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Thread: P0171, P01270, P0131 and P0740 Error Codes

  1. #1
    Join Date
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    P0171, P01270, P0131 and P0740 Error Codes

    Last week, I was getting the P0171 and P01270 error codes and torque converter was making a whirling noise, so I replaced the MAF sensor (bosch) on Bank 1 and both OSV/PCV on Bank 1 and bank 2, replaced the trans fluid and filter. Clear the codes and drove the car for 30+ miles and looks goods, no service engine light and no more whirling noise on TC.

    Today, I drove the car for 10+ miles the service engine light comes ON again with the following codes;
    P0171 is back, P0131 (O2 sensor circuit low voltage (bank1 sensor 1) and P0740 (Torque converter clutch circuit).
    NO whirling noise from TC.
    P1270 went away.

    Should I replace both maf sensor (bank1 and bank 2) to fix P0171?
    I also restarted the car after sitting for 30 minutes, P0740 went away. I will drive the car later and see if p0740 comes back.

    I need help on where and what troubleshooting steps to fix the error codes.



    thanks,
    Last edited by tintin91; 07-16-2018 at 08:19 PM.

  2. #2
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    Code P0171-system too lean bank1- means that the computer has noticed (by reading the oxygen sensors) that there is too much air going into bank 1.
    I would attempt to clean the bank1 MAF sensor with only CRC MAF Cleaner.
    Check for intake leaks on bank1 by removing rubber intake boot and inspecting for cracks.
    The codes you posted can be interrelated, so let's see what results we get from this.

  3. #3
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    Quote Originally Posted by MIKYZZ4 View Post
    Code P0171-system too lean bank1- means that the computer has noticed (by reading the oxygen sensors) that there is too much air going into bank 1.
    I would attempt to clean the bank1 MAF sensor with only CRC MAF Cleaner.
    Check for intake leaks on bank1 by removing rubber intake boot and inspecting for cracks.
    The codes you posted can be interrelated, so let's see what results we get from this.

    Bank 1 maf sensor is new part (bosch), no cracks on the intake rubber boot.
    Someone on the forum suggested replacing both maf sensor due to the reading will be out of balance if you replace just one.

  4. #4
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    Having to replace both MAF is nonsense.

    That code indicates unmetered air infiltration,
    so there is a leak somewhere, you may need a smoke test to find it.

    You can try swapping MAF to opposite banks to verify.

  5. #5
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    Quote Originally Posted by MIKYZZ4 View Post
    Having to replace both MAF is nonsense.

    That code indicates unmetered air infiltration,
    so there is a leak somewhere, you may need a smoke test to find it.

    You can try swapping MAF to opposite banks to verify.

    ok, i will try swap the MAF, if the code p171 return will do the smoke test.
    What are the procedure to do the smoke test?
    Last edited by tintin91; 07-17-2018 at 02:20 AM.

  6. #6
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    You can use diagnostics to check whether the MAF is at fault or you have inlet manifold leaks - the only difference between doing this on a 750i compared to the 740i is you have two independent live data screens....

    https://www.meeknet.co.uk/E38/Diagnostics.htm

    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  7. #7
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    Thank you Timm, very informative!

  8. #8
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    MIKYZZ4, was Timm’s comments same as the smoke test you suggested?
    Last edited by tintin91; 07-17-2018 at 05:41 PM.

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