P0171 and P0174 codes

My check engine light came on for bank 1 and 2 upstream o2 sensors. I smell raw fuel from engine compartment, and my fuel tank crushed itself causing a hole in the tank. All this occurred after I replacement my fuel cap when the light came on for faulty cap. I've read the vapor canister purge solenoid is the culprit. Is there any truth to that?
Experienced mechanics share their insights in answering this question :
For one, these codes are for a lean condition and are not O2 sensor specific codes. It is true that some of the newer Fords have an issue with the purge valve staying on, putting a vacuum on the system that causes the gas tank to collapse. In fact, there is even a technical service bulletin (TSB) regarding this issue, but it does not apply to your vehicle. One thing I would look at first, is the mass air flow (MAF) sensor. There is a TSB 98-23-03 regarding the codes you have setting as a result of a faulty MAF. Of course, Code P0171 and P0174 can be set by anything that causes a lean condition; from a vacuum leak to a faulty fuel pump. To know for certain, I suggest you have a professional, such as one from YourMechanic, diagnose and repair your vehicle firsthand (https://www.yourmechanic.com/services/check-engine-light-is-on-inspection).

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What Does P0171 and P0174 Mean? DTCs P0171 and P0174 are generic codes that set when the feedback on the engine`s air/fuel mixture becomes too lean for the Engine Control Module (ECM) to correct within its normal operating range. A lean mixture is a mixture that has too much air or not enough fuel.
P0171 is triggered by the engine bank 1 “upstream” oxygen sensor and P0174 is triggered by the engine bank 2 “upstream” oxygen sensor. The oxygen sensor alerts your system when the condition is too lean meaning there`s too much oxygen in the exhaust.
Too much fuel and/or too little air results in the engine running rich setting a P0172 trouble code, while too little fuel and/or too much air results in the engine running lean resulting in a check engine light for the Ford P0171 code.
A P0171 code is set by your vehicle`s powertrain control module (PCM) when it detects that the air-to-fuel ratio of your vehicle is too lean. This means that the PCM is relaying that the engine is receiving too much air into the combustion chamber and not enough fuel.
Can a dirty air filter cause a P0171 code? If your car`s air filter becomes blocked or extremely unclean, it will hinder or restrict the flow of air. This, in turn, results in a lean running state. A dirty or defective MAF sensor, or a clogged fuel filter, can all be responsible for the P0171 code.
You probably know that the answer the questions is — no! A P0171 or P0174 lean code with an O2 sensor reading lean all the time mean — well, several things. The real problem may not be a bad O2 sensor, but possibly be an engine vacuum leak, low fuel pressure or dirty fuel injectors that are causing the engine run lean.
Can a bad fuel filter cause P0174? Yes. The code activates if your car has a clogged fuel filter or damaged fuel pump.
Can bad spark plugs cause p0171? Not likely. A P0171 ( too lean, Bank 1 ) code is most often caused by a vacuum leak downstream from the MAF sensor or a malfunctioning MAF sensor. Bad spark plugs could actually cause the opposite code ( too rich, bank 1).
When the ECM/PCM is having to add too much fuel based on input from the O2 sensor, the fault code P0171 will be sent to the ECM, which will trigger the check engine light to illuminate. This code could either mean that the oxygen sensor is detecting too much oxygen or too little fuel in the mixture.
Code P0174 indicates that there is a lean condition detected by the Engine Control Module (ECM). A lean condition will be created if there is too much air, and not enough fuel, in the air fuel ratio (AFR).
The reading is too lean (i.e. too much air or not enough fuel). P0171 is a bank one reading lean, P0172 is for bank two reading lean. If the PCM is saying is that the sensor cannot be sense, that would be a different code.
Code P0174 indicates that there is a lean condition detected by the Engine Control Module (ECM). A lean condition will be created if there is too much air, and not enough fuel, in the air fuel ratio (AFR).
What the P0171 code means. The P0171 OBD-II code means that, on the first bank of the engine, the fuel system is running weak or a vacuum leak exists near this side of the engine. A lean condition occurs when the engine either receives too little fuel or too much air.

