99rx

iTrader: (6)

HELP. I bought another 1999 RX300, this one only had 67k miles, and it's an AWD model. I had this problem years ago on my previous RX, but I replaced the sensors and the problem went away. So on this one, Bank 2 Sensor 1 threw a code along with the insufficient coolant temp code. Learned that those two are tied together. So I replaced both Bank 2 sensors with DENSO sensors I got off AMAZON. No problems for 300 miles or so. I bought the car to give to my grandparents who have always wanted one. So on my way to deliver the car to them, the check engine light comes on. Now I'm puzzled. I ran by the parts store to check the codes and sure enough, the P1155 and the code related to the coolant insufficient temp came back... Can anyone tell me what may be up? The last thing they want is a nice "new" suv that gets 14mpg... Any help would be greatly appreciated on this one. Thanks in advance!

artbuc

You replaced "both" Bank 2 sensors? Bank 2 only has one upstream A/F sensor.

99rx

iTrader: (6)

I replaced the one on the front of the exhaust manifold, as well as the one on the passenger side directly behind the rear valve cover area (in between the firewall and the motor). The one I bought is linked below. I read that both of the sensors are identical in terms of part #, so I replaced both with the same sensor. So maybe it's I replaced Bank 1 Sensor 1 and Bank 2 Sensor 1. Either way, I'm still getting the same code as before.
https://www.amazon.com/gp/product/B000C5YCZ2/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1

artbuc

Ok, sounds like you have a wiring issue (maybe bad connector) or faulty ECM. This is really grasping at straws, but you could swap sensors and see if you get a Bank 1 code instead of Bank 2.

Drcoffee

Im not sure what the connection is between the coolant temp and O2 sensors. Wouldnt you be thinking thermostat or coolant temp sensor?

6.0PSD

I was in a recent situation with code P1135 which was caused by a faulty brand new Denso sensor just like the one you purchased.. I was only dealing with code P0171 and decided to change out Bank 1 A/F sensor with the new one only to cause P1135... So I just threw my old sensor back on and decided to swap the two old ones, although my P0171 did come back again after a few hundred miles the P1135 never appeared again...

Tried that same new sensor at front bank 2 and immediately got code P1155 but no other code along with it... So swapping your sensors may help diagnose if there is a problem with the new sensor as it can be defective just as mine was... Could be the vehicle wiring harness as mentioned, could have rubbed up against something or the actual clip

Do come back and tell if you find a fix.

artbuc

The A/F sensor code is preventing the car from going into closed loop control. That is what causes P0125. P0125 usually (always, in my experience) presents as a companion code to A/F sensor codes.

artbuc

Yes, that is why I suggested swapping sensors. It is a long shot but you can get a dead sensor out of the box, especially when so many people return bad parts to get credits they do not deserve. Places like Amazon have extremly liberal return policies opening the way for fraud. Heck, I even got a gallon of used motor oil from Walmart. Have to check everything.

cwsteini

A 1999 Lexus RX300 with only 67K miles.. Damn! jackpot if it's in good shape

Without knowing any work that has been done to this vehicle it is really hard to say what exactly your specific issue is.., but I can confidently say that you MUST update that rear valve cover with the new one at some point, because the original is flawed and will (if it isn't already) allow oil to get sucked through the pcv ("disappearing oil syndrome") and destroy your catalytic converters (and consistent low level of oil in the engine will cause sludge) which will cause your exhaust system to super heat and your sensors (O2 and A/F) which are housed on your exhaust system will super heat and fail prematurely from this condition.

But who knows.., you could have just received a faulty sensor or the wire harness or connector could be damaged.. I cannot say.. but if everything is in tact and working properly then I would take a look and observe if there is a more systemic issue going on here.. which is very likely since this issue plagues all first gen RX's.