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O2 Sensor reading Zero Volts

Old 03-18-2018, 05:09 PM
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Default O2 Sensor reading Zero Volts

Hello all. 2002 Camry 4 Cyl has been idling a little rough - no CEL light.

Checked several things - throttle body, MAF, engine temp sensor and others.

Purchased an OBD reader and used an app to get real time readings. Fuel trim OK but noted that the pre-cat O2 sensor stayed at 0 volts at all times, even after a 30 min drive.

Replaced the O2 sensor with an aftermarket sensor - and it reads the same - O volts.

So I'm wondering if I have a wiring prob that's giving a false indication or if the new aftermarket sensor is bad. Is there a way to check these sensors on the bench?


Old 03-20-2018, 10:50 AM
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Suspect if the sensor had 0 volts the engine would have more severe problems plus poor MPG. If MPG is normal then sensor should be working OK.

Check the following voltages at the CHASSIS wiring plug for sensor.

Voltage between red/black wire and to ground should be below 3.0V engine idling.

Between orange wire and brown wires should be 3.3V ignition switch on.

Brown wires ground the electrical shielding around the sensor wiring that goes to ECU. For this sensor, white and orange wires.

Between white and brown wires should be 3.0 volts ignition on.

For idle issues try cleaning the throttle body which seems to work for some owners.
Old 03-24-2018, 03:42 PM
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Thanks for the reply Joey - MPG is good and have cleaned throttle body (twice) with no improvement. Read following at chassis connector to upstream O2

red/black wire and to ground 2.75V engine idling.
orange wire to brown wire 8.28V ignition switch on
white to brown wire 8.78V ignition on

So two are high readings - can you interpret this - or point me to a reference?


Old 03-25-2018, 10:39 AM
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Don't know.

All voltages are referenced at the computer. Was trying to avoid having to dig to get to the computer to check voltages.

If you can, replace the brown wire referenced above to the brown wire for the sensor after the converter. This goes to the reference point on the computer.

Leave the sensors plugged into the wiring.

If engine runs normally, would state there isn't a problem. If you don't have trouble codes or pending codes might leave the situation alone. Then concentrate on the code reader for issues.
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