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My 2006 GS300 2WD, 118k miles, is throwing a P0171 code, too lean on bank 1. I purchased a code reader on Amazon and downloaded an app to talk to the code reader. I’ve changed the filthy air filter (the dealer had left the cover in an unclamped down position after the last oil change), and I pulled the MAF sensor. I was going to clean it but it looks completely, immaculately clean inside already. I started to buy some CRC MAF cleaner but it said don’t use on Karman-Vortex sensors which it says most Lexus’s have. If the resistor looking things inside the sensor are totally clean, are there still other unseen parts that could be dirty and causing the check engine,VSC,traction lights to come on? My car runs normally when the lights are off (I keep resetting the lights) and almost normally when the lights are on. What else should I check that is fairly easy for a DIY repair? I’m ok with most maintenance things but I don’t want to get into a major DIY project since I need the car 5 days a week to go to work and so anything I do needs to be a 1 day or less project. I’ve worked extensively on my cars when I was much younger and cars were easy to fix (1960s to 1980s). I even changed head gaskets on a 93 cougar once but I’m never doing anything that extensive again. My Lexus is a black box to me, believe it or not this is the first thing that has ever gone wrong since the warranty ran out. I do recall these lights coming on when it was under warranty. Dealer changed the MAF sensor but the lights came back on 2 days later. The dealer then changed the gas cap and all was fine, so I changed the gas cap this time, first with a autozone cap, but no luck, then with a Lexus cap but still no luck.
Any advice is greatly appreciated.
Thanks
Last edited by stevewins; 05-19-18 at 06:29 PM.
Reason: Typo
I Here’s a screen shot from the software, everything passes eventually but the evaporative system seems to always be last and be the thing that sets off the codes.
You need to smoke your intake and evap system possibly a small air leak. I've noticed the purge valve hose that runs down the right (passenger) suspension tower/frame underneath the intake hose, tends to have a hair line crack at the clamp where the rubber hose fits over the hard line. can be hard to see the crack without a smoke tester.
My 2006 GS300 2WD, 118k miles, is throwing a P0171 code, too lean on bank 1. I purchased a code reader on Amazon and downloaded an app to talk to the code reader. I’ve changed the filthy air filter (the dealer had left the cover in an unclamped down position after the last oil change), and I pulled the MAF sensor. I was going to clean it but it looks completely, immaculately clean inside already. I started to buy some CRC MAF cleaner but it said don’t use on Karman-Vortex sensors which it says most Lexus’s have. If the resistor looking things inside the sensor are totally clean, are there still other unseen parts that could be dirty and causing the check engine,VSC,traction lights to come on? My car runs normally when the lights are off (I keep resetting the lights) and almost normally when the lights are on. What else should I check that is fairly easy for a DIY repair? I’m ok with most maintenance things but I don’t want to get into a major DIY project since I need the car 5 days a week to go to work and so anything I do needs to be a 1 day or less project. I’ve worked extensively on my cars when I was much younger and cars were easy to fix (1960s to 1980s). I even changed head gaskets on a 93 cougar once but I’m never doing anything that extensive again. My Lexus is a black box to me, believe it or not this is the first thing that has ever gone wrong since the warranty ran out. I do recall these lights coming on when it was under warranty. Dealer changed the MAF sensor but the lights came back on 2 days later. The dealer then changed the gas cap and all was fine, so I changed the gas cap this time, first with a autozone cap, but no luck, then with a Lexus cap but still no luck.
Any advice is greatly appreciated.
Thanks
The MAF sensor in my GS350 is very similar to what is in the Cougar. The whole car is similar being RWD and IRS. Troubleshooting tree for the engine would be pretty identical. The 95s had OBD2. The engines are more like a v6 version of the Ford DOHC, which went into the mark 8.
