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Technical Resources

Wiring Diagrams

These are resources for finding the wiring diagram for your vehicle. These are quite valuable when installing an EFIE or other sensor enhancer. I personally always find one for my vehicles so that I can get to the wiring close to the computer. The access is usually much easier there, especially when considering I can find all of the wires I need in one place. I highly recommend this approach.

BBB Industries

You can often get a free wiring diagram for your sensors at BBB Industries. I have found I can usually find all of my sensor diagrams here. When you go to the site be sure to push the "Wiring Diagrams" button, as the default is to give you TSBs (Technical Service Bulletins). Here's the link: BBB Industries. After selecting your vehicle information, you'll need to select which wiring diagrams you want. For one vehicle I had to select "System Engine" and then "Sub System Engine Compartment", but for another car it was "Fuel Controls". You may have to hunt around a bit to find your sensor diagrams. There is a download limit, so if you hit that page, just hit the browser's "Back" button, and then wait a bit and try again.

Local Library

Call your local library and ask if they offer online access to auto repair manuals. Many libraries offer the service and it's free. But you must access the services from the library, not your home. That means you should bring money with you to print out the diagrams on their printers.

Repair Manuals

When I buy a new or used car, I usually buy the Haynes manual for it. Included in the manual is the wiring diagrams and the color codes for all of the sensors. I assume that Chilton's, Clymer and other similar manuals will be similar. But I have always found Haynes to be the most informative. Haynes Manuals cost $25 at their online site, and I have always found this to be money well spent. You can often buy them used on Ebay for a reduced price. Auto parts stores may carry yours also, but if not you can use the online site: HaynesOnline. There are a few makes and models that they don't cover, but in that case then just look for the Chiltons, or a Clymer (for vehicles other than a car or pickup)


To find out what kind of oxygen sensors you have, follow this link: AutoZone. Then select your year and make/model of car. Now, find the sensors and click on the links for the ones that are labeled as working on your vehicle. On the details page for those sensors, in the description, it will say either "Narrow Band" or "Wide Band". Be sure to note if the sensor is for upstream sensors of downstream. It may say narrow band for the downstream sensors but the upstream ones could still be wide band. So be sure to make sure you also get the data for the upstream sensors.

In the past, I was able to get wiring diagrams from AutoZone and other repair information. But I can't anymore. Perhaps you'll be luckier.

If All Else Fails

Use the chart of Color Codes. Remeber, these are the colors of the wires on your sensor only. Then go back to where the sensor wires plug into the vehicles wiring harness. Now you can document each of the wire colors the vehicle is using. These will be unique. Do this for all of your o2 sensors, so that you now have a chart of each sensor and the wire colors for each sensor wire. These can be used to find the same wire near the PCM (aka ECU or vehicle computer).

If you're wire colors don't match any in the chart, you can figure out which wire is which by measuring the voltages. First start the engine and leave it idling. Then measure the voltage on each wire. Note, that the sensor needs to be plugged in, so you'll need a probe that is sharp enough to pierce the insulation and measure the voltage in place. With this information you can work out which wire has which function. If you need help with this, the installation instructions for the appropriate type of EFIE will tell you what the different voltages mean. Then, be sure to find out the wire's color on the vehicle harness, and build your chart.

Other Solutions

If you have found another good resource for obtaining automotive wiring diagrams, please let me know by email and I'll post it here for others.

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