Car has 300K kms. Original o2 sensors. Starts and runs fine.

A few weeks back, threw a "lean bank 1 - Knock sensor" code.
Had mechanic re-set ECU.

Last week (after 1 week), SEL comes on again.

Codes P0136 -o2 sensor Bank 1, S2 (post cat). - see P2270, P2271

Also P0325 - Knock sensor Sens 1 bank 1

In last few days have noticed an intermittent "whistling" when accelerating abouve 4k rpms under load. Can't seem to replicate this under the hood with the car parked and revving it up.

Could a vacuum leak cause the S2 to throw a code? What do the additional codes mean?
Best way to eliinate Vacuum leak before I replace the o2 sensor?

THanks

 

Check all the vacuum hoses for cracks, make sure there all secure on the nipples.
Spray carb cleaner around the engine to help determine if it's a vacuum leak.

If you can't find a vacuum leak, replace the o2 first, clear the error codes and see if the KS code comes back.

 

Thanks

Once the weather warms up a bit, I will give this a go.