
P0174 System Too Lean (Bank 2)
Content
P0174 System Too Lean (Bank 2)
Technical description
The system is too poor (bank 2)
What does this mean?
This Diagnostic Trouble Code (DTC) is a generic transmission code, which means it applies to OBD-II equipped vehicles. Affected vehicle brands include, but are not limited to, Ford, Lexus, Chevy, BMW, Toyota, Jaguar, Acura, Volvo, Nissan, etc. Although generic, specific repair steps may vary by brand / model / engine. Ironically, this code seems to be more common in Ford and Chevy vehicles.
Every vehicle has a PCM or ECM (Powertrain/Engine Control Module). Essentially the “brain” or main computer of the vehicle, its job is to monitor various sensor readings and use that information to operate the engine most efficiently under current conditions.
Basically, this P0174 code means that the upstream oxygen sensor on bank 2 is 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 does not have cylinder #1.
The engine uses what are called O2 or oxygen sensors in the exhaust stream to determine the air-fuel ratio in the exhaust gases leaving the engine. The PCM (or ECM) uses this information to determine how much fuel to inject through 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 running efficiently and with low emissions.
If the O2 sensor tells the PCM by reading that there is too much air in the exhaust, the PCM compensates by adding more fuel. In this case, it adds more fuel to bank 2. The PCM will only adjust the amount of fuel it will inject up to a certain point in an attempt to bring this air: fuel ratio as close as possible to the optimum. When the PCM reaches its limit for the amount of fuel it will inject but the front (front) oxygen sensor from bank 2 still detects a lean mixture, the PCM will continue to command more than normal bank 2 fuel and run this code. and the MIL (Malfunction Indicator Lamp) comes on.
Scanner displays code P0174:
However, now there is an interesting point. This code can be set because the PCM thinks it is sending more fuel to the bank 2 injectors, but they don't actually use more fuel. In other words, this code may have been set due to a refueling problem. Additional possible causes of this code are listed later in this article.
Note. This DTC is very similar to P0171, which is a simplified code for bank 1, and in fact, your car can display both codes at the same time. In the case of some Fords (eg 4.6L or 5.4L V8) it is common to see P0171 and P0174 at the same time.
symptoms
You will most likely not notice any drivability issues as a result of the P0174 code, although there may be symptoms such as:
- lack of power
- increased fuel consumption
- detonation (spark detonation)
- wobble / jump with acceleration
reasons
The P0174 code may mean that one or more of the following events have occurred:
- The mass air flow (MAF) sensor is dirty or defective (if equipped). Note. Using "oil" air filters can result in contamination of the MAF if the filter is overly lubricated. There is also a problem with some vehicles in which the MAF sensors leak the silicone sealing material used to protect the circuit.
- Possible vacuum leak downstream of the MAF sensor.
- Fuel problem (rail / nozzles / pump / regulator)
Possible solutions
If you encounter this code, don't assume the O2 oxygen sensor is faulty and replace it first! Please do an accurate diagnosis before purchasing parts. Correct step-by-step diagnostics will ultimately save you money and you will usually learn new things.
We are unable to specify specific steps for repairing a vehicle as they may vary depending on the year of manufacture, make, model and engine of your particular vehicle. However, we do provide some general diagnostic information that will hopefully help you solve your minimum P0174 code.
Possible solutions include:
- In many cases, simple cleaning of the MAF sensor helps. If you need help, refer to the service manual for its location. I find it best 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 is dry before reinstalling.
- Inspect all vacuum and PCV hoses and replace if necessary.
- Check if the fuel filter is dirty and if the fuel pressure is correct.
External links
Here are some links you might find helpful:
- Ford F150 P0171 / P0174 Codes Information
- EasyAutoDiagnostics Ford 171/174
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NOTE. This information is provided for informational purposes only. It is not intended to be used as a repair recommendation and we are not responsible for any action you take on any vehicle. All information on this site is protected by copyright.

