My 2002 Honda Accord LX, 4cyl, manual transmission reported check engine codes of P1166 and P1167. After checking into the problem, I concluded that the trouble was a bad primary O2 sensor.

After reading this web site, I immediately called my Honda dealer. They confirmed my suspicions and offered to sell me an O2 sensor for about $160. Unfortunately, when I got to the dealership, their part appeared to be used, so I declined the offer. This dealership has a policy in which they will not accept returns of electrical equipment, so I kind of wondered why they were selling what appeared to be a used unit in the first place.

When I went to a second dealer, I was asked for my VIN #. Apparently this model car is sold in two different varieties... one for use in California (a ULEV model) and a second model for use in the rest of the USA.

Ok, I happened to have a ULEV car, so I needed a much more expensive O2 sensor... Instead of paying $160 for the regular unit, I had the privalage of paying about $300 for the "UL" variety. Thank God for the environmentalists!!!

Too make a long story short, I put the expensive (UL) unit in and the codes went away. When I asked the Dealer what would have happened if I had put the low cost unit in, he simply said "the light would have stayed on". This may be the reason why so many folks on this site are having troubles even after they replace their O2 units.

The motto of the story is this... be careful to find out if you have a regular O2 sensor or the more expensive California (ULEV) model. I have the UL model and mine is designated as honda part # 36531-PAA-306. The part itself is labled "Denso 192400-1020 12C21" Please note that the wire is protected by a *green* plastic tube. From what I understand, the regular one is protected by a different color... perhaps white.

I really do hope this helps.