TSBs are only released if a vehicle manufacturer sees a "pattern failure" in a certain make or model of vehicle, or its dealers need help with a specific repair procedure. TSBs are also released for factory warranty issues and recalls.

The best way to look for a TSB that may relate to a code or problem a vehicle is experiencing is to go to and search by year, make and model for any TSBs that may relate to the problem. If none are found, it costs you nothing. If you find one or more TSBs pass or fail emissions testthat may be of interest, pay Alldata's fee and download the information. A few dollars spent on a TSB can save you hours of frustration and wasted effort if a problem turns out be something others have already encountered. And for some problems, the information that's in a TSB may be the only way to repair a problem. This applies to vehicles where an upgraded, redesigned or recalibrated part is required or the PCM must be reflashed.

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