P0174 System Too Lean (Bank 2)

Description and meaning of DTC p0174

This diagnostic trouble code (DTC) is a generic powertrain code, which means that it applies to OBD-II equipped vehicles. Brands of vehicles affected include but are not limited to Ford, Lexus, Chevy, BMW, Toyota, Jaguar, Acura, Volvo, Nissan, etc. Although generic, the specific repair steps may vary depending on make/model/engine. Anecdotally this code seems more common in Ford Chevy vehicles. Every vehicle has a PCM or ECM (powertrain / engine control module). It's basically the "brain" or main computer of the vehicle, it's job is to monitor a variety of sensor readings and use that information to run the engine in the most efficient operation given the current conditions. Basically this P0174 code means that the upstream oxygen sensor in bank 2 reporting a lean condition(too much oxygen in the exhaust). On V6/V8/V10/V12 engines, Bank 2 is the side of the engine that doesn't have cylinder #1. The engine uses what are called O2 or oxygen sensors in the exhaust stream to determine the air to fuel ratio of the exhaust leaving the engine. The PCM (or ECM) uses that information to determine how much fuel to inject via the fuel injectors many times per second. The ideal air:fuel ratio is 14. 7:1. The PCM can adjust the amount of fuel by adding more fuel or taking away fuel to keep the engine operating efficiently and with low emissions. If an O2 sensor is telling the PCM through it's reading that the exhaust has too much air in it, the PCM compensates by adding more fuel. In this case it's adding more fuel to bank 2. The PCM will only adjust up to a certain point to the amount of fuel that it will inject in an attempt to bring that air:fuel ratio as close to optimal as possible. When the PCM has reached it's limit on how much fuel it will inject but the front (upstream) bank 2 oxygen sensor still detects a lean condition, the PCM will continue to command a higher than normal amount of fuel to bank 2 and will trigger this code and illuminate the MIL (malfunction indicator lamp).

p0174 diagnostic trouble code symptoms

You will more than likely not notice any drivability problems as a result of a P0174, although theremay be symptoms such as: lack of powerincreased fuel consumptiondetonation (spark knock)hesitation/surge on acceleration

DTC p0174 - possible causes

A code P0174 may mean that one or more of the following has happened:The MAF (Mass Air Flow) Sensor is dirty or faulty (if equipped). Note: The use of "oiled"air filters can cause the MAF to become contaminated if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the siliconepotting material used to protect the circuitry. There could be a vacuum leak downstream of the MAF sensorFuel problem (rail/injectors/pump/regulator)

How to fix OBD-II diagnostic trouble code p0174

If you find yourself with this code, do not just assume the O2 oxygen sensor is bad and replace it first! Please do proper diagnosis before even buying parts. Proper step-by-step diagnosis will save you money in the long run, and you'll generally learn new things. We can't give vehicle specific repair steps because it can vary depending on the year, make, model, and engine of your particular vehicle. We do, however provide some general diagnostic information that will hopefully help you solve your P0174 lean code. Possible solutions include:In many cases, simply cleaning the MAF sensor does the trick. Consult your service manual for it's location if you need help. I find it'sbest to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it'sdry before reinstallingInspect all vacuum and PCV hoses, replace if necessaryCheck for a dirty fuel filter and proper fuel pressure

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