failure emissions , code po325 on 1999 GMC Savana 2500

Changed the front two o2 sensor , added 93 octane gas , run fine for 10 miles , then shut off truck and then drove 5 blocks and the po 325 came right back , the truck runs good .
any ideas ???

Asked by for the 1999 GMC Savana 2500
Code PO325?? You stated "added 93 octane gas" do you have preignition (spark knock or valve ping)?
Why did you replace the o2 sensors?
I have two codes for the front two o2 sensors . no i can hear any spark knock or valve ping. no engine noises i did replace the distributor about one year ago, and set the timing at either 0 or 2 degrees with scanner.
The reason i ask is po325 i think is knock seneor related.
you are correct. i cant figure out the root cause of the problem. i replace the knock sensor, but not a OEM one .Thank you for any more ideas.
Did this happen right after dist. replacement or just recently.
no , about a year ago it started to run rough ,and i could only use 89 or 93 octane to make the truck run .
but this when the check engine light came on . dont know why ? so i need to pass the emission test to renew my license plate sticker . again thank you
1 more answer
Not knowing what engine you have, this answer is based on a 5.7 V-8. Changing the upstream O2's is a good thing. I'm sure you have over 100,000 miles. O2 sensors are like spark plugs, they should be replaced every 100,000 miles to mantain good control of the fuel mixture (gas mileage). Since gas is so cheap (yea right) you really want to get the best gas mileage.
Enough with that, there's a TSB on your trouble code. Contact me at to give your the fix.

P0325 Knock Sensor Circuit Malfunction - With Automatic Transmission

Possible Causes

Setting Conditions

•Knock sensor signal circuit is open, shorted to ground or power
•Knock sensor ground circuit is open (i.e., not mounted properly)
•Knock sensor has failed
•On modules with an integrated sensor, clear the codes and retest for codes. If the same code resets, the PCM has failed.

DTC P0327 not active; engine runtime over 2 minutes, system voltage from 10-17v, and the PCM detected an engine knock condition for over 5 seconds. The control module contains a removable knock sensor (KS) module which receives the knock sensor input. The knock sensor signal input is filtered by this module before it is input to the controls module. Spark knock is continuously monitored during engine operation. If knock occurs for longer than a calibrated time, the PCM will set DTC P0325.

This code sets in 2 Trip(s).
This code will turn on the MIL (Malfunction Indicator Lamp)