2002 windstar 3.8L, Is p0171 upstream on bank 1, and is p0174 downstream on bank 2.

P1151 Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 2


p1131 p1151 p0171 p0174 p1131 p1151 p0171 p0174
All of these p1131 p1151 p0171 p0174 codes indicate a problem with a lean condition. This engine is known for vacuum leaks, so before you start throwing oxygen sensors at the problem, it pays to perform some diagnostics.
Start by cleaning the MAF sensor. Spray the sensor with CRC MAF sensor cleaner. Next, check the plastic vacuum lines, especially where they meet with rubber boots. If they are cracked or the rubber is swollen, replace the line. Then check the rubber elbow that holds the PCV valve. That elbow is a know failure point. In fact, the entire PCV tubing is a trouble spot on these engines. (thanks Ford).
After you've checked for vacuum leaks, check the operation of the oxygen sensors. The easiest way to do that is to disconnect the sensor from the harness. Connect one lead of your digital voltmeter to the black wire on the sensor and the other lead to battery negative. Then start the engine and add fuel (either propane, starting fluid, or carb cleaner) into the throttle body to force the mixture to rich. You should see a corresponding increase in voltage as you add fuel (from 0 volts to slightly less than 1 volt). Start and stop the fuel enrichment and watch the meter to see if the volts drop as you stop adding fuel. If you see no change, the sensor is dead. Replace it.
You can also use the fuel enrichment procedure to locate intake gasket leaks.
P1131 Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 1
P1151P1151 Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 2
P0174 system lean bank 2
P0171 system lean bank 1


This is the only info that didn't come back directly to FORD (yet still mentions it) instead of GM. Not to sure you got the correct code.

Don't even bother cleaning them, it may work sometimes but not very often and can even make it worse by cleaning and putting back. The upper is where I would start, since the second is reliant on the first to get its readings. But I do believe that is the next one in line on those, it's been a while since I've seen one. But yeah get a new sensor and clean throttle body. Take body off if you can to clean it. Just more junk to go down the line depending on the condition and buildup. But you can get a much better job this way

P0171 system too lean bank 1
P0174 system too lean bank 2
links to information on the codes

it means that the O2 sensors in your vehicle detected a lean condition in their respective banks. this could be caused by a dirty MAF (mass air flow) sensor or a vacuum leak downstream from the MAF sensor

sometimes you can clean the MAF with electronics cleaner or brake cleaner but be sure to take it off the vehicle first. be careful not to damage the MAF while spraying the cleaner, and allow it to dry completely before installing it on the vehicle.

fault code P0171 System Too Lean (Bank 1), this fault could be occurred because of faulty upstream or downstream oxygen sensor of bank one you must check the actual value of upstream and downstream oxygen sensors, if the oxygen sensor values are same both side bank one and two check subpressures for spark plugs (spark plugs wires ) and spark plugs and ignition coils, can do one thing to find out easily, swap spark plugs subpressures and ignition coil between both banks after that clear code and start if the code change to P0174 System Too Lean (Bank 2) you can understand that's the fault create by one spark plug or wire or coil then swap one by one and you be able to find which one is the faulty one replace it.is this information helped you?

are the codes p0171 and p0174? p0171 system too lean (bank #1) p0174 system to low ( bank # 2) o2 sensors will go in pairs.

i have a feeling the problem is not the sensors, they are reading lean indicates that air is getting into the engine around monitored system, basically a vacuum leak, which causes surging, also get a real time engine monitor not just a code scanner, some even have snapshot capabilities that will freeze the readings when something abnormal happens, just don't go replacing parts without knowing why

1998 Ford Truck Windstar 3.8L SFI 6cyl, there are 4 oxygen sensors on the Windstars They are divided into 2 banks of 2. Bank 1 is the for the rear 3 cylinders of the engine - Bank 2 is for the front 3 cylinders. Bank 1 / Sensor 1 (upstream) is located just below, in the pipe, the exhaust manifold on the back of the engine.

REMOVE TIP: you may have to bend part of the transmission heat shield out of the way - be sure to put it back when done.
Bank 1 Sensor 2 (downstream) is located just past the drivers side catalytic converter.
Bank 2 Sensor 1 (upstream) is located just below the exhaust manifold, in the pipe, at the front of the van - access is from the top.
Bank 2 Sensor 2 (downstream) sensor is located just past the passenger side catalytic converter.

NOTES: * Use lots of penetrating oil - allow to soak - to make removal easier and avoid damaging the exhaust pipe

Hope this help; TY for using Fixya (remember rated and comment this).

P0137 o2 circuit low voltage bank 1 sensor 2 --o2 sensor after the cat converter -check for faulty o2 sensor -short or open circuit exhaust leak near sensor or plugged cat converter ----P0171 and P0174 -system too lean bank 1--and system too lean bank 2 they are usually from the same problem which can be caused from the o2 problem but check ur maf sensor connections and or clean if necessary[carb cleaner] vacuum leak downstream from maf sensor also inspect pcv lines

P0171 indicates a lean condition. The most common cause of this is a defective mass air flow sensor. Also check if any vacuum leaks. P0174 OBD-II Trouble Code

Technical Description

System Too Lean (Bank 2)

What does that mean?

Basically this means that an oxygen sensor in bank 2 detected a lean condition (too much oxygen in the exhaust.

Note: This DTC is very similar to P0171, and in fact your vehicle may show both codes at the same time.

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Thanks.

p0171 indicates the system is running lean on bank 1,p0174 means the system is running to lean on bank 2 p1507 is an idle speed under run fault i'd suspect an air leak is the cause of your problem check air intake system for airleaks