I'm making this post only to share my experiences on my 99 LS400 with 130,000mi. When I searched the LS400 forum only two posts showed up. There are several informative posts in the 2GS forum if you can't find what you're looking for here.

I've gotten this code two different times for the same reason, but different causes.

P0171 is lean bank 1

It could be caused by a vacuum leak, a bad MAF, a bad CTS, a bad injector, a bad ecu, or a bad O2. Since the vacuum leak is easy to look for and cheap I stared there.

The first time I got the code it was intermittent and only when I was idling.

The intake resonator box had a broken nipple where the PCV on the passenger side enters the resonator. As soon as I fixed this the code went away w/o clearing the code. JB weld was my solution.


The second time months later the light kicked on at idle and stayed on.

This time it was the PCV hose on the driver’s side that had a split. So I replaced that hose that goes directly to the intake, and I replaced the PCV valve and the grommet that mounts on the valve cover. If you try and change this grommet out make sure you have a vacuum cleaner ready. The rubber was very stiff and brittle. It broke up as I was trying very carefully remove the grommet (I heard this might happen). I removed most of the thing, but the vacuum removed the rest.

I had a CTS ready to go on since I've heard these drift over time. The light didn't go off for 3 or 4 full heat cycles. I will probably change the CTS soon, but it won't be because of the CEL.

This seems pretty straight forward to me, but I would be happy to answer any questions people have.

Cheers,
M@

 

you say EGR but i'm pretty sure you mean PCV valve.... afaik '98-00 don't have EGRs lol.

also, editing your post to include the year of your LS is not a bad idea

 

Yes thanks! Fixed.

 

Hey buddy i got the same code but iam no expert, just a student with no ride.... can u tell me where the vaccum lines are located that you checked and when i say tell i would need a picture plzz if you would.

I have a timing belt way overdue but i want to start with this small stuff such as vaccum and maf etc

 

Ask and you shall recieve.

The passenger side only has the part where the PCV enters the resonator. You can see the hose disconnected in the pic.

The driver side is obvious.



Cheers,
M@

 

THx u so much

 

be careful with that PCV valve grommet, mine was hard as a rock and I would be worried about dropping pieces of it back into the head when pulling it out. I replaced my valve/grommet when i put in new valve cover gaskets recently.

 

I had a similar problem before but I had no code at all. I only had an intermittent whistle sound and the unstable / higher idle RPM. Mine is not an American model but a Japanese model and that may be the reason.

Regarding your first problem of my case, I have written here at my blog writing for my old American friends who like "Do It Yourself".
http://blogs.yahoo.co.jp/mae_yas/2547003.html

Regarding your second problem, I have posted here at Club Lexus below.
https://www.clublexus.com/forums/ls4...8-celsior.html

We had similar failures but I didn't get any codes. One more thing I must add is that the broken nipple line had no PCV valve for a Japanese model. There is just a hose in between the cam cover and the resonator.

Do American models have PCV valves for both cam cover?

 

usdm models (98-00 at least) have only one PCV valve, on the driver's side valve cover.

 

Yeah. I should have stressed this more.

I was LUCKY that I only had one piece drop into the valve cover. I checked in the shop vac and found the only piece that was missing.

 

Okey so i looked around took the cover off the engine and sprayed all vaccum pipes insight with carb cleaner but not rpm change, when i spray in intake onlly then i get rpm change but engine is loud and garage is FREAKIN COLD so i cant continue till it war up my fingers, then i will try to clean MAF in 2 sessions of warming my self

 

Update:

In the past month I've had the light come on and go out one or two times. Last week it came on and stayed on.

I had been planning on cleaning the throttle body due to a sticky throttle, but was worried I might break the JB weld on the resonator box. So this was a good chance to do that and clean the MAF (which was a bad idea, but I thought a possible cause of the p0171).

I cleaned the TB and the MAF and reset the ECU, but the code was still on. So I popped the hood and did what I should have done first: check for vacumme leaks. Lo' there was a split hose on top of the manifold that goes to the power steering.

So swapped both of the vacumme hoses that go to the PS reset the ECU and the code was still on.

I'm pretty frustraited now and decide I must have messed up the MAF so I bought the reman MAF. Installed it reset the ECU and the code is still there.

Time to go for a rip ride to let the Lexus know who's boss. I left the car idleing in the drive while I closed up the barn and returned to see the code out. Went for the rip ride and decided I may not have cleared the ECU correctly any of those times.

I put the OEM MAF back in the car and no code so far.

The moral of the story is:
ALWAYS check for vacume leaks with a P0171.
Know the CORRECT way to clear a code.
Don't clean the MAF. (The 2nd GEN GS4 writeup that's linked in the UCF20/21 FAQ says to use the exact stuff I did, but on the lable it says not to use it on a Vortex style MAF and even says LEXUS has one. I assumed if it was a write up sticky that the guy knew what he was doing (the LS400 doesn't have that style) or it would have been edited.

That's all, a warning to future readers.