Ford Repair: 97 FORD ESCORT WAGON OXYGEN SENSOR CODE, ford escort wagon, oxygen sensors

Question
OK, a panicky woman here,my mechanic who also is my uncle,is laid up from some cancer surgery,he will unavailable for weeks yet.He said the code was for an oxygen sensor(I didn't know my car had 2 of them,the guy who works for him put on the one behind the cat (he said because it looked older)he didn't do any tests to it,a few days later after getting on the highway,my service engine soon light is back on.How hard is it to check to see which one is bad and is there any possible way that even though the code say and oxygen sensor,could it be something making it show that?I know this poor car has 200,000 miles and I don't have the money to get anything else,bless my uncle for keeping the poor thing on the road this long.It had a slight vibration when sitting at stop lights.thank you so much and god bless you for helping people.

Answer
Kat-

  A problem with the O2 (oxygen) sensors usually means that they are out of their preset voltage range so the codes are pretty unique to the sensors and there's really not anything else that can throw the same codes.  The computer will sometimes throw sensor-specific codes but other times the codes are vague and just let you know that an O2 sensor is out of range without telling you which one.  That being said, they can individually be tested so the "this one looks older" diagnosis probably isn't the best way to go.  But hey...good news is that unless he improperly installed the sensor or didn't clear the trouble code (which can cause the check engine light to come on ever after the problem is fixed), you've only got one other option and that's to replace the other sensor.  Just be happy you don't have one of those Fords with 4 O2 sensors.  Hope this helps.

Steve