Fault code P0171 - please help with my detective work!

Discussion in 'K11 General Discussion' started by Lynxy, Nov 27, 2011.

  1. Lynxy

    Lynxy New Member

    Hi everyone,
    I have developed a P0171 fault (system lean bank 1) with symptoms very similar to a problem outlined by Dave100 in posts #1, #6 and #9 in this forum thread http://www.micra.org.uk/threads/11571-Bosch-Micra-throttle-body?highlight=P0171 which was started way back in 2006 but seems very similar to my problem, but has left me wondering because of a few differences in the circumstances – so I need some help in my detective work!

    I think I should give a little background info before I launch into describing the exact details leading up to the fault. My Micra Vibe 1.0 petrol is a K11C on an 02 plate, i.e. the second facelift.

    Thanks to help from Frank and other forum members here, I solved a P001 fault back in the summer (2011) with a brand new replacement MAF sensor which cured the problem and saved me 100s of £££s. Also, thanks to advice I found in previous posts by Fordy, I don’t have the NGK BKR5E spark plugs fitted and had Bosch plugs fitted at my last service which was at virtually the same time as I replaced the MAF sensor. I mention these replacements because Fordy has mentioned them previously as possible culprits behind the P0171 fault in Dave100’s thread I mention above (in post #5). I did notice too that Dave said he had changed the Lambda sensor but the fault still kept appearing.

    About two weeks ago I had an oil sump replacement which, I have learned, involves removing part of the front exhaust. About a week after the oil sump replacement, the check engine light came on with fault P0171. After I erased the code the same P0171 fault has appeared again, but only after several days following various low and higher speed runs adding up to 100-150 miles – and both times the light has come on during a higher speed run (i.e. 70 mph on a dual carriageway) and neither time during the slower around-town runs. In this sense it does not resemble what happened with my previous P0100 fault when the light would reappear instantly after just a few revs following erasure of the code (and was solved by the new MAF sensor).

    I understand from the thread I mentioned above that code P0171 could be the MAF sensor at fault again – albeit far more intermittently this time, as I described above. But I am not sure if my MAF sensor might be to blame for the P0171 fault because the MAF sensor is so new, and its location in the engine bay further means it couldn’t have been damaged during a replacement to the oil sump. I realise of course that an oil sump replacement and a faulty MAF sensor could be a complete coincidence with the P0171 fault, but it seems such a big coincidence that even I have questioned it - and I am certainly not a mechanic!

    Is it possible that during the oil sump replacement that a sensor was damaged near the exhaust front downpipe which, according to the Haynes manual, the mechanic would have had to remove to get to the sump? I am not sure where the Lambda or 02 sensors are located – would I be right I saying these are two separate sensors? The Haynes manual mentions an ‘exhaust gas sensor’ and how delicate it is (which is what aroused my suspicions about this sensor being damaged instead of the MAF) – but by ‘exhaust gas sensor’ do they mean the 02 sensor? Could this sensor be the one that needs replacing? I have also read on other forums that fault code P0171 could be vacuum hoses or injectors although advice given in the 2006 thread suggests to me that these are less likely explanations.

    I apologise for the length of this post, but I wanted to be as clear as I could from the off. Thanks too in advance to everyone who replies. (Y)

    Lynxy
  2. Lynxy

    Lynxy New Member

    PS - this isn't related directly to the thread here, but I still haven't worked out how to do the special 'Thanks' to forum members - please can anyone demystify this for me? lol
  3. frank

    frank Club Member

    yes your coilpack engine should have 2 lambda,s lynxy (pre and post cat)
    and i,ve seen a few posts about a faulty 2nd one before, any info on the ilexa forum ?

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