2005 Ford Escape



April, 5, 2009 AT 8:23 AM

Engine Performance problem
2005 Ford Escape 6 cyl Front Wheel Drive Automatic 135000 miles

Dear sirs--

I own a diag tool that is reading P1131, P1151, P0171, P0174. The 31 and 51 codes indicate " lack of Ho2s11 and Ho2s21 switches-sensor indicates lean", according to my diags.

I have changed both bank 1 and bank 2 upstream sensors, and I have changed the MAF.

The car will not idle properly. It will surge when first started and when sitting at a red light.

I clear the codes but continually get lean mixtures turning the check engine light back on.

Where I should look next?


1 Answer



April, 5, 2009 AT 8:32 AM

P0171and p0174
Vacuum Leaks/Unmetered Air

With this condition, the engine will run lean of stoichiometry (14.7: 1 air/fuel ratio) if the PCM is not able to compensate enough to correct for the condition. This condition is caused by unmetered air entering the engine, or due to a MAF malfunction. In this situation, the volume of air entering the engine is actually greater than what the MAF sensor is indicating to the PCM. Vacuum leaks will normally be most apparent when high manifold vacuum is present (for example, during idle or light throttle). If freeze frame data indicates that the fault occurred at idle, a check for vacuum leaks/unmetered air is the best starting point.
Examples: Loose, leaking, or disconnected vacuum lines, intake manifold gaskets, or O-rings, throttle body gaskets, brake booster, air inlet tube, stuck/frozen/aftermarket PCV valve, unseated engine oil dipstick.

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