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lexpert, Lexus Master tech
Category: Lexus
Satisfied Customers: 2100
Experience:  Master Certified with lexus, 8 years experience with Lexus
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2002 Lexus RX300 fault code P0174. What is the procedure to

Customer Question

2002 Lexus RX300 fault code P0174. What is the procedure to check probable cause " Lean Air / Fuel ratio - fuel injector or vacuum leak. I already understand how to clean the MAF and change the oxygen sensor. But do not understand how the check the first probable cause (Fuel injector or vacuum leak).
Submitted: 1 year ago.
Category: Lexus
Expert:  karrs2fix replied 1 year ago.

Do you have the ability to monitor engine control module data with a scan tool ? Maf readings , O2 , Fuel trim values?

Expert:  karrs2fix replied 1 year ago.

A good visual inspection for any air intake or vacuum hoses disconnected in the engine compartment can contribute to the fuel system lean codes. Most common issue is a dirty or defective mass air flow sensor.

Customer: replied 1 year ago.
I do not have the scan tool available. Is this something that AutoZone, or other store may provide? Or, I might purchase the scan tool - is it the same tool used to read the faults? I will first clean the MAF later today, and clear system by disconnecting the battery. However, I see the first probable cause is the fuel injector / vacuum leak. I assume since this is first on the list, it is a higher probability cause than the MAF.
Expert:  karrs2fix replied 1 year ago.

Those lists provided by some parts stores can be miss leading. Those are possibilities that can cause those codes. They are not very common, I have had very good success in cleaning the MAF sensor. Make sure you use specific maf cleaner as you can damage the sensor if there are excessive lubricants or solvents in the cleaner

Expert:  karrs2fix replied 1 year ago.

You may need to see if the parts store will clear the control module memory with a scan tool as sometimes the battery disconnect does not work. Also to answer your first question regarding monitoring the data parameters, most of the generic code readers just display failure code information. You would need to invest a little more to have the ability monitor the data.

Customer: replied 1 year ago.
OK. I will stick with my plan and clean the MAF. The car has 148K miles. Once MAF is cleaned, I will disconnect battery and wait ten minutes. Is this enough to clear the computer?
Customer: replied 1 year ago.
OK. Thanks. Forgot to mention that in addition to the P0174, there is a P0171 code too. They seem to simply record the same problem for Bank 1 and Bank 2 with the same probable causes.
Expert:  karrs2fix replied 1 year ago.

I would leave it disconnected for at least 30 minutes, also when disconnected touch the cable ends together. If that does not work a scan tool will need to be used to reset ECM. With both banks setting lean codes it is most likely the MAF is contributing to the problem.

Customer: replied 1 year ago.
OK. I think we're finished. Thanks.
Expert:  karrs2fix replied 1 year ago.

Your welcome, let me know if you need any further assistance.

Expert:  karrs2fix replied 1 year ago.

did you clean the maf sensor and how is the vehicle doing?