The subject vehicle is a '98 F-150,4.2 v-6.A friend diagnosed a bad O2 sensor on the left bank,I changed out the sensor.now he has diagnosed a bad O2 sensor on the right bank.Did one cause the other to malfunction? or just a coincidence that they both failed 2 weeks apart?
Other opinions?
Thanks!
Mike.

 

It sounds like coincidence... Another thing to think about, is that maybe something in front of it is malfunctioning. No other codes besides O2 sensor? Is it running ok? Anything unusual like it uses excessive gas? I wouldn't worry about it too much.

 

it runs great!
It gave codes 171 for left bank lean and 174 for right bank lean.
mileage is no worse than ever....16-1/2
I am gonna change out the other O2 sensor and see what happens....but those things are a bear to get at without a lift.
Thanks.

 

Does it still give you codes for both sensors or just the one now?
If it's for both then the problem is probably something that is affecting the whole engine, such as low fuel pressure, dirty MAF sensor, vacuum leak.

 

Racerguy is on the money like always. If both codes persist the problem is unmetered air getting into the combustion chamber or a fuel restricion. Follow his suggestions.

 

The first reading was a 171(left bank lean)
Second reading was 171
Changed out left sensor
Third reading was 174(right bank lean)
in between readings the check engine light would be off for about 2 days.
I appreciate you input guys!
Mike.