Relevant Questions and Answers :

the most relevant questions and answers related to your specific issue

I have codes P0151, P0171, and P0174. I have changed out my O2 sensor, but now I have all these codes
ANSWER : Hey there. The codes you have downloaded simply relate to malfunctions in the "engine management system." It appears codes were set for oxygen sensor voltage out-of-range, possible EGR (exhaust gas recirculation) problems such as a blockage, and a generic code indicating that the air/fuel ratio is too lean. Codes only give clues. Codes are never to be read conclusively as exactly which part or parts should be replaced until the fault has been inspected.

For example, with regard to the oxygen sensor "code", an exhaust leak ahead of the sensor could cause that code to be set, not to mention a faulty oxygen sensor harness connector. So you could have a perfectly good oxygen sensor reporting the "wrong" data because of a leak in the exhaust that admits unexpected additional air that the sensor "reads".

A key point is that any part referred to in a code has to be separately and carefully diagnosed to determine if the part has actually failed as opposed to a circumstance where the part (often a sensor) is just simply reporting correct data because SOMETHING ELSE has failed. This is why most expert mechanics suggest conducting Check Engine Light diagnostics on codes before moving forward with repair.

In your circumstance, the operating lean codes could possibly be caused by an air leak after the mass air flow (MAF) sensor, such as a torn intake boot, or bad intake manifold gaskets, a dirty or faulty mass air flow sensor, a continuing problem in the oxygen sensor circuit (wiring, exhaust leak), incorrect fuel pressure (or a failing fuel pump), leaking positive crankcase ventilation (PCV) valve, clogged exhaust gas recirculation (EGR) Port, and/or leaking brake booster.

Basically, all of these items, and possibly additional ones have to be checked, and each ruled in or out, in turn, until the root cause(s) are found. If you would like to have all of these codes properly diagnosed, a certified professional from YourMechanic can come to your car’s location to inspect the car.

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only had code P0171 then I went back and this time I also got a code P0068 throttle body along with the P0171
ANSWER : Hi there. Those codes may or may not be related. Proper diagnostic processes will determine the root cause of the failures. When the ECM detects a fault it stores codes. It does not know why or what caused the fault, only that the fault is present. You can always try to clean the parts you mentioned, but it would literally be a blind guess and most likely not a proper repair. I suggest having a qualified technician perform an inspection to avoid replacing unnecessary parts. Your Mechanic has several available technicians that can assist you with a check engine light inspection.

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I got my car check out and the codes come up was P0171,P0431,and P0174. How much will all this will be so I can start driving my c
ANSWER : Codes P0171 and P0174 indicate the engine control unit is detecting the engine is running too lean – too much air and not enough fuel. P0431 indicates the catalytic converter is not operating at peak efficiency – not cleaning up the exhaust emissions properly. Odds are they are all related. Possible causes can be as simple as the wrong gas. This vehicle is not set up to run fuels like E85 and the likes, or "Flex-Fuel" capable as some vehicles are. Be sure that the gas you are using is not one of these "E" flex fuels. Other possible causes can be a vacuum leak. If the air intake tube is cracked/broken, or if a vacuum hose is disconnected or broken, the engine can draw in too much air, which will effect the air/fuel mixture. Odds are if there is a vacuum leak, the engine may have a higher idle. Other components like the mass airflow sensor, coolant temperature sensor, or oxygen sensor can be at fault. The mass airflow sensor tells the engine control unit how much air is being drawn in by the engine and uses this information to adjust air/fuel mixture, ignition timing,etc. The ecu relies on the oxygen sensor to detect how much unburned air and fuel are in the exhaust system and relies on the coolant temperature sensor to detect the engine temperature. As with the mass airflow sensor, the engine control unit relies on these sensors for input to adjust air/fuel mixture and ignition timing. A fault in any of these components can set those fault codes.
Have a certified technician properly diagnose the fault codes to determine the exact cause. Since any of several components can be the cause, it would get expensive to replace parts at random.

