Check engine light: vacuum leak
 

I brought my 1999 RX300 to the dealer because the engine check light went on and was told that it was a vacuum leak. How can I find out where the leak is?

Do you know what the code number was for the light, as vacuum leak can pop up in a number of places? One common issues is the hose that goes on to the back of the air box being lose or not attached.

Lexus Vacuum System Diagram
 

Please show me where the"air box" is in the attached diagram and how I might locate the leak. Thanks, Carl

The hose lexmex is referring to is part of the evap system and when disconnected will through off P0440, P441 and P0446 codes. This is a common problem as it is very easy to disconnect the hose when lifting up the top of the air box to check the air filter. The hose is located behind the air box and connected to the top/back of the lid. It is directly under the brake fluid resovoir. The hose connects to a metal tube about 10" down. This is where it usually disconnects.

The hose connection to the metal tube was secure. I could not find the canister to check its 2 connections. Advise me here.
Is it possible the light goes on automatically after so many miles?

Well, the light can go on for certain reasons. The most common code is the P0171 lean error, which can trigger the light. I have mentioned in the past to stop an autozone and get the code (it is free). The dealer should have given you the code number.

The other thing we do is with the vehicle turned off, pull the EFI fuse out for a few seconds. If it comes back on later, it wasn't something related to climate or air conditions.

However, if you are able to get the code, I would be more than happy to go over it with you in detail to narrow down the causes.

I don't think there is much of a chance that the hose is off at the canister. The metal tube is where it always disconnects from lifting the top of the airbox.
The light does not come on automatically after so many miles. It definetly takes a problem to turn the light on but it could be as simple as a loose gas cap. First reset the light by pulling the battery cable or fuse. If it doesn't return, you're good. If it does, it would be best to either get the code read or get a cheap reader (about $40) and read it yourself. Once you have the code come back to this forum and do a search on it for a lot of info. You could also google it for more generic info.
Can you provide any more info about what happend at the dealer? Did he just say "it's a vacuum leak" and walk away?

genijet
 

Mikey00 Thank You. I Removed The Battery Cable And It Worked The Light Wet Out. Thanks Again Carl

genijet
 

Mikey00 Thank You. I Removed The Battery Cable And It Worked The Light Went Out. Thanks Again Carl

Celebrate, when it stays off after 100 miles or so of driving.

Right now you have cleared the warning condition. The new values will be accumalated with a bit of driving.


Salim

That reminds me of something. A few times going up to the Texas border my light came on (this was when my RX was pure stock engine-wise) and then (without stopping) the light would go off. I recall reading somewhere that if is just climatological (as opposed to something really wrong), that after turning the vehicle on 3 times, that light will go out.

However, of course the magic of the EFI fuse/negative battery cable works wonders.

As Salim already said don't celebrate just yet. If it is a genunine problem the light will be back.
Interesting side note here: My wife called this morning stating that the check engine light came on on her way to work today. My thought was to go to autozone and see if they would read the code for free or buy a cheap code reader. I did a quick search and came up with some on ebay for $16.99 plus shipping. They were brand new with a money back guarantee. They were OBD II, capable of reading multiple codes, could reset the light and had 2 buttons. Some of the earlier cheap ones were lacking some of these features. Once the wife came home I did a quick check of the car and found the plastic ring that snaps around the gas cap to keep it attached to the car when it is removed for fueling had come off. The last time she got gas the attendent (no self serve in NJ) put the ring over the gas tank opening and screwed the cap down using the ring as a gasket of sorts. This must have caused a poor seal and set off the light. I didn't reset the light yet. I am just going to wait to see how long it takes to go out. There is some spec as to the number of cycles it waits.

2000 RX300

The check engine light and VSC control light have been coming on and off lately. Advanced Auto checked the codes tonight (P1130 and P1150)
Both are Air Fuel Ratio Sensor Circuit Range/Performance malfunctions Bank 1 Sensor 1 and Bank 2 Sensor 1.

Seeing it is a performance malfunction and not a response malfunction what does this mean? Also which Air Fuel sensor/s does this refer too? Any help would be appreciated.

Woods

Woods,

Will go over this in your other post in just a bit.

Saludos,

Lexmex

MickeyOO I THOUGHT I FIXTED IT,BUT THE LIGHT CAME ON AGAIN AFTER ABOUT 10 MILES. CARL genijet

That indicates you have a genuine problem. You already checked the hose behind the air box which is one of the most common causes. You may also want to inspect your gas cap real good, a poor seal could also be the cause. After that you need to get the codes to go any further. Some AutoZone stores will read them for free or pick up a scan tool. In my post above I mentioned I saw a tool on ebay for $16.99 plus shipping yesterday. That was the buy it now price and the seller had 66 of them. I went back today and I can no longer find them. What a difference a day makes. There are similar ones for $32.99 plus shipping. Harbor Freight also has inexpensive ones.

I went to Auozone and they used their OBD 2 checker and got the code: "P0171, system to lean bank (1)". They said to let it go "3 cycles" before seeing if the light goes out. I checked the gas cap seal. It looked ok but there was no pop when I removed it. After the 3rd cycle, I will get back to you. Any other suggestions?
Thanks for your continued interest. Carl

engine light on
 

Autozone used their OBD 2 reader to identify this code: "P0171 system to lean bank (1)" and said to check it again after 3 full cycles of driving and cooling.
Back passengers have noticed a significant smell of gas after a half hour drive and the light was still on. What do you think?
Carl

That is what I was talking about earlier with regard to the 3 cycles. The P0171 error is a common error, in fact the most common error.

