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2000 RX300 check engine light

I have a code P0171 bank 1 too lean. My question is does this exclude anything that will effect both banks? If it was MAF sensor or fuel filter would it set code and say banks 1 and 2 running too lean? In which MAF sensor ohms out correctly. I cannot view fuel trim files. I have looked for a vacuum leak with no luck. I got some cigars to try to smoke it to see if there is any vacuum leaks. Trying to narrowing what i need to checks. Thanks.

My first assumption when there is only a code for one bank is like yours - I assume it won’t involve anything that should affect both banks. But that’s just for starters. I wouldn’t rule those things out entirely.

In addition to pursuing the possibility of a vacuum leak (pay careful attention to the intake manifold - not just vacuum lines), you’d want to think about the injectors on Bank 1. There are various ways of checking injector balance to see if any might be sticking closed or otherwise clogged.

Of course, at some point you have to worry about that upstream O2 sensor as well. It might be having a problem. Do you have a scantool to check out what that is doing? And maybe look at the fuel trims?


In spite of the fact that you have a P0171 code, I would hook up a scanner and look at the fuel trims for BOTH banks. It could be the case that bank 2 is not “far behind”

I’ve use the light a cigarette and blow smoke trick in the past, but a dedicated evap/smoke machine is more efficient.

By the way, are you removing a vacuum hose/plug and blowing smoke into the intake manifold?

You don’t check the resistance of the MAF sensor. You check how many grams/second it is reading

Check out this article about MAF sensors . . . I assume you have a multimeter

Do you have a fuel pressure gauge?

I do not have a scantool. I need to buy one. I used to work on my own cars, but got new car years ago. Now she got this 2000 lexus and of course it is now my problem. I was going to get the one that you can use a laptop and just buy the hookups and software. Guess that is another discussion.
I was just doing what I could before paying someone. Manual says to check resistance on terminal E2 and THA at 70 degrees F and you should have 2.21 - 2.69k ohms. I had 2.22k ohms. I will perform those other test but honestly kicked out it being mass air flow sensor cause it is only on one bank. I understand what you are sayin though and bank 2 could be border line.
I was going to put a plunger in intake and use clamps to seal and blow smoke into intake to look for leaks. I have a pressure gauge at work. Reading the manuals says I have to have special adapters to tie in fuel system to check pressure. I am sure I can figure something out with that though. Hopefully it is like any diesel and has a plug I can remove and check
pressure. Of course she has car but will let you know. Looks like fuel pressure is 44-50 psi at idle. Was also hoping that was fun too sense it was bank one. Assuming is bad but I was hoping. Wouldn’t be a big deal if I could pull into shop and work on it but not allowed to do that. Thanks will keep you guys posted.

I think it is time for a dealer visit and analysis. We had a similar code on a ford, and instead of starting a shooting match with replacement parts, took it to the dealer, ended up being bad o rings on the plenum. They claimed they had better analysis eqpt., worked for me, but a $500 repair.

I have one of the laptop based scantools and it works just fine. The cords can be had for not very much and there is at least one free software package (OBDWiz). You can get rolling for pretty cheap. But that’s to get to generic scanning capabilities. To get manufacturer specific and crack into things like ABS, airbag, etc, it costs a bundle - but mostly in software. No matter to me. It will give me live data on fuel trims and O2 sensors and MAFs and stuff. It’s well worth it, though it certainly doesn’t do what something like a dealer shop’s equipment can do.

Yea. I am not replacing anything unless it test bad. Of course I don’t have the equipment a dealer/shop has, agreed there. I don’t want to pay them for a intake manifold gasket leaking, any other vacuum leak for that matter, clog/faulty injector (I have a beaker and can test flow) etc. things that I can test my self and replace. But no I am not buying and throwing any part at it unless it test bad. Thanks


I hear you about not being able to work on personal cars at the shop

I have a nice rack at work, but I’m also not allowed to rack personal vehicles, so I bust out the jack and jack stands on the weekend

For what it’s worth, I’m 99% certain that Lexus doesn’t have a fuel pressure test port. The reason I’m pretty sure is my family and I have owned Toyotas for over 30 years, and none of them ever had a fuel pressure test port. I have a 2005 Camry, and my brother has a 2008 Highlander, and they don’t have a test port

If it makes you feel any better, Ford also got rid of their fuel pressure test ports several years ago. I have to tee into those, when I hook up my gauge at work.

Figures… Looks like I am going to have to start to buy some stuff or just take it to someone. Still got to check for vacuum leak. If cannot find nothing there might have to bring somewhere. Got to put a timing belt in this thing to.


I really feel for you now

I believe you have the 1MZ-FE V6, same as in my Camry. I just did the timing belt myself (belt, water pump, seals, tensioner, etc.) in my garage a few months ago. I was leaning over the fender and almost going blind, trying to see if all of my marks were lined up . . .


