O2 Monitor
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Crew Cab and 356

Oxygen Sensor (O2) Monitor


Every Bus 2001

Every Bus 2002



Oxygen Sensor Monitor Gadget

This O2 monitor is a complete, functioning limited range voltmeter with a moving dot display. What you get is a printed circuit board(it is not in an enclosure), " BY 1.25" with a 10 LED display 7/16" tall. The device monitors the output of _YOUR_ O2 Sensor.If you are going to permanently install it you will have to route a wire from the engine to the front. If you pop the switch blank (Vanagon) out you will see it's hollow in the back. If you cut this rectangle on through the front the O2 monitor fits perfectly!

email me here. if you would like to purchase one to experiment with.

PRICE $22 (US)

Free shipping on all orders any where in the USofA and Canada.


O2 Monitor PCB
This is the O2 sensor gadget. P-mail me here if you would like to experiment with one. Specify if you want a green or red display.
About the Oxygen Sensor in you car.
Diagnosing Oxygen Sensors:

The oxygen sensor is really a simple device : It tells the engine computer how much O2 (oxygen) is left in the exhaust . With this information the computer can determine the best air/fuel ratio ; stoichiometry.

When the O2 sensor detects too little oxygen in the exhaust it tells the computer the engine is running rich (please send less fuel).On the other hand too much O2 means a lean mixture (please send more fuel).

The O2 sensor kind of acts like a fuel cell(a battery is a good analogy). A voltage is produced (1 to 1.5 volts) when there is a difference of oxygen levels between the inside of the sensor(the environment air) and the outside of the sensor sitting in the exhaust stream . This indicates a rich condition or to little O2.When there is O2 in the exhaust (lean), the inside and outside of the sensor has less O2 differences and the voltage output drops to zero.

BUT the sensor must reach operating temperature to work(real hot) i.e. the computer ignores any input from sensors on a cold engine. This is known as "open loop operation",the computer wings it.After the sensor heats up the computer goes into "closed loop operation".The sensor detects a lean mixture then the computer allows more fuel from the injectors. This produces a rich mixture,sensor voltage drops,computer leans out the mixture.An endless cycle. In other words the mixture never stabalizes at perfect but continuously toggles around it.

If you have a good voltmeter you should see this voltage swing from a fully heated operational sensor.

Installation Instructions

The monitor has three connections:
Your Gadget will be delivered with a printout for proper connections.
12 volts supply (switched , accessory) and ground;
Monitor input from O2 sensor output.
The circuit draws less than 30 milliamps(for fuse requirements).
I mounted it upside down i.e. solder side up so the dot representing a lean mixture is to the left and rich is to the right . Each LED represents one tenth of full scale deflection.

A little History:
My 86 Transporter developed a power hesitation when I pulled out of our neighborhood onto the main road. I had just read an article about a new voltmeter/display-driver on a single IC so this circuit was serendipitously created. I immediately found out the power loss occurred at the moment the ECU switched from open loop to closed loop operation.

Some O2 monitor observations from our VWs:

1> When the engine is first started the Dot * "floats" in the middle of it's range.
2> As the engine/O2 sensor starts to warm the Dot creeps towards rich.
3> When the ECU switches to closed loop operation the Dot swings back and forth rapidly.
4> At full throttle the Dot stays pegged in the rich zone.
5> An old O2 sensor caused the Dot to jitter and move lazily as opposed to a new sensor which gave crisp and rapid Dot movement from one end to the other.

*Dot = Lit LED on monitor display.


For safety disconnect the battery. Connect the black wire to ground and the red wire to accessory power. On my 86 I ran a single wire along a safe path underneath the vehicle and brought it into the cab through the rubber seal where the heater hoses enter. You have to drop the spare tire and look above the radiator fan to see it. From the inside I removed the center console next to the glove box to access the top of this seal. There is a plastic tab/catch on each side of this console that must be released so it will slide out. These tabs will break if you are not careful!
I only wish now I had run a cable with more conductors for future experiments/accessories.

Connecting to the O2 sensor(two possible methods):

My 85 Vanagon has a single wire O2 sensor with a female spade connector. Plugged in here is a double male spade connector (DMSC), the other side makes the connection to the ECU. I chose this connector to soldered a small length of wire because I thought it would be convenient for trouble shooting purposes.
My 86 Transporter has a three wire O2 sensor, two white wires for the heater circuit go to their own connector and one black wire to a female spade connector. Plugged in here is a DMSC, the other side makes the connection to the ECU. I made the connection here with a male/female spade connector.

I glued the circuit board into the plastic blank filling the empty switch hole below the flasher switch. I used black RTV. One customer report: do not use epoxy, it will conduct electricity and short out the board. YMMV.

O2 Sensor added to my 356.
Here I welded a "bung" on the four-to-one collector . This enables me to run an Oxygen Sensor to monitor the mixture on my 1960 Porsche.
This is a O2 "Bung">>>

They are available at Jegs.com.


An un-solicitated Endorsement

Last summer I purchased your O2 monitoring device just so I could keep
an eye on the sensor. I've owned our 87 Westy for 3 years and had no
idea how long it had been sense the sensor had been replaced. And it's
sort of neat to watch how the LED lights match the change in idle - for
example at a stop light - and how at start up how the signal tells the
engine to run rich.

Anyway, here's an endorsement worth sharing:

It was Christmas Day and the family (wife, 3year old son, & myself) are
traveling for a short 2 hour trip to the inlaws. We live in Missouri,
which isn't unpopulated, but it has plenty of country with no
population. Over an hour into the trip in the middle of the country, the
van starts hesitating - as if running too rich or too lean. The more I
push on the accelerator, the slower it goes. I glance at the LED monitor
and realize the O2 sensor is sending a constant signal; it's not running
back & forth to both sides as usual. As I pull off the road and let the
van idle, the monitor shows the O2 sensor signals lean and the van can
hardly idle (stuttering under 1000 RPM). Not sure if it's vanagon
syndrome (just worth trying) I turn the van off & wait 5 sec before
starting it up again. No change and now I have a wife with a concerned
look on her face and a son (who *always* asks "why?") is chattering up a
storm in the back seat.

Fortunately, thanks to your device, I unloaded the gifts and disconnect
the O2 sensor - putting the ECU into safe-mode. We have NO problem
getting to the in-laws and return home in the dark that night - although
as expected the mpg is lower than normal.

I MUST compliment you on your device: it saved face for me - my wife
thought it wasn't a big deal (whew!); it saved diagnosis time & money;
and it literally saved Christmas!!

In *V*anagon *W*esty love, light, & laughter,
Another un-solicitated testimonial from the Vanagon list

I have a Digitool, but for the most fun you want
Ken Lewis's wonderful little gizmo:

Last winter he made some and almost gave them away.
I don't know how much he wants now or if he has
any, but there is an email link on this web page.

I installed one as he pictures and it is lots of
fun, poking along at Vanagon speed, watching the
lights dance back and forth--or typically, with it
pegged at max because the full throttle switch is
clicked.  You can tell if the O2 sensor is working,
the ECU is controlling it and if the idle and full
throttle switches are working properly.

                        Richard A Jxxxxx

                       Boulder, Colorado