Replaced o2 sensors but still error codes P0171 and P0174 comes up?

Ok error codes P0171 and P0174 are related to faulty bank 1 and bank 2 o2 sensors.Replacing the o2 sensor wioll mostly solve the problem.---------

But as you mentioned in your question, that o2 sensors are already replaced.-------

Then as per that, there are few more possibilities which will cause these error codes.--------

Possible causes are:

- Intake air leaks.
- Injectors.
- Exhaust gas leaks.
- Incorrect fuel pressure.
- Lack of fuel.
- Mass air flow sensor.
- Incorrect PCV hose connection.

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Most possible cause after o2 sensor replaced for this error codes coming back is faulty or dirty MAF sensor.-----

Remove and clean the MAF sensor.Then see if the error is still there.------

If maf sensor is checked ok, then other possibility is low fuel pressure.Get the fuel pressure checked, if its checked low then, problem relates to faulty fuel pump and clogged fuel filter.If the fuel pressure checked ok, then check the fuel injectors, are the injectors leaking or getting clogged, are they dirty and needs any cleaning.-------

If injectors also checks ok, then check the pcv hose.Is it blocked or having vacuum issues.------

You can pull the oil cap or the oil dipstick with the engine running to see if there is engine vacuum in the crankcase.
Pull the dipstick and put your finger on the hole and if you feel a vacum then it's the pcv problem.But if you dont feel vacuum, then its not pcv problem.----------------

But if pcv checked ok, then its very much possible that problem relates to ECM.The new o2 sensors are not getting detected by your cars computer.The computer in the car is thinking that o2 sensors are faulty and still not replaced.----------

The ECM has to be reprogrammed to accept the parameters of the new sensor. First try manual reset, disconnect the negative battery terminal of your cars battery for 30 minutes then reconnect it and check.If the error is still coming up and all other possibilities checked ok, then get the ECM reprogrammed by the dealer.The ECM will start detecting the new o2 sensor.Once it starts detecting the error will not come back again.---------

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