I am working on a friends 99 forester and the car threw the code P0170 for fuel trim. I checked with a subie mechanic and he told me to replace the front O2 sensor. I did that and cleared the codes. Now I am getting a P0130 front O2 sensor and the P 0170 code. What did I do wrong and What should I look at next?

 

Thanks guys.

I don't think the front O2 sensor was defective, I would put the original back in then go after the Lean P0170.

 

The 99 was a MAF engine and each time I troubleshot a P0170 it turned out to be a vacuum leak. So I would check hoses and their seating. It could also be the MAF needs cleaning also, so a can of CRC MAF cleaner is a cheap fix to try.

 

I DID have 2 that along with P0170, the cruise didn't work. The vacuum hose, at the cruise actuator, was off. That's mounted on the passenger side firewall, and when that little hose comes off, many times you will not even notice it unless you are looking for it.

 

Good luck.

That is a good suggestion. I will look at the lines this weekend. Thanks