Re: Bosch O2 sensor

[Simon Favre <simon@xxxxxxxxxx>]

All Lambda (O2) sensors work the same way. The 3 (or 4) wire units merely
have a heater coil to get them up to operating temperature faster. With
these, you have to know which wire is actually the signal wire. Assuming
you can get this off the wiring diagram, you connect a DVM between this
wire and ground. After the car is warmed up, you should see the voltage
jumping back and forth between about 0.2 and 0.9 volts. A steady reading
usually indicates a bad sensor. The problem could be elsewhere, as the
O2 sensor only gives the EFI system feedback about what it did to the
mixture. Current systems use the sensor as a switch. They let the air to
fuel mixture wander back and forth across the ideal point using the O2
sensor as a trip point detector. If something else in the system has it
pegged on full rich, the O2 sensor will appear to give bad readings.

There is also a way to test the O2 sensor on the bench, out of the car. 
You clamp the hex nut part in a vise, connect the DVM between the signal
wire and the vise, then heat the sensor tip with a Propane torch. The
voltage should rise to about 0.8-0.9 volts, falling off rapidly as you
take away the flame. You have to heat the thing up cherry red, but once
hot, it should respond rapidly to more flame or less. Slow or no response
means a bad sensor.

John Davis wrote:

>I've read in recent digest about verifying if the O2 sensor is
>working properly using a DVM to check for oscillating voltage...
>
>Does this apply to a Bosch 3-wire O2 sensor as well? Can 
>someone please give details on how this is done and what 
>to look for.

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