my expedition is giving me codes P0171 and P0174 which means system too lean on bank1 and bank 2

Amanda Page

Asked by Feb 04, 2015 at 09:34 PM about the 1998 Ford Expedition 4 Dr XLT SUV

Question type: Maintenance & Repair

I actually had 3 codes when i took to shop they replaced intake gaskets done coolant
flush and replaced # 2 sparkplug cause it was cracked do from leak of intake gasket and
that was the 3rd code i mentioned P0302 and it fixed the feel of it driving well today i
turned my defrost/heat on and smelt antifreeze and my front heat blows cold air but rear
heat works wonderful please any suggestions

2 Answers


First replace the fuel filter, then run a fuel system pressure test, if the pressure tests good then clear the codes and verify they cleared, then road test, if the check engine light comes back on with the same codes you may have partially plugged injectors or you still have an internal vacuum leak. Coolant smell from the heater is almost always a leaking heater core, on this rig it is not cheap to replace, the part price is not bad but the labor is the killer.

2 out of 2 people think this is helpful.
Martin Kamenar

PO171 And PO174 means it's running lean. This means your manifold air pressure sensor is saying X amount of air entering motor yet your O2 sensor is saying XY amount of air is exiting engine. The computer reads this as extra air is getting in somewhere. This is usually a vacuum leak from your PCV vacuum lines. Start your engine, let it idle. Spray starting fluid around your PCV valve and all vacuum lines connected to it. You should hear you idle pick up. Then trace those lines with your finger and you will find a hole that rotted through. go to the following links for more help and videos. and

5 out of 5 people think this is helpful.

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