P0174 is a lean mixture code indicated by the presence of too much oxygen in your combustion gases. This code is similar to P0171 except it occurs in cylinder bank 2 opposite engine bank 1 for the Po171 code. The common symptoms of P0174 are lack of power, occasional pinging or detonation. On some occasion, the engine could be running a little bit hot accompanied by hesitation or even surging.

The P0174 can be fixed quickly by servicing your mass air flow sensor. This sensor has a wiring elements which monitors the air flow volume after the air comes from the air filter. This same wire element can be easily corrupted if the air filter is dirty and soaked with oil. If the air filter is not service regularly, the mass sensor element can be buggered up by dirt giving a false readings or signals to your engine computer.

P0174 tip for mass sensor:

Whenever you service your mass sensor, reset the computer P0174 fault code by disconnecting your battery connections for 1 minute and reconnect. When you take it for a road test and see only a slight improvement, replace the mass sensor. Always use the mass sensor recommended by the vehicle maker to avoid further complications. This is the only sure way the P0174 code will not return.

Other causes of P0174 code:

Vacuum leak:

P0174 code can be triggered by the presence of vacuum leak in your engine. You can check this by checking the vacuum hoses and the top engine intake gaskets. To test, first do it visually and using a lot of listening. When you put your ear closer to a running engine at idle, chances are you will hear a hissing sound if the vacuum leak is bad. Wiggling the vacuum hoses and spraying mist of water on suspected leaky hoses and gaskets can change the engine rpm when the water penetrate the vacuum leak. You can also look for oily engine top component like your pcvs and signs of wetness which indicates an oil leak when the engine is stopped. Shaking or cleaning the contaminated part might lead you to a blocked PCV valve which could alter the engine vacuum operation.

Surging:

P0174 can be easily detected when your engine is idling abnormally high. Its because the excess air coming to the engine is being counter-acted by the computer to push more fuel. Try the blocking the opening of the incoming air to your throttle valve with a piece of clean rag or your palm. The engine is supposed to stop when you do this and if it continues to run, it means you have a serious vacuum leak. The same solution for fixing the vacuum leak can be used as described above.

Bad fuel system:

P0174 can be triggered by weak fuel pressure especially if the the fuel pump is worn. Another factor to consider is fuel blockage in the fuel lines which can deprive fuel flow in the incoming air and fuel mixture. A quick fuel pressure test can do this or try testing the fuel drop pressure in the fuel lines.

P0174 common fixes:

On GM vehicles, P0174 can occur when the cruise control is applied. if this happens, check the plastic tubings for your vacuum hose connections connected to the cruise control. Some of them could crack and cause a massive vacuum leak and trigger a P0174. You will not get P0174 in town driving but can occur once you drive the vehicle in the highway and use your cruise control.

Ford P0174 codes usually occur near or behind the IAC or idle control valve. You can check this by running the engine at idle and spraying a carb cleaner at the IAC area. When spraying, watch out for exhaust piping or parts which can burst and cause a fire. This IAC is notorious for having a vacuum leak failure due to poor connections and sometimes, it is better to wiggle the loose parts while you are spraying to expose the leak.

P0174 on European vehicles is almost always caused by two factors: vacuum leak and defective mass air flow sensor. Use the same guidelines above for finding the leak or faulty sensor. ATS can provide you a detailed tests and diagrams if you are a member.

P0174 codes on Imports is also caused the two most common culprits: vacuum leak or defective mass sensor and the same guideline above apply.

Thanks!