Just like on the Ford, if the MAF sensor was bad you would get BOTH P0171 and P0174. The MAF sensor is likely not bad, and there are easy ways to tell. I would look towards an intake or exhaust leak. The evap system can also leak air into the manifold. It may be able to be disconnected (should be a hose), you may see other codes but if the lean code goes away, that is it.
Evap and catalyst are very hard monitors to run on any car.
Try to get freeze frame data from the codes. Decent obd software should give you that info. It could tell if the problem is at idle or higher RPM.
Also, try to monitor long and short term fuel trims at idle, 1500 RPM and 2500 RPM. Do some research and report back.
Thanks, I was able to save some screenshots from the software. It does have freeze frame. Unfortunately I’m not familiar with how to use the data to evaluate the issue. I’m also not familiar with smoking the car, although I assume it means using some visual dye or something to detect vacuum leaks. Here are some of the screen shots I saved, maybe they might give you a clue.
I know some are duplicates, apologies for that, I’m doing this on an iPad and it’s not that user friendly for selecting photos since they are so small. I can intentionally get info at cartoon rpms if I know what you need to see. I really appreciate the help. I hate to go the route of just start replacing parts until I find the problem, since with Lexus that can be an expensive method. I’m not even sure where to look for all the hoses that could be leaking. I’ve barely had any time with the engine covers off so far, so I don’t know where most things are yet. Are there any good pictures showing the intake hoses, pcv valve, evaporative canister and all that? Thanks
I know some are duplicates, apologies for that, I’m doing this on an iPad and it’s not that user friendly for selecting photos since they are so small. I can intentionally get info at cartoon rpms if I know what you need to see. I really appreciate the help. I hate to go the route of just start replacing parts until I find the problem, since with Lexus that can be an expensive method. I’m not even sure where to look for all the hoses that could be leaking. I’ve barely had any time with the engine covers off so far, so I don’t know where most things are yet. Are there any good pictures showing the intake hoses, pcv valve, evaporative canister and all that? Thanks
No, replacing parts is a bad idea and I don't think the 02 sensor is bad. At idle it seems you have normal fuel trims. That eliminates vacuum leaks. But your total fuel trim on bank 1 goes above 20 in one frame.
Miles on car? When was plug changed? PCV? I don't know where the evap tube enters the engine, but if you can disconnect it, plug the port and check the fuel trims. I actually had an issue like that on my tbird recently, but it is easy to find on the PCV valve.
When the fuel trim rises (Is that at higher RPM?) That means bank 1 is trying to add fuel. You could have a low contributing injector. Here is more info, it actually comes from Ford, but it applies.
{Also, would be nice to see the freeze frame data. If you have a dongle you may be able to find an app that can read it}
Insufficient fueling: In this type of condition, the engine may actually run lean of stoichiometry (14.7:1 air/fuel ratio) if the PCM is not able to compensate enough to correct for the condition. This condition is typically caused by a fuel delivery system concern that restricts or limits the amount of fuel being delivered to the engine. This condition will normally be most apparent when the engine is under a heavy load, when a higher volume of fuel is required. If Freeze Frame Data indicates that the fault occurred under a heavy load, a check of the fuel delivery system (checking fuel pressure with engine under a load) might be the best starting point.
Examples: Low fuel pressure (fuel pump, fuel filter, fuel leaks, restricted fuel supply lines), fuel injector concerns, etc.
Exhaust system leaks: In this type of condition, the engine may actually be running near stoichiometry (14.7:1 air/fuel ratio), but the exhaust gas mixture will be lean. This condition is caused by oxygen-rich air entering the exhaust system through an external source. This condition will cause the exhaust gas mixture to be lean, even though the actual combustion in the engine may not be.
Examples: Exhaust system leaks upstream or near HO2S, malfunctioning Secondary Air Injection system.
There is a decent service manual here (not perfect, but has some good info, I looked but couldn't find the evap port): http://search.ebscohost.com/
credentials:
s8921298
password
05-19-18, 06:25 PM
P0171 code
