RXy

Recently replaced B1 S1 AF Sensor ( stock Toyota Denso). Now I am getting an intermittent issue. Upon start up the car is running lean on B1 S1 for about 5-10 minutes. During this time ST Fuel trim is indicating 19.5 LT is "normal" on occasion I will get a P0171 ( 1 time a 1130), but not always . After up to operating temp all is good. Fuel trim is spot on for both banks. Bank 2 fuel trim is well within normal range. Start up idle is around 13-1400. When warm around 600 at idle. Any suggestions? Recently I checked and cleaned PCV, OCV, OCV filters, MAF, TB., changed the oild / filter. Checked all the hoses etc. and they seem in place, but have no done a vacuum test. After warm, it runs beautifully and continues to do so the rest of the day. I am not sure what this indicates, so I'm throwing it out to those much wiser than myself. Thanks

Lexmus

If the Short term trim is that high, your long term trim should be rising to compensate. Also, if you get a code P0171, your LT trim has exceeded 23% (or thereabouts), so your LT trim is not normal.

What made you replace the AF sensor in the first place? Did you buy the sensor off of ebay or from a reputable seller? It seems like the new sensor might be bad since you go from normal to very high bank 1 trims at the same engine conditions.

RXy

Thanks Lexmus. Replaced 1st due to P1130 / PP1135. Passed emissions in CA, BUT you are right ST FT being high should being compensated in LT FT, so that is definitely not normal. B2 is still solid and usually and both ST and LT are not + or - by much. Strange that after 5 min or so it behaves well.

As for purchase - Guilty! I did purchase on Ebay. I thought I purchased a genuine Toyota / Denso AF Sensor even came in the Toyota box, stamped w/ Toyota Denso 89467-48011.

Is there a good place / vendor to buy from besides the dealership for a reasonable authentic part? Any suggestions? Also, does it matter if it is the OEM Toyota / Denso 89467-48011 or the Denso 234-9009 ? I've read and heard some people claiming only the Toyota/Denso version works right. Well on the bright side, changing it will be easy now that I've got some experience doing it. The first time through unplugging the connector was tricky! Thanks

maxSteel

Oxygen sensors need to heat up before they are accurate. Maybe the replaced one is taking longer to reach operating temperature.

RXy

That's what I thought too, but these AF Sensors have a heater circuit so I am guessing it should be nearly instant when the vehicle goes into closed loop operation to use the AF sensors.

maxSteel

They do, but the replaced one may have a deficiency in the heater, a difference in the heating time, or maybe some other material difference causing it to take longer to be operational. It's not throwing a heater circuit malfunction though. The diagnostic manual indicates the sensor should be warmed up after running the engine at 2500 RPM for about 90 seconds

If they wasn't such a pain I'd swap them and see if the problem shifts.

RXy

Yes, something is causing this one to lag and now possible fail. Today it started functioning fine, but had a momentary lapse after about 10-15 min ( I have monitoring with my scan tool while I drive since the change) giving me a PO171 and P1130. At the same time ST (19.5) and LT (52) fuel trim numbers went high and lean for a few seconds. I think this indicates a failing AF Sensor. I could feel the hesitation on the freeway and got off immediately. Luckily I was about a mile from my office.
I may swap them when I have time in a day or so to try to confirm the AS Sensor issue. Doing both will require some patience and anti-seize. Until today it lagged only when cold, but today it got me when it should have been warm.

Lexmus

Definitely sounds like a bad sensor. If you buy another, I would get the Denso 234-9009 from Amazon. Right now it is $119 from them (not third party seller).

Another alternative is to buy it from Advance Auto online with pickup from store and use a coupon. You might get a comparable price and be able to get one immediately.

RXy

Are Amazon sensors like this the real deal? If so great, just a little skeptical now. I'll check to see if AA has them in stock. Thanks

carguy07

They have been fine in the past when Amazon was the seller. I wouldn't try any of the other re-sellers on there.

RXy

BTW I checked them out on Amazon and bought through my local Walmart. They carry the identical Denso 234-9009 and price matched to Amazon. That might help some people. They will deliver or you can pick up in store. sometimes I like a physical address to pick something up or return it. I 'll be in there picking up stuff to do an oil change on my wife's car anyway. it has been running fine, but not driving much until I change out the sensor. Thanks for your advice. I'll keep everyone posted as to the results.