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Toyota Service
Toyota Service, Lexus and Toyota expert
Category: Lexus
Satisfied Customers: 4950
Experience:  30 + years of experience; Multiple Award Winning Svc Mgr; Just Answer Customer's Choice Award Winner
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Lexus With 0330 and 0171 Codes. Check Engine Light On.

Customer Question

2000 Lexus Es300 with P0330 and P0171 codes. The trac light is off, check engine light on and it wont shift into overdrive. I've cleared the codes a few times with scanner but it just keeps coming back. I have also installed new knock sensors.
What can be done to clear these codes?
Submitted: 11 months ago.
Category: Lexus
Expert:  Toyota Service replied 11 months ago.

Hello. Welcome to Just Answer. Please allow me to assist you.
On this car, anytime the Check Engine light is illuminated, overdrive is prevented. This is done by design.

The P0171 code is most likely due to a dirty Mass Air Flow Sensor "MAF")

The P0030 code is most likely due to a faulty Air-Fuel sensor 'heater'.

The P0171 code is set whenever the airflow entering the engine is disrupted. The Mass Air Flow sensor can and will get particles on it that pass thru the air filter. All you need to do here is locate, disconnect and remove the MAF. Spray the interior liberally with aerosol brake cleaner (found at any good auto parts store) and let it air dry. Do not try to accelerate the drying process by using compressed air. This will damage the MAF.

The P0030 code is a bit more involved. You are going to need to purchase and install the Bank one Sensor one air fuel sensor. This would be the first sensor on the exhaust on the side of the engine that has the number one cylinder.
Note: If you have never performed this replacement, leave this to the professionals. If you are inexperienced, and you remove the sensor, you can easily remove the threads that hold the sensor in place. This would become a very costly repair.
If you have any questions, please feel free to reply; please do confirm you have received my assistance on your request; thanks

Customer: replied 11 months ago.
I forgot to mention I have cleaned the MAF in the past, it seemed to work for a short while but then it came back. When you say air fuel sensor is that the same as the oxygen sensor?
Expert:  Toyota Service replied 11 months ago.

If you are not using a genuine factory air filter, the P0171 code will come back rather easily. If you have some type of non-factory air filter (like a K & N), this causes the light to come on very often.
The Air fuel sensor is 'like' an oxygen sensor, but the two perform markedly different measurements. The Air-fuel sensor monitors what is coming out of the engine, and the Oxygen sensor monitors what the catalytic converter is doing. They look alike but are not the same.

Expert:  Toyota Service replied 11 months ago.

Note: if you choose to replace the sensor, I would recommend you use a factory replacement part, not a 'generic' replacement part from an auto parts store. Non-Factory sensors can and will cause other trouble codes because the sensor is not transmitting the proper info to the computer.

Customer: replied 11 months ago.
Can you explain to me how this sensor causes the car not to shift into overdrive intermittently? Also, any chance you can get me a part number? Will the Toyota part save me $ instead of getting it from Lexus? Guessing they are the same part. Thanks so much, and I will let you know if this fixes the issue.
Expert:  Toyota Service replied 11 months ago.

The computer controls the Overdrive. When the check engine light is on, for ANY reason, the computer prevents overdrive by not allowing the overdrive solenoid to energize. This is common across the entire Lexus product line. A Lexus replacement part is around 250 dollars. You do not want to get a generic equivalent here.

Customer: replied 11 months ago.
how would I test to see if this part is bad?
I don't want to drop $250 to guess wrong.
Expert:  Toyota Service replied 11 months ago.

P0030: Disconnect the sensor. Measure the ohms across the two terminals on the connector side with the three ridges. You should measure resistance around 1.4 ohms

Customer: replied 11 months ago.
For the air fuel sensor could I get one for say a same year Camry to save some$$?
Expert:  Toyota Service replied 11 months ago.

The sensor costs the same for the Toyota part.


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