Yea that is what I am worried about. The rear cam gear lining up and the studs breaking off for water pump… I will be using the 3/4 air gun to break the bolt lose for harmonic balancer from the shop though… Well if 1/2" won’t do. Which it probably won’t.

That is the engine I have. How did you get seals out. Did you just screw a screw into seals and pull out?


Don’t sweat the balancer bolt . . . I used a snap on 1/2" cordless impact. It wasn’t a problem

I didn’t have any problems with the water pump studs

As far as the seals go, I used this set for the crank seal

I used this set for the cam seals

I suppose I could have used the master set for all of the seals . . .

I’ve never had good luck screwing into a seal and pulling it out with the slide hammer. I always wound up buggering up the seal, and it made it that much harder to remove it


Sweet. Thank You.


I was looking at proscan. Haven’t seen the OBD. Which OBD did you get? OBD link mx, lx etc?

I own this:
It comes with “OBDWiz” software which has basic functionality.

But I didn’t do a whole lot of research or anything. It was practically given to me, and that’s why I have that one. I don’t need it often, but it’s priceless when I do.

Ok. You can see trim files with that one? It looks like it, but my computer is down and using my phone. Cannot see pictures and description just says loads of useful information.

Yes. It gives fuel trims, basic O2 sensor stuff. Speed sensor reports as seen by the PCM; TPS; MAF; MAP; coolant temp; air temp etc. Most often the available PIDs vary by which car I hook it up to so to some extent, as a generic tool, what it picks up varies by manufacturer and probably model.

I can give you a recent “success” with it. I was having random power loss episodes (this was in a Ford Escort - but you can still tell when it loses power!). It was any old time while driving down the road it would just suddenly bog. I had no codes - registered or pending. So I just started driving around with it hooked up. It took a few trips, but I finally “caught” it. What I saw is the fuel mix suddenly go insanely and temporarily rich. I happened to have a set of spare injectors from a parts car. I swapped those in and that was that. Without this scantool - as basic as it is - I would have been one of those people having to throw darts in the dark while blindfolded playing games with shops who could never get it to act up for them. That one episode paid for the the thing IMHO.

Lack of success: a GM minivan with a squirrely 4t65e automatic transmission. Most of the GM transmission stuff is manufacturer specific and this wouldn’t read any of it. It wouldn’t even pull the transmission related codes because they weren’t generic OBDII codes. I was at least able to verify during this time that it wasn’t my TPS, MAF, MAP etc. Of course, that just left me at the mercy of people with Tech II scanning capability. Of course, that is more about what manufacturers try to control as proprietary and less about this tool.

But like I said, I stumbled on it and didn’t do much “shopping.” There might be low end laptop tools with better capabilities, but as I said, I think that is mostly a matter of the software. I can add on to this one 'till the cows come home if I want to spend hundreds to buy the software.

Extra unmetered air is getting into the engine, an injector is blocked, the MAF or engine coolant temp sensors are on the fritz, exhaust system leak, the fuel pressure is wrong, or the O2 sensor or it’s wiring is no good. There’s no simple way to figure it out. You just have to go through each of those one by one. Since vacuum leaks are a common thing and easy to figure out, me, I’d start there. You have to test each port into the intake manifold used for vacuum. One by one. I’ve temporarily clamped the vacuum hoses to do this sometimes. Or I’ll use a hand held vacuum pump on each device connected up to that port to make sure they hold vacuum. Probably the most common vacuum device that fails is the power brake booster, so start with that, see if it is l leaking vacuum, you might get lucky.

If it’s not a vacuum leak, this may prove difficult to find without a scan tool that provides fuel trim info. Best of luck.

George, speaking of vacuum brake boosters, you jogged my memory . . .

Years ago, one of my colleagues was battling a car with lean codes

The darn car had good power, wasn’t missing. There were no obvious vacuum leaks (no hissing, anyways), and the brakes operated normally

The brake booster was the leak, which was causing the lean codes

I must say, though, that this was in the early days of the smoke machines. They were around, but not every shop had one, and they weren’t very good, or easy to use.

It was just one of those “I’ll be darned. Go figure” repairs

And it was the shop foreman that helped the guy catch the culprit, not me. I just watched the whole proceedings.

Over the years, I’ve learned a few things just by watching what someone else is doing.

db4690 … interesting comment. Someone studying to become a physician in medical school, say they need to learn how to remove an appendix, they medical schools uses this simple process to train the student: First time the student sees this procedure done, he watches as an expert does it. Second time, he does it himself, with an expert watching. Third time, he is now the expert and doing the training of someone in phases 1 or 2.

It’s a heck of a lot more difficult to figure out how to fix cars without having someone show you how to do it the first time. DIY’ers just have to accept that they’ll usually have to trudge though the process the first time they do it I guess, as nobody is around to show DIY’ers.