P0171 code intends to show lean fuel mix status when observed with a bit much presence of 02 molecules inside your exhaust system. These are reflected by the 02 molecules sensing probe element installed in the exhaust manifolds which signals the problem. This is also similar to P0174 fault code problems. This error code could be induced by contaminated mass sensor wiring element fouled by soaking of dirty oil inside the air cleaner. Servicing your mass sensing element component and installing new air cleaner will remedy this code. Whenever the fuel filter hasn’t been replaced for a long time, this is the best time to do it.

To confirm this P0171 fault, be sure you’ve the following symptoms prior to executing repairs: Hesitation, losing of power, pre-ignition and occasionally erratic rpm. If doing the remedies recommended above, the fault stays, try these:

• Evaluate the 02 molecules sensor voltage and check if the voltage oscillates when warmed up. Reading should fluctuates between 0.1 volt to 0.9 volt. Whenever out of this setting, substitute another oxygen sensor.

• measure the mass sensor signal volt reading between idle and high idle speed. If the voltage stays as is, replace the mass sensor.

NOTES:

P0171 on Taurus vehicles:

When accompanied by misfiring, this code is usually cause by defective injector driver. This can be checked by using a labscope testing available from most independent garages.

P0171 on Explorer vehicles:

This code is normally caused by a defective intake manifold gasket leaks best verified using a smoke machine (check your local garages for testing the vacuum leak using the smoke machine).

P0171 on GM Pick Ups:

When triggered, find this code by testing vacuum leaks on the intake hoses and gaskets in the intake manifold. Sometimes, leaks could be found on the vacuum tubing which can crack.

P0171 on Plymouth compact cars:

Check fuel pressure after verifying the vacuum leak. If fuel pressure is weak, this code can appear. Solved by changing the fuel pump.

P0171 on Toyota 4Runner:

Most of this code is fixed by servicing the mass sensor which is done thru cleaning the wire elements of the sensor.

To check P0171 code, it is understood that the engine has been checked for vacuum leak before doing these repairs. Also, check vacuum hoses for cracks and vacuum reading if possible. For assistance, contact ATS.

Thanks!