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Old 08-10-09, 01:31 PM   #1
jimbo22s
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Default Error code P0171 - lean bank 1

I received this error and changed the MAF sensor. The CEL and VSC Off light came on again shortly after but has not come on again in the over six months since I unplugged the battery. I have driven the car only three or four thousand miles since and not much on the highway. (The VSC Off light came on one other time about four months ago but has not come on again even though I did not do anything.)

Should I assume that the issue is resolved?

I have the same trip of a few hundred highway miles on which the light came on in the first place and would like to try to make it is resolved beforehand.

Thank you.

1999 ES300
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Old 08-10-09, 04:27 PM   #2
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do you have an aftermarket intake?
i know that with my aftermarket exhasut system i was getting code for the 02 sensor and then i switched to the O2 simulator and upgraded to a high flow filter, in which whenever i drive on the highway and let me car coast (5 spd) in neutral it dies down and once in a while i get a fault code for to lean.

and another suggestion is going to autozone and getting them to use an OBD scanner to check if the code is still there and if they can find any other codes, and delete those
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Old 08-10-09, 07:28 PM   #3
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You need to check for any pending or history codes in the ECU. Anyone with a good scanner should be able to do that for you.
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Old 08-10-09, 07:35 PM   #4
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generally, a single lean bank doesn't point to the mass air flow sensor - it typically points to an intake gasket leak, injector problem, or bad o2 sensor...

but, this is a generalization and definitely not the rule...

as RT said, get a decent scanner and see if there are any pending codes...
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Old 08-10-09, 08:49 PM   #5
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Quote:
Originally Posted by jimbo22s View Post
I received this error and changed the MAF sensor. The CEL and VSC Off light came on again shortly after but has not come on again in the over six months since I unplugged the battery. I have driven the car only three or four thousand miles since and not much on the highway. (The VSC Off light came on one other time about four months ago but has not come on again even though I did not do anything.)

Should I assume that the issue is resolved?

I have the same trip of a few hundred highway miles on which the light came on in the first place and would like to try to make it is resolved beforehand.

Thank you.

1999 ES300
If the code is reading "lean on bank 1 only", I would say it's the air fuel ratio sensor. Bank 1 is the one that faces towards the firewall. But before jumping into conclusions, do check if there are any vacuum leaks, check your intake see if it's leaking, make sure the injectors are ok. I doubt it's the MAF sensor because if it was, you would have poor driveability and it would say lean on both banks not one. After all, I'm leaning towards the Air Fuel ratio sensor. GL.
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Old 08-10-09, 11:09 PM   #6
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Its EXTREMELY common on the ES300's and RX300's to get a P0171 and have it be the MAF. I see it twice a week... just had one today. It just usually registers on Bank 1 first...
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Old 08-11-09, 05:00 PM   #7
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Agree with RT and Mitsu. A good scan tool that can read the freeze frame data. For P0171 you need to look at the total fuel trim(short and long term combined) it should be close to zero. If it's close to zero then your MAF is o.k, now look for the reading of the A/F or O2 sensors. Make sure you check the O2 sensor 2(the one after the cat).
If you see the total fuel trim bank 2 or bank 1 let's say " +34%" that's mean your MAF is bad.
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Old 08-16-09, 08:18 PM   #8
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If the MAF sensor is acting up then it would say both banks not just one.
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