Two codes, PO171 and PO174 - Lexus IS Forum
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post #1 of 10 (permalink) Old 09-10-2005, 06:41 PM Thread Starter
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Two codes, PO171 and PO174

I have searched and couldn't find any info on fuel filters. Does this car not have one? It's my G/F's car. I have an intake on it (generic gauze type filter) it also has a header, high flow no cat midpipe and a low restriction muffler. I also have an O2 simulator on it which is working fine. I have had all this stuff on since January with no problems other than an O2 sensor going bad. I have rechecked everything and nothing is loose or broken under the hood. It has 50,800 miles on it.

I took the air filter off the other day and cleaned/reoiled it and put it back on. I have already checked the maf to make sure it has no oil on it, it's clean. I had the codes read this morining and reset and the CEL came back on this afternoon, like 20 miles. I just can't see both primary O2 sensors going bad at the same time. I am thinking a clogged/dirty fuel filter or injectors. Any thoughts? Any help? Thanks guys.
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post #2 of 10 (permalink) Old 09-10-2005, 10:04 PM
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The following information is from Lexus DTC detecting condition for your codes listed


When DTC P0171 or P0174 is recorded, the actual air-fuel ratio is on the LEAN side. When DTC P0172 or P0175 is recorded, the actual air-fuel ratio is on the RICH side.
If the vehicle runs out of fuel, the air-fuel ratio is LEAN and DTC P0171 or P0174 is recorded. The MIL then comes on.

Lexus list the following areas for inspection

Trouble areas:

Air Induction system
Mass air flow meter
Injector blockage
Fuel Pressure
Coolant temperature sensor
Gas leak on exhaust system
Open or short in heated oxygen sensor (bank 1, 2 sensor 1 circut)
ECM


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post #3 of 10 (permalink) Old 09-11-2005, 07:40 AM Thread Starter
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Thanks. I am going to try some injector cleaner first. I have been driving it around with the restrictor removed from the muffler=more flow so I will put that back too, the g/f doesn't like it so loud. So there is no fuel filter then?
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post #4 of 10 (permalink) Old 09-11-2005, 06:37 PM Thread Starter
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No intake leaks. If the mass air meter was bad then usually the car won't run. I am going to get the fuel pressure checked as soon as I can. Coolant temp, when the car is cold it hesitates and doesn't want to accelerate when starting. There is no exhaust leak. I'm quite positive that both O2 sensors didn't go bad at the same time. ECM doubt it.

The cel comes back on in like 20 miles and seems to when going WOT, which would suggest fuel pressure. Oh well I'll find out eventually.
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post #5 of 10 (permalink) Old 09-12-2005, 06:39 AM
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the mass airflow meter is dirty. giving the computer false readings of how much air is entering the engine. because of this the engine is running lean, and causing these codes. remove, clean and reinstall sensor. reset computer.

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post #6 of 10 (permalink) Old 09-12-2005, 08:28 AM Thread Starter
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I have already removed cleaned/reinstalled the maf sensor and reset the pcm. I may have to replace the sensor. Thanks for the info.
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post #7 of 10 (permalink) Old 09-12-2005, 09:08 PM
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cleaning and reinstalling only works part of the time, if in park or in neutral you put it to the gas to the floor, and it trys to bog down before it revs. it is most likely your maf.
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post #8 of 10 (permalink) Old 09-13-2005, 01:41 PM Thread Starter
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It's at the dealership now, they said they would still warranty it even though it's just over 50K. I'll see what happens later today.
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post #9 of 10 (permalink) Old 09-13-2005, 06:48 PM Thread Starter
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The dealer put a new maf in it, the old one had a small piece missing from it, it still does the same thing. When cold the car won't take throttle, after it warms it runs ok. I am thinking maybe the coolant temp sensor is bad and the car isn't going out of warm up mode or something. I don't know, I have to go out of town tomorrow for a week and a half so maybe I can fix it when I get back.
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post #10 of 10 (permalink) Old 07-19-2008, 10:57 PM
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I have these same codes and car does the same thing. Have you figured out the problem?
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