Air Metering and Fuel Delivery Codes

This group covers the codes that monitor how much air enters the engine and how much fuel is injected to match it: mass air flow (MAF) and manifold pressure (MAP) sensors, intake air temperature, throttle position, oxygen sensors and the fuel trims themselves.

The computer tries to hold the ideal mixture, about 14.7 parts of air to 1 part of gasoline by weight. When it has to correct the mixture too much, or when a sensor gives an impossible reading, it stores a code from this family. These are the most common codes on high-mileage gasoline engines.

Most searched codes in this system

• P0171 and P0174: lean mixture on bank 1 and bank 2.
• P0172 and P0175: rich mixture.
• P0101 to P0103: MAF sensor range and circuit.
• P0106 and P0107: MAP sensor.
• P0130 to P0141: oxygen sensors and their heaters.

What to check first

1. Look for vacuum leaks in the hoses, the intake manifold gasket and the crankcase ventilation (PCV) system.
2. Clean the MAF sensor with a dedicated MAF cleaner, never with compressed air.
3. Read the fuel trims at idle and at 2,500 rpm before replacing any sensor.
4. Check the fuel pressure if the mixture goes lean under load.