| How do I know if my O2 sensor may be bad? | If your car has lost several miles per gallon of fuel economy and the
usual tune up steps do not improve it - this *is not* a pointer to O2 failure,
it just brings up the possibility. Vacuum leaks and ignition problems
are common fuel economy destroyers. As mentioned by others, the on
board computer may also set one of several failure "codes". If the
computer has issued a code pertaining to the O2 sensor, the sensor and
it's wiring should be tested. Usually when the sensor is bad, the
engine will show some loss of power, and will not seem to respond quickly.
|
| Testing O2 sensors on the workbench. | Use a high impedence DC voltmeter . 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. |