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p0171 code

Discussion in '1st Gen. Tacomas' started by spider22, Oct 12, 2012.

  1. Oct 12, 2012 at 9:31 AM
    #1
    spider22

    spider22 [OP] New Member

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    Have a 2003 Prerunner. Engine light came on a couple days ago. I took it to auto store to put on computer. The computer read a p0171 trouble code, which is System too Lean (Bank 1). I bought some cleaner to clean the MAF sensor, but engine light stayed on, so I bought a new sensor and replaced it. Light is still on. This whole time my truck is running fine, not sluggish nor missing. Any ideas??

    Spider22
     
  2. Oct 12, 2012 at 2:35 PM
    #2
    Hawaiian05

    Hawaiian05 Well-Known Member

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    Just checking, you did clear the code once you cleaned and /or replaced the sensor, right?
    Did you check for any leaks near/around the intake hose or airbox? I've seen a few in the past in which either a vacuum hose was disconnected or the plastic air tube was loose. I've also seen cracked airboxes, which caused an air leak or a "lean" code. Do a thorough visual check first before you do anything else...
     
  3. Oct 12, 2012 at 9:21 PM
    #3
    BamaToy1997

    BamaToy1997 ASE Master Tech Vendor

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    A p0171 can be stored for a lot more reasons that a dirty/failed MAF sensor. There are several possible issues that you need to address. Vacuum leaks, injector issues, O2 sensor issue, fuel pump issue (less likely since it is only one bank, but the other side could be right on the brink of code) I would get a data reader and check your fuel trim numbers. Are they severe? (+20% or more) or just enough to set a code (Sometimes as low as 7%) Otherwise you will be looking at throwing parts at it. Find the failure. try reading trim data then carefully spray a product like brake clean around the intake manifold and vacuum hoses. If the fuel trim suddenly shoots the other direction (rich) then you have found the area at fault.
     
  4. Oct 15, 2012 at 4:15 PM
    #4
    spider22

    spider22 [OP] New Member

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    Took truck back to get p0171 code cleared, now along with p0171, the computer also got p0113 and p0102 codes. Truck still running smooth. I did try to unplug MAF sensor while truck was running and it killed. So I would think that it is getting correct voltage to it. The other two codes show a possible cause being ECM has failed. What now?

    Spider22
     
  5. Oct 15, 2012 at 4:23 PM
    #5
    isu2014

    isu2014 RAT Products

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  6. Oct 15, 2012 at 4:31 PM
    #6
    98tacoma27

    98tacoma27 :POOPCORN: Staff Member

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    You blew the fuse when you disconnected the MAF with it running.

    http://www.ncttora.com/fsm/2003/Repair_Manual/03tacoma/di/eg5vzfe/cip01001.pdf

    http://www.ncttora.com/fsm/2003/Repair_Manual/03tacoma/di/eg5vzfe/cip01101.pdf
     
  7. Oct 15, 2012 at 6:34 PM
    #7
    Robertgeejr1

    Robertgeejr1 Well-Known Member

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    I have done all the hi-pro mods for a life time, since I got this truck at a great price, I will be happy with showroom new.
    one easy way to clear the codes, is to just disconnect the neg. battery cable and just let her rest for 30 mins to one hour.
    be careful discounting things while the truck is running the last thing you want to do is to cause a backfire or two. that could lead to more problems.
     
  8. Oct 16, 2012 at 5:17 PM
    #8
    spider22

    spider22 [OP] New Member

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    Ok, this is what I did. I checked ECM fuse which I believe is the EFI fuse. It is good.I disconnected negative side of battery to try and clear code. In the process I noticed that the negative lead from the battery to chasis ground was broke. I reattached it and connected battery back. I started engine and check engine light is off. Coincidence??

    Spider
     
  9. Oct 16, 2012 at 5:22 PM
    #9
    98tacoma27

    98tacoma27 :POOPCORN: Staff Member

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  10. Oct 16, 2012 at 6:13 PM
    #10
    Robertgeejr1

    Robertgeejr1 Well-Known Member

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    I know you are going to argue with everything I say, but from everything I have read over many, many years, it is advised to disconnect the neg. cable for 30 mins.
     
  11. Oct 16, 2012 at 7:09 PM
    #11
    isu2014

    isu2014 RAT Products

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    I've only heard this rule in regards to working with airbags. I always used to reset my check engine light by pulling the efi fuse.
     
  12. Oct 17, 2012 at 5:30 AM
    #12
    98tacoma27

    98tacoma27 :POOPCORN: Staff Member

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    X2. I use a reader or the Ultragauge to reset. I only resort to the neg cable when I don't have access to a reader. And when I pull the cable, I wait about a minute to let any capacitors discharge.
     
  13. Oct 17, 2012 at 6:14 PM
    #13
    spider22

    spider22 [OP] New Member

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    Took truck to work today. It ran fine. Check engine light is still off. Thanks for the help.
     
  14. Jun 28, 2014 at 8:35 PM
    #14
    KJW

    KJW Member

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    Just sold a '99 Tacoma with 175,000 miles that would not pass smog due to PO171. Truck runs smooth and gives no indication of vacum leaks. After reading and hearing all sorts of stories I did the following:
    Wasted time and money letting Toyota clean the MAF and get the voltage reading correct according to them. Failed again on PO171. They just said.....Sorry.
    Then I brought it home and did a complete visual on the engine vacum lines and pulled out the air cleaner box to clean and check for cracks.....non found......went to AutoZone bought a new sensor for $80 put everything back together and drove the truck for 30 miles mixed freeway and street.
    Past smog with no problems same afternoon.

    Toyotas seem to get hit hard with this code and you can waste a lot of time chasing it. The above worked for me pretty quickly.

    kjw
     
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