Wide band oxygen sensor controller

Last update: 3/7/10

LSU 4.2
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A wide band oxygen (o2) sensor MUST be connected to a "controller" or what some people call an "adapter", "control module" etc to be able to use it. You can not just connect the sensor to your car battery to heat it and try to use the other wires to connect it to an ECU  etc.

The o2 sensor has electronics in it that must be maintained at a controlled high temperature. The controller has the drive circuitry to properly heat the sensor and convert the readings from the sensor to allow other devices to use the information.

In operation, the hex portion of the sensor will reach temperatures as high as 500 C (932 F)!!  Be careful even when testing the sensor in air. It WILL burn a hole in your skin or the work bench!

Where to get information about sensors, controllers etc:

There are many websites that can give you bits and pieces of information. I've found this site to be one of the best to get the most information at one place:


Bosch Motorsport has a "Technical Customer Information" .pdf file that gives the complete specifications of the LSU 4.2 wide band oxygen sensor.

This link,  Y 258 K01 005 000e  is another document that has the specifications of the LSU 4.2 in a different format.

Where to get a o2 sensor and controller:

There are many ready to install units available on eBay, in auto parts stores (high priced), on the web (low to high priced) and several companies sell kits (low to medium priced) to build your own controller.  Probably the most common 5 wire o2 sensor to use is the Bosch LSU 4.2,  p/n 17014 (Bosch OE # 0 258 007 057) as used on some Volkswagens, p/n 021-906-262B.  Be aware that some other Bosch units are electrically the same but have a different p/n due to the cable being a different length. Controllers come in various sizes and have various features. Some can do data logging, others can drive a display etc etc.

The best idea is to choose a controller with the features you want and then see what sensor the seller recommends. Sometimes it's cheaper to buy the sensor elsewhere (don't forget s/h charges). Other times ordering the sensor and controller from one source is best

At the time I bought my units it was more economical for me to buy my o2 sensor through Amazon.com and a DIY kit version of the controller from   14point7.com

At that time the JAW 1.041 w/display was the current controller. This controller is very good and can do data logging to your computer or laptop through the serial COM port.

Update on 3/7/10
The JAW controller has been discontinued but there is a much better controller being offered now. The new controller is called SLC DIY. The data logging features are slightly different from the JAW but the specs of the unit are even better than the older model. The data logging and setup is done through the USB port of your computer/laptop. This unit comes with a built in large LED display and the case.

The owner of the company is active on the companies forum and is very helpful in answering questions etc. You can now buy a combo DIY kit from them that includes the o2 sensor, the special mating connector, the controller with the display at a good price. And since the parts all come from one company you know they will work together. Every thing you need to build the controller is included except the solder .

To see an enlarged view of most pictures, left click on a picture or right click and select "View Image".
contoller kit parts

These are the complete set of parts you use to build a JAW 1.041 o2 sensor controller. Each part is bagged and marked with the value. The PCB and part quality is superb. (No, I don't work for them.)

You do have to source your own case. I used an old aluminum garage door receiver case for my case. I also used sockets on all the ICs. The kit supplies a 20 pin socket for the uP.

The heater control IC does get quite warm and you have to get rid of that heat. I mounted the supplied heat sink to my alum case for additional heat dissipation. The case will be mounted to my alum firewall.

display kit parts

These are the complete set of parts to build the JAW AFR display unit. They are included in the basic and combo JAW kit.

The 7-segment display numbers are 5/8" tall so they are very easy to read. There is a control for brightness on the PCB.

The only thing you have to supply in addition to a case, is some ordinary 5 conductor cable. Computer ribbon cable works fine.

Both boards can be built in a day or so if you are familiar with electronic kit building and soldering.

The SLC DIY kit includes a case and has a few different parts.

complete sensor controller

Here is the controller all built with temporary cables for testing on the car. The cigar lighter plug uses a thick AC line cord for the connection. The unit draws about 1.7 amps maximum from the car battery.

The main PCB is 3" wide to give you an idea of the size. By pure luck it fit my case perfectly. The cover isn't shown in these pictures. The heat sink is included with the kit. I added my own smaller "U" shaped heat sink to the voltage regulator.
controller tied to dash
Talk about temporary mounting! The controller is tied to the top of my instrument pod with some string and is ready for it's first test on the car.

The unit worked perfectly the first time! Of course I had already tested it on my bench so it wasn't that big of a surprise. The DB-9 COM connector is used for loading options into the controller and data logging on your computer. The program is free on the company website.

Sun vs JAW

This picture shows my 1954 Sun Air Fuel Ratio meter and the JAW to give you an idea of what 61+ years of progress looks like. The Sun was the latest-greatest aid for tuning cars in it's day.  This one still works!

The lower "meter" on the Sun is the "booster pump" that draws exhaust gas into the unit through the rubber hose for measurement. As were the safety concerns of the day, the exhaust is then dumped out of the case through a short hose on the rear of the meter case into the area where the meter is situated. Like in your LAP if you are driving around!  Best you leave the windows open while using this meter!

Notice the two calibration knobs and the function switch on the Sun unit.  Surprisingly it gives quite accurate readings compared to the JAW unit. Of course the JAW is more accurate and has many features that the Sun can't duplicate. The JAW and sensor are calibrated as a unit when you test it with the free software that you download from the manufacturers website.

The Sun is -very- slow to respond to AFR changes due to the 15' of rubber hose that connects the pickup (the ray gun looking thing at the bottom of the picture that is shoved up the exhaust pipe) and the main unit. But it was better than sticking your finger up the exhaust pipe to check for a rich mixture. Although the finger method and a little spit still works for checking if an engine is using oil.