OilMemes

Hello all,
Though I have been reading Club Lexus forum as a guest for a long time, it is only today I finally registered as a member

I have a 2001 Lexus RX300 AWD with approx. 146,000 miles. Purchased in October of 2014 (had about 10k less mileage), can say this is one of the best and most comfortable vehicles I have ever driven or even sat in. Even drove this car round trip with my family between Chicago, USA and Toronto, Canada in summer 2015, was a very relaxing drive and I felt nearly zero fatigue either direction!

Anyway, what I seek advice from fellow RX owners with is: during this recent winter, the CEL and VSC lights have been staying on while the car is running. The code read out (as checked by Autozone, the local mechanics, and me personally with OBD2 Bluetooth adaptor and Torque app on my phone) is P0174 ("system too lean") and P1150 ("Air/Fuel Ratio Sensor Circuit Range/Performance Malfunction - Bank 2 Sensor 1"). When I brought the car to a mechanic who is in my area, he plugged in his OBD2 computer, read the codes, and told me that the codes are thrown due to the Mass Air Flow Sensor being faulty and he would change it for me if I brought the replacement to him and paid labor. According to Autozone this should be a Denso #197-6020 sensor, yet when I showed him the photo, he claimed that wasn't the right part because the sensor "should have a wire attached to it". Is he correct about this? The part that is a bit confusing is, why would the code P1150 be described as Air/Fuel Ratio Sensor (aka Denso #234-9009) on OBD2 computer database if Autozone pulls the code and determines a failure of Mass Air Flow Sensor (aka Denso #197-6020) instead? If I understand correctly, these are two different sensors with two differing functions.

My sincere gratitude in advance to anybody who can help decipher this for me.

p.s. I suppose in hindsight that the mechanic mentioned above might actually have been referring to the Air/Fuel Ratio sensor all along, which makes sense because it has a wire attached as he described and I may have misheard, but as I had that one (#234-9009) replaced already, it did not occur to me at the time to confirm that.
p.p.s. I am headed to a different garage in the morning which is a little bit farther away, I have already spoken to him and he says it is possible the codes are being thrown due to some kind of leak. I will ask for more clarification when he looks at the car. It is in fact the place which replaced the Air/Fuel Ratio sensor.

carguy07

P1150 is the Air/Fuel sensor not the MAF.

OilMemes

Thanks a lot for confirming. I spoke with the mechanic this morning, and while he had other vehicles he was working on and could not do anything for my car today before I would be due for work, he said he will take a look at the exhaust system early in the morning tomorrow to rule out the possibility of a leak allowing air to trigger P0714 and then P1150 before suspecting any sensor. I will update when I find out more.

salimshah

Airflow sensor is common to both banks, while the exhaust sensors are separate. So typically MAF will trigger both legs.

Salim

OilMemes

Salim, I have been reading posts on Club Lexus for a while, and I always have seen your informative and insightful comments on a lot of threads here.
I consider it an honor to be here with you, and I am grateful to you and the other moderators for helping facilitate such a community

I will keep your thoughts in mind today as I have my car examined.

ukrkoz

https://en.wikipedia.org/wiki/Mass_flow_sensor

Always located in primary air duct and reports general air flow into the engine to engine control module. Needs to be cleaned with MAF cleaner ONLY about every few years, as it tends to build up dirt on sensing element
https://www.yourmechanic.com/article...airflow-sensor
I had several fails on RX300 3.0L engine of MAF, every time it was rough idle.


https://en.wikipedia.org/wiki/Air%E2...el_ratio_meter
Monitors actual air to fuel mixture level.
https://www.yourmechanic.com/article...l-ratio-sensor

maxSteel

The video in this thread helped me understand the problem and resolve it.
https://www.clublexus.com/forums/rx-...uel-trims.html

OilMemes

Update: I stopped by this morning at the shop, they apparently would need to keep the car for inspection for at least the whole day, meaning it would not be a simple stop as I originally envisioned.
So while I cannot do anything today, I plan to book an appointment within a couple of weeks. Many thanks to all: I will update when the diagnosis is made.

OilMemes

Hello all,
Thought I would provide an update, as it has been a long while...

