The 20 lamp precision oxygen sensor indicator; AutoSense Model 302 for factory and after market oxygen sensors of the 0 to 1 volt variety.

Auto-dimming 20 lamp guage -- $56 plus shipping

Also available:

Standard Motor Products generic single wire O2 sensor -- $28

We also have K&N sensor bungs to be welded or brazed into pipes and the mating plug for securing the hole when no sensor is installed (not needed if you plan to keep the sensor in all the time).

K&N 85-21688 sensor bung -- $18

K&N 85-21686 hole plug -- $24

Blu Mol Hole Saw mandrel and drill + Spartan High Speed Steel 3/4" (19 mm) saw or the same thing by Lennox for the right size hole in a header or collector or reducer. The works: Drill, mandrel, and hole saw is $22 assembled when ordered with your Model 302.

Hole saw -- $22

We are not in the tool business and pass these along as a favor. You can probably save a few bucks with a couple of calls and a trip to the bolt and machinery shop. The K&N parts are sometimes nearly half price on sale at auto parts stores. We include the manufacturer's part number to make it easy to check around. Just remember, you can save time and effort by geting it all in one package from us, and we all want you to have a good experience when we work on our cars!

Go to Disclaimer -- Please read

The AutoSense 302 is a 20 lamp mixture display that works with any of the standard auto 02 sensors. [ Zero to one volt output with 0.476 volts = 14.7/1 ratio] They can be original equipment or installed in headers or collectors or reducers on performance vehicles.

Light sensors keep brightness comfortable day or night. Right ten LEDs are red, left ten are green.


Wiring is hooked up with the help of the included three wire plug-in connector.

The side facing the viewer is black, but the side facing away

has three screw down type wire clamps that work with solid or stranded wire. For this application it is best to use stranded wire with the ends tinned with solder.

If the wiring is short or hard to reach, it is easiest to wire just the connector. You can get a better grip if you have the room by plugging it into the display first and turning it face down.

However, if you want to absolutely make sure you do not mar or ding up the display, do the wiring to a separated connector.

Power for the AutoSense Display.

You will need 12 volts and ground for your AutoSense Display. It is easiest to hook into the power controlled by your car key switch (as opposed to putting in a special switch). For example, the +12 volts going to your radio is usually convenient but starting from the fuse box is better. If you use radio power, then use a separate ground. The power drawn by a radio fluctuates with the volume and sound and the current flows back along the ground wire - so the ground wire at the back of the radio is unlikely to be at the same ground potential as the computer or O2 sensor. A self heating sensor needs to be powered independently.

Installation in a system using an existing oxygen sensor.

Your car's O2 sensor will be in or near the exhaust manifold so that it can heat up quickly. It looks a lot like a short spark plug. You will have to tap into the wiring and it is best to do this at least 18" away from the sensor. Keep the wiring away from the exhaust manifold and other hot parts.


Using a General Purpose O2 Sensor on a Performance Motor.

You can mount an O2 sensor in the header or collector or reducer piping of any motor. Since the sensors don't work till they reach about 800 degrees F, you will need self heating sensors (3 wire or 4 wire sensors are self heating) for mounting more than a few inches from the exhaust ports and for reliable readings without a long warm-up. Bosch has a replacement heated sensor that fits the bill. The sensor must be powered from switched power. Since the power is only used for the heater, the sensor power wires do not have to reach the AutoSense 302 Display.


Any muffler shop should be able to weld threaded sensor adapters called 'bungs' into a hole in a header or collector or reducer. We prefer the reducer, which is a lot cheaper to replace than a header!

Here is a view of a header collector on the left and a reducer (3" to 2-1/2") on the right. The reducer is only about 4 inches long and easy to handle. We drilled a hole with our drill/hole saw combination and had the bungs brazed by the same shop that then welded the collector to the main exhaust.

Important tip: Make sure the person who does the brazing or welding keeps the loose 3 bolt ring in place while installing the bung. You most likely will not be able to fit in on after the bung is in place!

This is on one of our test vehicles - a '74 Jimmy with a square port 396 from a '69 Malibu or Chevelle - so there is plenty of room to orient the bung and sensor straight up. Be sure to figure out the positioning you need BEFORE the reducer is welded in place!


Important tip: The sensor compares the amount of oxygen in the piping to the amount in the outside air. If the sensor is clogged up with dirt and/or oil around its body, it will not function correctly. Try to position the sensor to avoid road dirt and engine oil yet be reachable for cleaning. Also the positioning is important to avoid rocks and gravel,etc.

