O2 sensors
Hotshot
Joined: Jan 2004
Posts: 19,762
Likes: 1,079
From: St Louis
Kerry,
O2 sensors, except for the heater element, cannot be ckecked by resistance measurements.
They are voltage generating devices that, when heated, generate an output voltage that is proportional to the oxygen at the sensor element relative to a reference air sample (atmosphere).
An O2 sensor can be benchtested with a voltmeter and a propane torch to see if it works in a gross manner. Quite a bit of trouble to go through for that.
"Cleaning" an O2 sensor is seldom effective. When the element starts to get weak, the sensor should be replaced.
caskof43,
Much depends on which sensor (up- vs down-stream) is failing and what the failure mode is. Typical failure mode is that the sensor gets lazy (degraded from age) and starts switching in an erratic manner or gets "stuck" in one mode. This usually causes reduced fuel economy and, when the computer notices the issue, sets a MIL with an appropriate code. "Lean" and "rich" codes are usually due to other issues than the O2 sensors. Therefore it is important to always include your exact OBDII DTC(s) when looking for interpretation assistance. It is also very important that you fully identify your vehicle by year, exact engine, etc.
Steve
O2 sensors, except for the heater element, cannot be ckecked by resistance measurements.
They are voltage generating devices that, when heated, generate an output voltage that is proportional to the oxygen at the sensor element relative to a reference air sample (atmosphere).
An O2 sensor can be benchtested with a voltmeter and a propane torch to see if it works in a gross manner. Quite a bit of trouble to go through for that.
"Cleaning" an O2 sensor is seldom effective. When the element starts to get weak, the sensor should be replaced.
caskof43,
Much depends on which sensor (up- vs down-stream) is failing and what the failure mode is. Typical failure mode is that the sensor gets lazy (degraded from age) and starts switching in an erratic manner or gets "stuck" in one mode. This usually causes reduced fuel economy and, when the computer notices the issue, sets a MIL with an appropriate code. "Lean" and "rich" codes are usually due to other issues than the O2 sensors. Therefore it is important to always include your exact OBDII DTC(s) when looking for interpretation assistance. It is also very important that you fully identify your vehicle by year, exact engine, etc.
Steve
Last edited by projectSHO89; Aug 20, 2006 at 07:54 AM.
Postmaster
Joined: Jul 2001
Posts: 4,038
Likes: 3
From: South Kitsap County, WA
Steve-
Ok, I see your point. However, if the sensors are bad, internal resistances will be altered.
You should still be able to see if you have an open in the sensor using the resistance without the truck running, unles they are designed to indicate open... how about a multimeter on DC volts to check the output of the sensor? When you unplug the sensor the ECM will substitute a failsafe value, so the truck will run conservatively - as long as nothing is an issue upstream of the sensor, both sensors should be close.
-Kerry
Ok, I see your point. However, if the sensors are bad, internal resistances will be altered.
You should still be able to see if you have an open in the sensor using the resistance without the truck running, unles they are designed to indicate open... how about a multimeter on DC volts to check the output of the sensor? When you unplug the sensor the ECM will substitute a failsafe value, so the truck will run conservatively - as long as nothing is an issue upstream of the sensor, both sensors should be close.
-Kerry
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