I drove to the local hardware store to pick up some painting supplies on the 28th of March. I pull out of the parking and head back home.
Suddenly, I notice that I am pressing the accelerator almost half way down, but the engine cannot go higher than ~1200 RPM. Not only is the car unable to accelerate past 10 mph, the CEL is now flashing!
*insert holy ***** reaction*
I plugged my OBD Bluetooth adapter and run Torque on my phone, getting a list of codes including P0175 [System too rich on Bank 2], P0300, P0302, P0304, P0306 [Misfires on multiple Cylinders, misfire on Cylinder #2, 4, 6] So I drove the car as gently as possible to the shop I mentioned at the top (which was less than 1 mile away from where this started. I noted the mileage as 147,213 at this time) so not really wanting to spend money and time to have another place(s) look at it, I agreed to leave the car with them. They held on to the car (Thank God we have a decent public transit system here in Chicago), and I was able to pick it up two days later on the 30th.

To make a long story short, the total of damages was as follows:
1. VVT Sensor. The shop diagnosed that the misfire on Even No. cylinders was triggered by failure of the VVT Sensor No.1. After replacing, the car runs and accelerates normally.
2. Air/Fuel Sensor. When I replaced it before at the other shop, I did not know it at the time, but that was not the Genuine Denso sensor. The shop diagnosed that first Air/Fuel sensor fault too, replacing it with a Genuine Denso one. My mistake to buy it from eBay without doing proper research what I was looking for
I'm sure you can imagine what the total bill looked like

Now, it has been nearly two weeks since these repairs were done. Not only is the car running perfectly fine, the CEL only lights up on starting the car, going out promptly.
So I think it is a safe assumption that the problem has been correctly fixed for time being.

The only thing remaining is: Since the computer has been reset, under Torque app Emissions Readiness Check (listing the status as Complete for things like Misfire check, catalyst check, etc.) all are marked Ready except for two: Evaporative Sys. and O2 Sensor, which are highlighted in red text "Incomplete". In the morning, I plan to take a long 1-2 hour road trip out on the Interstate, and see if that will cause these two to change to Complete, since that has appeared to be the resolution on many other posts here. It is really important that this be cleared, since this car will be due for Emission test in the coming year, and if they cannot change status to "Complete" then maybe the car won't pass.

I'm just thankful it wasn't something more serious or expensive, and at least there are no more DTC neither active nor pending in the system.

artbuc

salimshah

First I am human. Second I approach things with logic. I can not and do not discard good advice but logic comes more naturally to me. So I am prone to going the same logical advice. It would help me if you could please explain why.

Salim

artbuc

Lexmus

Instead of driving for hours hoping the EVAP readiness will complete, run drive pattern number 6 in the attachment. You don't have to leave the driveway. I did this when I had the P0171 code for a bad MAF and replaced the MAF. My EVAP readiness reset after about 10-15 minutes of the idling portion of the drive pattern.

OilMemes

Thank you for this guide, Lexmus.
Thing is, I was actually reading the PDF attached to the last post in this thread...
But, looking at this one and the one you sent me, they appear nearly identical

That day, I tried to do the pattern #6 from cold start, as it says. But as the guide indicated for pre-condition, the fuel should be between 1/2 and 3/4 full, and I was just below full tank, which is possibly why it did not change the status to "Completed" even after almost 30 minutes.

However, I kept my OBD reader on, and I did drive to a nearby on ramp for Lake Shore Drive, turned the engine off, and followed the steps for pattern #9 to ready O2 sensor. I didn't even need to complete the full cycle because as soon as I got to
b. Drive the vehicle at 25 mph (40 km/h) or more for at least 50 seconds. Be sure engine speed remains above 900 rpm.
I held speed limit of 40 mph for 3 minutes at ~3000 rpm and the O2 sensor flipped to "Complete" while my phone was monitoring! So since the O2 sensor is ready now, I only have the Evaporative monitor pattern left, which I will attempt sometime by tomorrow or possibly on Monday.

OilMemes

I have uploaded a screen shot from my phone showing that all monitors are ready with the exception of Evap.