Fault codes - fiesta man
I have used an OBDII fault reader on my car and found the following fault:

P0171 System too Lean (Bank 1)

Whilst I understand what running too lean means, I was wondering what would give rise to such a fault being logged.


Fault codes - Andrew Moorey (Tune-Up)
Basically the PCM is looking at the signal from the O2 sensor and seeing a persistent "go rich" signal i.e low voltage despite it richening the mixture. A faulty O2 (HEGO) sensor will give this fault as will a severe air leak in the exhaust manifold or low fuel pressure.
Either check the output voltage from the sensor or if you can get the OBD11 tool to do it look at the 'components' facility and check the sensor there. I think you will find it stuck at about 0.2-0.3v
A classic fault on these is the failure of the fuse supplying power to the HEGO sensor heater coil meaning that the sensor has to rely on the heat of the exhaust gas to get it to working temp instead of its own heater.
Hope this helps

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Fault codes - DL
On what car are you using this code tool?

"Bank 1" suggests a V6 configuration...........
Fault codes - Andrew Moorey (Tune-Up)
On the Fiesta and most 4 cyl you will only find Bank 1, Bank 2,3,4 come in as you rightly say for Vee engines. As the OBD11 and EOBD protocols have to deal with all configurations of engines they use a set system of fault codes.
Hope that makes sense!

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