Code po 171
There are two common things that cause this code. The first is a dirty MAF sensor. The sensor is located on the side of the air filter cover. It can be removed and visually checked for dirt/debris. If it is dirty it can be cleaned with MAF sensor cleaner. The second is leaking intake manifold gaskets. The engine will need to be cold and a smoker will be needed to check them. The good news is the parts are cheap and they can be done in less that an hour.
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SOURCE: po171 error code
P0171 means the system is lean on cylinder bank number one, with just the one code you could replace the bank one upstream O2 sensor and that will most likely cure the problem.
SOURCE: I have a check engine light on my 1999 Chev
9 out of 10 times this is due to a dirty MAF sensor. If you run an aftermarket air intake that uses an "oiled" filter - you greatly increase your chances of this. You can purchase "electronics parts cleaner" from an auto parts store and spray it on the MAF sensor (you'll have to remove any intake tubing to get to it) and clean it. BE VERY CAREFUL to not damage the sensor - don't attempt to wipe it off on the inside, you can damage it beyond repair.
Hope this helps and good luck!
-KC GTO Dad
SOURCE: my check engine light came on 2004 ford taurus had
P174 means Oxygen sensor was slow in switching Single, Right
or Rear HO2S - Fuel control
P171 means Oxygen sensor not switching - system was at adaptive
limits - Single, Right or Rear HO2S - Fuel control
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SOURCE: I have a 2001 Lexus gs300 and I need to repair
Buy the sensors and put them on yourself. Buy the aftermarket. They are the same. OEM will cost you about $110 each, Aftermarket $65 each. I work for Bosch and run the line that makes oxygen sensors, there's a lot people don't know about aftermarket and OEM. These can be removed with a 22mm wrench or you buy a special oxygen sensor removal socket/wrench. It's a matter of getting it loose. Run the engine for 1-2 min to warm the exhaust, this helps to loosen the sensors and keeps from stripping the threads. If a shop does this $250-325 depending on shop rates.
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SOURCE: check engine light 2003 BMW 325i
both codes are for lean mixture ... bank one and bank two .....that usually means a vacuum leak in the air intake system ... there is a Y shapped boot off the throttle body that fails frequently .. look for a hole or tear or general deterioration ... there is a second boot after the MAF (mass air flow) sensor, that is another possibility ... any off the vacuum hoses you can see under the fancy cover plate could be leaking .. there is a "crank case breather diaphram" that can do the same ... you can test that by removing the oil filler cap slowly (running) ..there should be a sllight vacuum release ... if its a big vacuum whoosh and maybe engine stumbling then suspect the crank case breather diaphram ... finally you could have a bad MAF sensor but more likely the vacuum leak ... running with a lean mixture can eventually damage valves and valve seats ... i use a small rubber hose to my ear to find vacuum leaks (stethoscope) ...
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