Diagnosis
Although you can diagnose the error code P0174 yourself, you’ll need specialized equipment to read fuel trim values, which are crucial for this repair job. Fuel trim values are what the engine control module uses to compensate for all problems relating to airfuel mixture ratios.
So, it’s best to let a professional mechanic handle the diagnosis for you, to avoid further damage.
Here’s how your mechanic will diagnose the problem:
1. First, your mechanic will analyze your short term fuel trim values, long term fuel trim values, and freeze frame data.
2. If you have a dirty MAF sensor, the fuel trim values will increase as your engine speed increases. So, your mechanic will use a scan tool to test your mass air flow sensor.
3. They’ll also inspect your air filter to ensure it’s not letting dust or debris clog up your MAF sensor.
4. Then, they’ll check your fuel system for issues, such as a weak fuel pump, by performing a fuel pressure regulator test.
5. They’ll also inspect your fuel injector and fuel filter components to see if they’re dirty or clogged.
6. Next, they’ll check if an intake leak in your intake system or vacuum lines allows particles to enter your engine.
7. Then, the mechanic will inspect your spark plug wells and rubber grommets for oil. Defective valve covers can also cause an oil leak.
8. They’ll check to see if your PCV valve and EGR valve are defective — allowing too much air into your air fuel mixture.
9. Finally, your mechanic will use a scan tool to test the air fuel ratio of your oxygen sensor (O2 sensor).
Your mechanic must complete the diagnostic process before attempting repairs. You don’t want to pay for a new MAF sensor when your O2 sensor is the root cause of the lean fuel condition.
Note: Short term and long term fuel trim values help identify fuel system problems, such as a weak fuel pump, dirty fuel injector, low fuel pressure, intake manifold leak, etc. The short term fuel trim values measure immediate changes to your car’s oxygen levels, while long-term values measure O2 levels over a longer period.