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Skyvisions, ASE Certified Technician
Category: Lexus
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Experience:  Lexus Expert
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Lexus ES300: check engine light..P0171..The mass air flow meter was 1

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My check engine light is on. My Lexus ES300 1999 shows codes P0125 (insufficient coollant temp for closed loop fue control, P0171 (system too lean), P1153 (A/F sensor circuit response malfunction) and P1155 (A/F sensor heater circuit malfunction. The mass air flow meter was 1.33 kohms 8F (specs are 2.21-2.69 kohms. The dealer recommends R&R A/F sensor Bank2 Sensor 1 and replace mass air flow meter. They said it needed to be done in 3 months since it "builds up carbon" but another mechanic couldn't tell me if it needed to be done in 5 months or 5 years. What's your recommendation?

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The only thing you're going to need to replace is the air fuel ratio sensor which is located in the manifold by the radiator. Make sure that you use only a DENSO air fuel ratio sensor. That is bank two sensor one. Anytime you have these three codes in combination 90% of the time it's just a air fuel ratio sensor malfunction. The other two codes are set due to the malfunctioning air fuel ratio sensor. However as a good measure it is always a good idea to remove the mass airflow sensor and clean it with electrical contact cleaner and blow dry with compressed air. There is nothing wrong with the thermostat just ignore the P0125 code.


Customer: replied 5 years ago.
Are you telling me that if I just replace the air fuel ratio sensor, my check engine light will go off? I cannot do this myself since I have no skills. I will have to take this to Firestone (or back to the dealer). How much is this going to cost me to see if the check engine light actually goes off since the dealer and Firestone say that what they think needs done is between $800 and $1000. If what you say doesn't work, then I have to pay that PLUS the $800 to $1,000. If your solution doesn't work, what is your next idea and how much would that cost?
To replace this air fuel ratio sensor is very simple to do and requires very little skill at all. Most parts store such as AutoZone sell the DENSO brand air fuel ratio sensor for around $225. If you have access to a 7/8 inch wrench and can release one electrical connector simply by depressing the lock tab and pulling the connector apart you can replace this sensor yourself. Even if you took it somewhere they should be charging you no more than one hour labor. In some rare occasions the sensors can freeze into the exhaust manifold but if you crack the sensor loose and it appears though it is starting to bind or freeze up simply stop and apply brake fluid to the base of the sensor at the threads and allow to sit for about 5 min. work the sensor back and forth and it will come right out without damaging the threads to the manifold. I have seen these combination of codes quite regular and like I mentioned above 90% of the time simply replacing the air fuel ratio sensor solve the problem. Then simply removing the mass airflow sensor and having it cleaned with electrical contact cleaner is an additional good measure. Generally this is only about one half hour worth of labor. As far as what else might be going on, it is unlikely that you will need to pursue any other avenues once you have this corrected. Once you replace the sensor you'll need to remove the negative battery cable so that you can clear the memory in the computer for the codes. There is no way this repair should run anywhere close to $800 if this is what they're charging you run for the hills.

Customer: replied 5 years ago.
Thank you for the information.

The dealer said it would be $1,000 and Firestone said it would be I think $750 or $800. I'm in Silicon Valley CA. What other choices do I have for car repairs?
Move out of California! Just kidding, very pretty state unfortunately politics, they're destroying business. If those prices were just for replacing the air fuel ratio sensor that is way too high however if they included the mass airflow sensor they are probably charging you full retail price and ridiculous labor and wasting your money on the price of the mass airflow sensor. Save yourself a pile of money borrow a wrench and do this job yourself. You could probably buy a cheap 7/8 inch wrench at the parts store.

Customer: replied 5 years ago.
Sorry, that price was not for what you suggested but what they suggested..... replacing mass air flow meter and R&R A/F sensor Bank2 Sensor 1.... whatever that means. Would you say $750 - $1000 is reasonable although on the high side for those repairs?
The mass airflow meter retails for about $180 in the air fuel ratio sensor retails for about $250. The labor would be approximately $260. This would put you at the low end of the scale. If you purchase a DENSO brand sensor from AutoZone for about $220 and then buy a cheap 7/8 inch wrench for $20 you could probably save about $500. The prices they're quoting you are on the higher end of the scale. Besides I don't believe you need to replace the mass airflow meter at least not just yet like I mentioned 90% of the time the air fuel ratio sensor will correct the lean condition code P0171.

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