I am getting an engine fault light in my Vauxhall Corsa 2011 with fault code

P0171 "System too lean"

This is not constantly on and only comes on intermittently. This caused a problem when taking it to my local garage because they could not diagnose the fault as the light had gone off. The light came back on after an hour or so of driving.

Does anyone know what this issue could be? There are a number of possible reasons listed online but I didn't notice anyone saying it comes on intermittently so this may be a clue.

  • 1
    What engine is in the car? Commented Mar 5, 2019 at 11:54
  • 1.2i 16v 1229 cc petrol engine
    – AWGIS
    Commented Mar 5, 2019 at 13:09

2 Answers 2


Ugh.. Corsa-Ds seem to throw this code for everything, sometimes just because the day ends in a "Y"

A failing Manifold Absolute Pressure (MAP) sensor is the usual culprit - particularly with the intermittent nature. If the MAP is failing you'll see the code when accelerating hard or the engine is under load (which means when it's just sat there at the garage it's all sweetness and light).

The EVAP canister or the PCV breather are some of the other usual suspects but typically if they have gone you'll get the code all the time.

  • thanks - is there a go to method to test if it is the MAP?
    – AWGIS
    Commented Mar 5, 2019 at 15:31
  • @AWGIS Possibly - Does your scanner do live data? Commented Mar 5, 2019 at 15:44
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    First test it at idle (you should see a relatively low voltage ~ 0.3V), then go rapidly to wide-open throttle and a few seconds later drop quickly back to idle. You should see it go to ~4.9V at WOT and it should cleanly return to the original idle value. Then take it out and (where safe and legal to do so) do a high-load, steady throttle run (up a steady straight incline is ideal, perhaps in one gear higher than you would "normally" drive it) and look at the logs - if you see erratic voltages during your run then that's a borked MAP Commented Mar 5, 2019 at 16:44
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    @AWGIS Possibly - I'm often dubious of cleaning them as you can end up doing more harm than good if you aren't careful. Commented Mar 5, 2019 at 16:45
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    @AWGIS it's fairly easy to get it to though, so it's worth checking to see if there's any obvious signs of dirt build up or damage to the vacuum hose. IIRC it's bolted onto the inlet manifold with a single Torx bolt. Commented Mar 5, 2019 at 16:53

Check for vacuum leaks on the air induction system, mass air flow sensor and fuel pump

  • test for ground, 5 volt reference from the ECM and the sensor out put of 0.3-2.0v at idling and then 4.5-4.9v at full throttle opening Commented Mar 5, 2019 at 21:25

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