Most likely culprit is just climatological. However, you should also consider other than the gas cap the MAF sensor being dirty. That is the little black rectangular piece after your airbox held in by two screws. If the red diode and/or the two threads visible inside the piece get dirty, they can cause MAF issues. I remember a few years back when K&N oil got on mine that was I learned of the wonderful EFI fuse trick, which is what I recommend instead of just resetting the CEL with the scanner. Best thing I find to use now is electrical contacts cleaner or if not readily available computer keyboard cleaner.

P0171 is almost always caused by dirty MAF sensor. I would clean using directions Lexmex provided. Here is also a link to a "how to" complete with pictures.
http://www.lexusownersclub.co.uk/kno...v2&id=152&c=11

I cleaned the MAF sensor as instructed even though it wasn't dirty and after driving the car for 2 miles, it went on again. I checked the fuel cap and it seems ok. But I did not get a pop when I removed it. What's next?
Carl

Carl,

What is your idle RPM when the vehicle is in D and you have your foot on the brake?

I am curious to see this as perhaps cleaning the IACV valve might be worth a shot here, if the RPM is off.

Only other thing then would be having someone with an advanced OBDII to see how the two O2 sensors before the main cat are holding up

I hate to see people have to deal with the O2 sensors. Despite no precats and using racing gas (unleaded variety, but high octane, as a cleaner) along with previously high sulfur gas, not so much as a peep out of my O2 sensors all these years, but that does not mean issues don't pop up with them.

One other thing that I know will bring up P0171 errors is fuel delivery. If there is anything dirty along the fuel lines, partially clogged injectors, you get a situation where there will be more air than gas in the air/fuel mixture and sometimes the ECM cannot adjust enough without throwing a light. It happens down here with vehicles that run the regular Magna gas, but can occur over time with other vehicles. One of my bosses had a CRV in which this occurred and we just gave it some Techron on half a tank of premium.

Sorry to hear it wasn't the MAF sensor. I once read a post by a Toyota tech who claimed a P0171 was the most common code at his dealership and 99 out of 100 times it was the MAF sensor. As Lexmex already said now it could be anything in the fuel delivery system or even one of the 02 sensors. You may want to try a can of Techron in the gas tank to clean the injectors but it is kind of a long shot. You could also have a bad injector. All this gets a little difficult for the do it yourselfer to troubleshoot.
A vacuum leak or even a exhaust leak could also be the cause. You don't by any chance have an exhaust leak? 1999 RX had that piece of flex in the exhaust up by the engine that always seemed to fail.
You never did provide any more info about what transpired at the dealer. Being that they already told you you have a vacuum leak it sounds like they did at least some troubleshooting. Did they say how much it would cost or what they would do to fix the leak?

It seems that no one caught this in your note...

Examine the rubber seal on the gas cap. After a short drive with right and left turns (to slosh up the gas in the tank, use your sense of smell.

Emission testing facilities also have a set up to check that the gas cap is working fine and for a small fee they can check it. If dealership is near bye take the cap in to the parts counter and let them take a look.

It's not that no one caught the gas smell reference in the post, It's that we know it's not the gas cap due to the P0171 code. The gas cap would be P0440 or 442. It's most likely caused by a sensor delivering too rich a mixture or maybe even a leak or something else after the fuel pump but most likely not before the fuel pump.

Engine light on
 

I had a auto shop fix it and he found the Oxygen sensor bad.They replaced it and the car runs good.Thanks for all your help, I hope this info helps others. Carl genijet

I went to a local shop and the repaired it by replacing the oxygen sensor. Thank you for eveything. Please pass it on

Lexmex,
Thanks very much for the tips. My Es300 had "check engine light" on for a while and the gas mileage was not as good as before. I followed your tips and found out couple of hoses which connected to the airbox were loose.
After tightening them up and resetting the engine light (unplug battery), the problem went away. Gas mileage improved (over 500 miles test).
Thanks again for the great advice.

hi I am new and have a check engine light problem code 440,441and446on my 2002rx300.Can you give info on this

hello again i looked good after more reading in this wonderful forum i had a disconnected hose behind air box .Thank you

So, I too am going through this situation. PO171 code with my recently purchased 2000 RX300 with only 67,000 miles on it. I've cleaned the MAF twice this latest time with a q-tip. I reset the CEL and everything is good, but then after a week of driving the light came on again with 171. Power seems to be fine, then again I don't know since I just bought the car a few months ago. Not losing mileage either. My next step is to check for vacuum leaks. Also have an aftermarket MAF sensor coming. Fingers crossed...

I had P0171 and tried cleaning the MAF without success. Replaced it and all is fine. They do go bad. Very common. cleaning is the first step but it doesn't always work.

Man, installed the new MAF sensor and the Check Engine light came back on again after about 100 miles of driving, then it went off again without resetting then this afternoon the error came back again. Is there a DIY vacuum test post somewhere? I just need to know where the vacuum is located so I can spray some brake cleaner. Thanks.

Is the brake cleaner safe to be introduced in the vacuum line?

Salim

Gas Cap defective.

Saw it on a few forums and videos online that used the brake cleaner. Supposedly the idle will go down if there is a leak.

Going to replace the air filter with an OEM one. I noticed the light after my wife went to Walmart for an oil change. She mentioned they changed the air filter. If that doesn't work I'll change the gas cap.

BTW, the light seems to come on when I am accelerating on the freeway.

Oh, I checked the often mentioned hose that's behind the MAF and it's connected.

That would be carb-cleaner and not the brake cleaner. Depending on where you squirt it, make sure it is safe for sensor. With carb cleaner, the rpm will go up.

Salim

Check the vac pipe is connected to the air box. It can get dislodged when the box is messed with.

Salim