I've had this 2002 Xterra for a few months and after replacing the timing belt, valve cover gaskets, rear main seal, plugs, all the belts and cleaning the engine it suddenly started throwing fault codes PO132 (O2 sensor) and PO328 (knock sensor). Each time I reset the codes they would throw within about 35 miles. It has only had Shell premium fuel run through it-on it's 3rd tank. I let the fuel level run down til the low fuel light came on each time before filling. I thought it strange that both codes would throw at the same time, and after a little research found a bulletin that essentially said the two share a common ground, so we wired a common ground for the two and replaced the O2 sensor. This time I went through about 4-5 drive cycles and over 50 miles, and the codes threw again. I can't believe the 02 and knock sensor both coincidentally fail at the same time. I have read that using an aftermarket timing belt, which may have not been sized like OEM could throw the codes. Obviously the knock sensor is a time consuming fix, and I'd like to avoid that. I've read where this is not an uncommon problem, but I can't seem to find anyone who says there's a definitive fix. I'd like to keep this thing for a while, so I drove it a bunch before putting a lot of money in it, including new rubber all the way around, and after I think I've got it dependable and running right, with all the required maintenances updated, this fault codes issue pops up. Anybody got any ideas here? Thanks for your help!

Unless you have a supercharged Xterra, don't run anything higher than 87 octane fuel in it. Higher octane fuel is more difficult to ignite and the engine might not be able to advance timing far enough to take advantage of the higher octane. The higher octane fuel might be causing the O2 sensor and knock sensor codes.

VG33E engines have chronic Knock Sensor problems. It won't affect the NA VG but will hamper the Supercharged version. My knock sensor code comes back every time I clear it and so does the 03 Xterra that my father owns. The o2 sensor is something I would look into though, it's likely unrelated to the knock sensor but it does have an affect on performance. The knock sensor can be relocated if it really bothers you and I will have a write-up on this procedure coming this year once I do it to my own truck.

My Xterra has 120K miles on it. I used premium fuel because it appears it sat for a while before I bought it. My previous experiences have been to run a tank or two of premium through a vehicle that's been sitting, as the higher octane fuel burns hotter and may help get rid of contaminants. I certainly didn't intend to run premium forever. I DID replace the O2 sensor and both codes threw again within 50 miles. I probably drove it well over 200 miles before doing all the aformentioned repairs-plugs, filters, timing belt, rear main seal, valve cover gaskets, belts, hoses etc. It didn't start throwing these codes til after these repairs. I'm hard pressed to think that it would need a knock sensor AND O2 sensor at the same time-too coincidental. I have read a tech bulletin about those two sharing a common ground, and also that if an OEM timing belt is not used it may be slack and cause those two codes to trip. I'm hoping somebody out there has been through this before and has an idea. This Xterra is in great shape-been over it with a paint meter-never wrecked, the interior is mint and never smoked. It's a real keeper if I can just get past this fault code issue-hope somebody here can help?

Higher octane fuel does not burn hotter. It's better to use a PEA-based cleaner, which cleans deposits without leaving behind residue of its own. Examples of such products are Chevron Techron, Gumout w/ Regane, or Redline SI-1.

Please see NTB04-002b - 2001-2002 XTERRA AND FRONTIER WITH VG33 MIL 'ON' WITH MULTIPLE FRONT REAR O2 SENSOR DTCS, it may be applicable.

You seem to have performed NTB99-004B 1996-00 PATHFINDER, 1999-2004 FRONTIER (V-6) AND 2000-2004 XTERRA (V-6); MIL 'ON' WITH O2 SENSOR DTCs already (adding a common ground). What brand and type (splice or direct-fit) sensor did you use as a replacement?

We used a Bosch O2 sensor (Bosch makes the OEM sensor) and added a redundant common ground for the O2 and knock sensors. I work for a dealership that's big on premium fuel-probably because they mainly sell highline cars that require premium. Thanks for the info on cleaners-and yes, with the Xterra sitting for a while I should have used a PEA based cleaner. I'll drive it til I run the premium out of it, reset the codes and replace it with a tank of regular fuel and add cleaner. FYI the fuel mileage is worse than normal-even with primarily driving on the highway, and after all the work done to it's barely getting 12 MPG's. And I know fuel mileage isn't good with the Xterra-but it should be better than that.

Okay. I see no other TSBs relating to ECM reprogramming after replacement of O2 sensors. This is a strange issue indeed. You can try following the diagnostic procedure on page EC-804 of the FSM.