The highlighted area above shows the view of the sensor on the reducer as seen from the engine compartment. As you might be able to tell from the shot below, we had these bungs brazed instead of welded. If you are racing or running very hard or high horsepower, high enough to turn your pipes red hot, this must be welded. Brazing will soften or melt.


Important tip: Use anti-seize compound on the bung threads. The sensors can be replaced with threaded plugs if they are only used for tuning. Use anti-seize on the plugs and sensor threads.

Note: Our high speed steel hole saw should be used with plenty of cutting fluid or water - keep it cool. The saw cuts through header and collector tubing with ease and leaves a very clean hole.

You can save the trouble by getting ready made collector/reducer fittings like those from Flow Tech. Flow Tech has sizes 2-1/2" to 2-1/4" reducer and 3" to 2-1/2" reducer.



Yes, that's right, we have a disclaimer!

The face plate of the Model 302 is marked off in Air/Fuel ratios from 12.5/1 to 17/1. This is what you will see on other manufacturer's units. It is also what is described in many automotive and performance books. However, only the center number is likely to be accurate.

First, we should really be calling your O2 sensor a relative residual oxygen sensor. The voltage is related to the ratio of the amount of oxygen outside the exhaust system to the amount inside. That is why there are little slits in the side of the O2 sensor on the outside, so outside air can circulate through the sensor.

Second, the output is shifted somewhat by both exhaust gas temperature or sensor temperature and exhaust back pressure.

Third, the output is not a nice linear relation to the O2 level and can vary rather wildly from maker to maker. So what good is it? The center portion labeled 14.7 is always going to be very close to correct. This is the output value used by engine control loops. You can see how at idle the computer varies fuel flow to make the mixture "hunt" back and forth and keep the 14.7 "ideal" crossover point in the middle, usually by keeping the time spent on either side equal.


The Model 302 is really a voltmeter calibrated with the centerline BETWEEN the green and red lamps to equal 0.476 volts. There is enough variation in the O2 that both lamps will be on when the O2 sensor puts out that voltage. The display shows 0 to 0.9 volts left to right. Though the 14.7 in the middle is accurate under ideal engine, temperature, and pressure conditions, the labels for 17/1 and 12.5/1 are just suggestions of the limits produced by O2 sensors.

So what do you use it for?

If you are a performance enthusiast, readings on the display can be matched up to spark plug color readings. In this case the high precision 20 lamp display helps out.

The response of the Model 302 is fast enough to see a bad cylinder at idle. It will be a flickering or dim lamp set apart from the average value. If you adjust valves with the engine running and hot as is sometimes called for, you may be able to get some help from the display in finding a misbehaving section. At this time we don't know what effect the back pressure from crossovers has on this process.

You can also watch your driving habits. Sudden advances of the throttle cause a normally aspirated engine to go completely lean as the wider throttle opening lets the air come in SLOWER and it takes a moment for the extra fuel dumped by the accelerator pump to reach the cylinders. This happens fairly fast but is easily seen. A jump to wide open throttle will cause the engine to go lean and you can watch as it comes back to equilibrium under max power. You can get used to the operation of your particular O2 sensor and notice when something changes, like a backfire in a Holly double pumper that damages the power valve or a hole in an accelerator pump diaphragm, air leak, etc.

For driving with a normally aspirated carb, you can see what normal behavior looks like as you drive. If anything goes wrong you will see right off it is fuel/air flow related. For example, a gasket leak or hole in a vacuum line. You also may be able to see the throttle setting for max power at a given RPM. For instance, if you are towing a load up hill and advancing the pedal slowly and the mixture is getting richer, you will hit a point where more pedal doesn't mean more power and doesn't change mixture (or less vacuum, if you have a gauge). You can back off till the display shows a slight move toward the lean end and save fuel and fouling.

In a modern computer controlled or fuel injected car, the display can show you immediately if your O2 sensor has gone bad or been contaminated as well as how long it takes to heat up. If your car uses a self heating type (HEGO) you will be able to tell if the heater has burned out if it takes a long time to heat up compared to normal. If you get reasonable readings but no "hunting" there may be a problem with your computer.


Note: This unit is for hobby use on road vehicles, boats, and stationary engines.

Not for use in aircraft. Some homebuilders or ultralight owners may be tempted to use them as a failure indicator.

The Model 302 uses 12 volt power , is not fused inside, and is not made of self-extinguishing materials.