i want to test the o2 sensors on my ford escort ('96, 1.9L), but i can't figure out which wire is the signal return.

these are heated o2 sensors. the sensor plugs are round with an indentation in the top. each one has four wires. i managed to track down the two heating element wires thru trial and error. it's the top two.

they were 6.9 and 7.2 ohms at room temp. according to the chilton book it's supposed to be in the 2-5 range. but when i tested again at operating temp with the engine running the first sensor checked out at 14.5. within the 5-30 range

i could scrap the o2 sensors just because they're out of range at room temp but they're expensive. and i remember reading somewhere that the sensor heater element is not a factor in my fuel economy problem, but whether or not the o2 signal return is functioning.

and it's the signal return i'm having trouble finding. i've tried running the voltage test on the two remaining wires with the engine running at operating temperature but the readings are just going all over the place so i have no clue which is the right wire. i'm not sure if i even have my multimeter set correctly. it goes from 200m, 2000m, 20, 200, 1000 V...

 

It should be the white wire. Use the lowest volt setting, you are looking for a voltage that wanders from about .4 to .6v, back and forth pretty quickly. If you are using an analog meter, you're wasting your time, use a decent digital meter. Once you find the signal, if it takes more than a second to swing from low to high, the O2s is going, so it should be replaced. Also, check it by backprobing the connector. If you unplug it, the computer will run full rich, and turn on the check engine light. If the light is on, it needs to be reset first so the computer will pay attention to the signal and vary the fuel accordingly.

 

i unplugged both sensors and removed them from the exhaust system. i don't have a check engine light. i'm guessing its burnt out cuz i got a lot of trouble codes. i didn't actually start the car with the sensors removed. just pulled them out to look at them, and test the heating element test. then i put them back in, started the car so i could check for signal return.

should i just delete the codes with the obd2 reader or unplug the battery for a while???

 

Unless you have a really good scanner and can log the sensor data (along with the knock sensor etc.) under actual operating conditions and know what to look for in data variance, your chance of doing an accurate test of the O2 sensors is practically nil, imo. I would just replace them with OEM or Bosch sensors.

> i remember reading somewhere that the sensor heater element is not a factor
> in my fuel economy problem

This is sort of true since the heater is meant to work when the exhaust temp. is under 600 degrees or so.

What you might do that will pay off is cleaning the inside of the connections to make sure grease or road grime is not plugging the wires since the O2 sensor breathes through the wires.