Ben,

VW Vanagon pro book says to disconnect O2 sensor with ignition off. (this
resets the ECU) It says that oxygen sensor creates a pressure differential
which results in a small voltage signal in the range of 175 to 1100 mV (
0.175 V to 1.1 V) a high voltages indicates a rich mixture, a low voltage
indicates a lean mixture. the oxygen sensor is electrically heated (2 white
wires, ground & positive) ) to keep it at a consent operating temperature.
and a signal wire for the oxygen sensor (green (sometimes black) power is
supplied to the heating element when ever the ignition is ON.

Oxygen sensor checking:

* Engine at normal operating temperature
* start engine run for 2 minutes.
* remove hose from the fuel pressure regulator & plug hose
* CO should increase briefly then drop in value to 0.3 to 1.1 %

If NO ~
proceed to determine wether problem is with oxygen sensor or the ECU

* shut off engine
* disconnect Oxygen sensor
**** Note**** Oxygen sensor must be disconnected with ignition off. to
cancel memory in the ECU

* start engine
* Hold disconnection sensor wire to ground
* CO content must rise
If NO ~ check for continuity of wiring to ECU terminals # 2 and # 13 (this
would be pin 2nd and last in top row of plug
check with volt / ohm meter
PINS # 1, 2 3 4 5 6 7 8 9 10 11 12 13 Bold # have pin in terminal
14 15 16 17 18 19 20 21 22 23 24 25 Italic = no pin in terminal

* if continuity OK replace ECU

terminal #2 & # 13 at ECU harness connector disconnected and grounded = 0 Ohms
terminal #2 & # 13 at ECU harness connector connected = oo ohms

Mike Boland

At 02:19 AM 5/7/2002 -0400, Ben huot wrote:
>Hi guys, i receive my new Oxygen Sensor today
>
>but i don't see any difference with the old one!!!!
>
>One question:
>
>Many people are saying that an OS produce voltage when hot and unplug!!!!
>Between 0.1 to 1 volt. (rich mixture or poor mixture)!!!!!!!!!!!!!!!!!
>For now I don't agree!!!
>
>Should I unplug the battery to reset the ECU?
>
>Explanation: I get the van too normal operating temperature (OS is plug); I
>unplug the OS and test voltage to this one (ground the negative and I touch
>the OS sender wire with the positive of the voltmeter); I get about 450MV
>(it means no reading), I never get .1 to 1 volt. If i touch the van side of
>the OS wire only I get a steady .5 Volt when the OS is unplug. When i plug
>back the OS (Van running and hot) it get down to 450MV or so but sometime
>it give me a brief .7 volt and it goes back very fast to .350MV or no
>reading!!!!!. (back and forward) I never get a steady reading; yes my
>voltmeter wires are well attached.
>
>
>What are your suggestions?
>
>Best regards, Ben
>http://www3.sympatico.ca/huotx/engine1.htm
>
>Ps: I have 2 new OS sender (error from the company) and the old one, they
>all give me the same reading!!! Is my $100 voltmeter faulty!!!!