P0171 and P0135

[nycnftm]

Check engine light on and got codes P0171 and P0135 from Autozone. The piece of paper they give you with the codes lists a bunch of possible things to replace.

I was told by a friend to replace the oxygen sensor. Can you guys please tell me what to buy and replace?

 

[Bedrck47]

When you went to Autozone and had the codes read they had to enter certain information into the scanner in order to get the correct codes for your expy. Like Make Model Year Engine etc. Since we already know its a Ford Expedition it would be nice to know the rest of the information. Also how many miles on the expy.

Before just replacing the O2 sensor being those codes indicate a fuel related problem I would check the fuel system and also check the vacuum system as vacuum leaks could also cause those codes to appear.

When was the last time plugs were changed??
Fuel filter changed?

 

[nycnftm]

It has 155,000 miles it is a 1997 5.4 eddie bauer. I just got it and do not know any history.

 

[Bedrck47]

If it were me I would not just go replacing O2 Sensors without first checking other items You could replace just the sensor and then find out you still have a problem.

Take a can of carb spray and with the engine running spray around the vacuum hoses. pay attention to the hose behind the throttle body and the PCV valve if you have any leaks you will hear and increase in RPM's Also would advise changing fuel filter and plugs

DTC P0171.
For lean and rich DTCs:
Fuel system
Excessive fuel pressure.
Leaking/contaminated fuel injectors.
Leaking fuel pressure regulator.
Low fuel pressure or running out of fuel.
Vapor recovery system.
Induction system:
Air leaks after the MAF.
Vacuum Leaks.
PCV system.
Improperly seated engine oil dipstick.
EGR system:
Leaking gasket.
Stuck EGR valve.
Leaking diaphragm or EVR.
Base Engine:
Oil overfill.
Cam timing.
Cylinder compression.
Exhaust leaks before or near the HO2Ss.

 

[Bedrck47]

Change plugs and fuel filter
clean MAF sensor

Being you have no idea as to the history I would start with the basic maintenance items. And also check for Vacuum leaks. Then clear the Codes and see if any return