Oxygen sensor
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Senior User
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From: Brisbane Australia
Oxygen sensor
How do you test for proper operation of the oxygen sensors?
I have 4 in my '96 SOHC, that's too much expense to just relace them without knowing if they're faulty.
I have 4 in my '96 SOHC, that's too much expense to just relace them without knowing if they're faulty.
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Joined: Jan 2004
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From: Minneapolis, MN
Why do you suspect they are bad? If you have no O2 codes, I would not worry about them. If you do replace them, replace only the upstream (before cat) sensors. This will save you some $ and may help with gas mileage if you have over 100000 miles on them.
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Joined: Jan 2004
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From: Minneapolis, MN
Cargo Master
Joined: Aug 2003
Posts: 3,263
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From: BC Canada
Testing O2 sensors on the workbench.
Use a high impedence DC voltmeter as above. Clamp the sensor in
a vice, or use a plier or vice-grip to hold it. Clamp your
negative voltmeter lead to the case, and the positive to the
output wire. Use a propane torch set to high and the inner blue
flame tip to heat the fluted or perforated area of the sensor.
You should see a DC voltage of at least 0.6 within 20 seconds.
If not, most likely cause is open circuit internally or lead
fouling. If OK so far, remove from flame. You should see a
drop to under 0.1 volt within 4 seconds. If not likely silicone
fouled. If still OK, heat for two full minutes and watch for
drops in voltage. Sometimes, the internal connections will open
up under heat. This is the same a loose wire and is a failure.
If the sensor is OK at this point, and will switch from high to
low quickly as you move the flame, the sensor is good. Bear in
mind that good or bad is relative, with port fuel injection
needing faster information than carbureted systems.
ANY O2 sensor that will generate 0.9 volts or more when heated,
show 0.1 volts or less within one second of flame removal, AND
pass the two minute heat test is good regardless of age. When
replacing a sensor, don't miss the opportunity to use the test
above on the replacement. This will calibrate your evaluation
skills and save you money in the future. There is almost always
*no* benefit in replacing an oxygen sensor that will pass the
test in the first line of this paragraph.
Use a high impedence DC voltmeter as above. Clamp the sensor in
a vice, or use a plier or vice-grip to hold it. Clamp your
negative voltmeter lead to the case, and the positive to the
output wire. Use a propane torch set to high and the inner blue
flame tip to heat the fluted or perforated area of the sensor.
You should see a DC voltage of at least 0.6 within 20 seconds.
If not, most likely cause is open circuit internally or lead
fouling. If OK so far, remove from flame. You should see a
drop to under 0.1 volt within 4 seconds. If not likely silicone
fouled. If still OK, heat for two full minutes and watch for
drops in voltage. Sometimes, the internal connections will open
up under heat. This is the same a loose wire and is a failure.
If the sensor is OK at this point, and will switch from high to
low quickly as you move the flame, the sensor is good. Bear in
mind that good or bad is relative, with port fuel injection
needing faster information than carbureted systems.
ANY O2 sensor that will generate 0.9 volts or more when heated,
show 0.1 volts or less within one second of flame removal, AND
pass the two minute heat test is good regardless of age. When
replacing a sensor, don't miss the opportunity to use the test
above on the replacement. This will calibrate your evaluation
skills and save you money in the future. There is almost always
*no* benefit in replacing an oxygen sensor that will pass the
test in the first line of this paragraph.
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Senior User
Joined: Jul 2004
Posts: 358
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From: Brisbane Australia
Originally Posted by gman88
Why do you suspect they are bad? If you have no O2 codes, I would not worry about them. If you do replace them, replace only the upstream (before cat) sensors. This will save you some $ and may help with gas mileage if you have over 100000 miles on them.
The odometer has stopped at 179,000kms which is over 100,000 miles but I suspect it's done quite a bit more than that.
Thanks for the link.
The next question is, how do I pull the codes?