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I have a Code P0601 on the PCM. I replaced the PCM, and now I have a code P0118, code P0123, and code P0193.
ANSWER : Hi there, the short answer to your question is no . A PCM with a P0601 (which is a memory module error in the PCM) cannot reliably retrieve codes for the codes you list (P0118 – coolant temp sensor, P0123 – throttle position sensor, P0193 – fuel rail pressure sensor.

Most likely, the P0601 prevents the PCM from getting any codes from the engine sensors. The memory module error may cause in data corruption for collected sensor values, lose of data over multiple sampling periods, or failure of the data collection to work at all. Replacing the PCM was a necessary expense.

If you need assistance with the "new" codes, I would recommend having a Check Engine Light inspection completed by a mobile, professional mechanic, such as one from YourMechanic, to diagnose the new error codes and get an accurate assessment of the repairs needed.

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Error code P0171 and P0174
ANSWER : The high positive long term fuel trim suggests a vacuum leak and/or inadequate fuel delivery. But there are other causes that have to be evaluated as well: bad oxygen sensor(s); dirty MAF sensor; stuck open EGR valve; weak fuel pump; restricted fuel filter; leaky fuel pressure regulator; dirty fuel injectors; and exhaust restrictions such as a clogged catalytic converter. In addition on Ford models, a well known issue is that P0171 and P0174 lean codes can occur if the EGR differential pressure sensor goes bad. After 6 years or 60,000, that sensor is reported to have a high failure rate. If you desire that your vehicle’s lean operating condition be diagnosed and corrected YourMechanic can dispatch a certified Mechanic to your home or office and perform a mobile diagnostic and repair. Please let us know if you have additional questions or concerns.

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My truck is giving codes P0171 & P0174
ANSWER : Hi there. If the engine is running lean, then there could be a plugged fuel filter or a faulty fuel pump with loss of pressure. If the pressure is dropping after 20 to 25 minutes, then there could be a problem with the fuel pump check valve. When the pressure is at 0, having a pressure gauge on the fuel rail, check for the pressure to increase as the fuel pump is turned on when the key is turned on.

If the pressure takes some time before it stops, then the check valve in the pump is sticking open. This means the fuel pump should be replaced. If the fuel pressure is measured very quickly, then replace the fuel pressure regulator on the fuel rail. If you need further assistance troubleshooting your vehicle, then seek out a certified technician, such as one from YourMechanic, who can come to your location to determine why the engine is running at a lean condition and suggest the necessary repairs.

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Error codes P0171 and P0374
ANSWER : Hello. These issues can be caused by a few things. From the codes it sounds like there may be an issue with the fuel system. It may also be an issue with the air intake system allowing too much air into the engine. The main code here is the lean code meaning too much air or too little fuel. I usually start by checking the fuel trim reading are in the computer to see what is going on. This would tell me if I am looking at a fuel system problem or possibly a sensor that is reading wrong. If these codes are present, the computer can also put the vehicle into limp mode which would explain why it is shifting like this. If you want to have these engine codes scoped, consider YourMechanic, as a certified technician can come to you to diagnose the Check Engine Light and pinpoint the underlying repairs that are needed.

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my car is slow to accelerate. i have a p0171 code. i replaced my o2 sensor but the code came back on. what else could it be?
ANSWER : The code P0171 is a lean code indicating the O2 sensor is detecting the engine is running lean – that is, the air/fuel mixture is imbalanced. You may have a clogged fuel filter or a fuel pump that is not supplying enough fuel pressure. You will need to have the fuel pressure and volume checked with a fuel pressure gauge. You can try to replace the fuel filter to see if it helps first. Your best thing to do is to have a mechanic diagnose the problem and check the fuel pressures and filter. Also make sure your air filter is clean and the inlet air tube is not cracked or loose.

Check these items, and if you still need assistance, contact a professional mechanic. A certified mobile mechanic from YourMechanic can visit your home or office to inspect your vehicle’s acceleration issues.

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