Hi all ....
So my engine light went on ... after $300+ at lexus dealer, the report came back with whole bunch of codes P0120, P0136, P0171, P1133 and the recomendation is to replace 3 sensors; throttle position sensor, air fuel ratio sensor B1S1 and O2 sensor B1S2 which will cost 858.5 + tax (15% since I am in canada)... but they're not guarantee that it will fix the problem (?)

Please let me know how serious is this and what should I do ?

I have read that you can replace the parts with other brand such as Toyota etc... Please help give me advice what I should do that can save me some money

Also can can anyone let me know the parts numbers for the 3 sensors

Thank ou very much.

 

Welcome to Club Lexus. You will also find a good number of active Canadian RX300 members here, too.

I do not have specific part numbers (some other members might) Regarding Toyota parts, most Lexus parts are branded Toyota. We have talked a few times on this forum about finding certain cross-referenced parts for the 1MZE engine group (Avalon, Camry, Highlander, Sienna, Solara) that can be interchanged. In this case, you probably want to stick the RX300 specific units. Several of the other members can mention their favorite parts places.

However, let's take a look at those codes.

P0120 Throttle/Pedal position Sensor/Switch A Circuit Malfunction
In this case, the ECM looks at certain driving conditions in deciding whether their is a sensor issue. This sensor is located in the throttle body.

There 3 possibilies of problems:

1. The circuit in the sensor
2. The sensor itself (either 1 or 2 means you have to change the sensor
3. ECM (very unlikely as too many other thing would go haywire)

P0136 Heated Oxygen Sensor Circuit Malfunction (Bank 1 Sensor 2)

This is an O2 sensor. It is located after the main catalytic converter below your vehicle. Easy to get to and located between the muffler-like resonator and the catalytic converter. Accessible on the driver's side. I think some members have changed this specific sensor before and it is not to hard, BUT that might not be the issue here.

Sometimes, under certain driving conditions, this or the P0171 error (we will get to it next) can pop up and it just due to the driving condition not that the sensor is bust.

P0171 System too Lean (fuel trim) Ah my favorite Lexus RX300 error and the most common of an error that occurs. I happily get this error which tells me basically in my case, too much air for the amount of gas coming in (could even be for a split second). I enjoy this error since it means at my high altitude I am enjoying the best possible performance (at the track) I could probably get at that point in time. I got one last week when I clocked 18.198 on a wet track.

However, for the rest of us. This could mean any number of things. I have commented on them before. However, in this case it probably based on a reading rather than a faulty sensor. P0171 errors usually accompany any kind of fuel/air issue, such as the time one of my ignition coils went bust, when some of the other members had bad air/fuel sensors (those sensors just in front of the precats on the exhaust system). Thus, in this case, it cannot be tied to any specific part.

P1133 A/F Sensor Circuit Response Malfunction (Bank 1 Sensor 1) This refers to the A/F sensor that is located just before the precat behind the engine block. I will actually show pictures of where the O2 sensor is and this particular sensor in my next two posts. Several members have been able to replace this sensor.

Again, there may be nothing wrong with this sensor nor the O2 sensor after the cat. Rather, in conjunction with the P0171 error, these may come as response to the throttle position sensor error, and throw these other codes.

So what does this all mean?

My instincts would tell me to replace the throttle position sensor first and then see if any other error codes come up afterwards. Again, just my suggestion.

 

The throttle position sensor is noted in the location below, it has a connector that hooks on to it.

 

Air/Fuel (A/F) sensor for Bank 1 Sensor 1 behind the engine block.

 

The O2 sensor between the catalytic converter and the resonator.

This will look a little different since my catalytic converter is a Maganflow High Flow Cat and that resonator on the right is a Sankei off a Honda Accord (what can I say...the first car I ever drove was a 1983 Honda Accord).

 

One other thing I would suggest is to take the negative battery cable (not the EFI fuse as I usually recommend) off for about 30 minutes, then restart the vehicle, drive it and see what codes come on. Reseting the codes with an OBDII scanner will often times still not reset all the conditions in the ECM, just the code itself. Would be interested to see what comes up that time.

 

It's a lot of information for someone like me, I will need some time to digest : ).... but I just want to say thank you for help

 

Feel free to ask any questions. We all benefit from each other this way