Some failures of this system result in an Engine Cranks But Will Not Run symptom. If this condition exists, refer to Engine Cranks but Does Not Run . This determines if the problem is caused by the ignition system, the PCM, or the fuel pump electrical circuit.

Refer to Fuel Pump Electrical Circuit Diagnosis for the fuel system wiring schematic.

If there is a fuel delivery problem, refer to Fuel System Pressure Test . This diagnoses the fuel injectors, the fuel pressure regulator, and the fuel pump. If a malfunction occurs in the fuel metering system, the condition usually results in either a rich HO2S signal or lean HO2S signal. This condition is indicated by the HO2S voltage, causing the PCM to change the fuel calculation (fuel injector pulse width) based on the HO2S reading. Changes made to the fuel calculation are indicated by a change in the long term fuel trim values which may be monitored with a scan tool. Ideal long term fuel trim values are around 0%. For a lean HO2S signal, the PCM adds fuel, resulting in a fuel trim value above 0% and for a rich HO2S signal the PCM takes away fuel, resulting in a fuel trim value below 0%. Some variations in fuel trim values are normal due to power train design. If the fuel trim values are excessively more or lower then 0% refer to DTC P0172 Fuel Trim System Rich .

The scan tool displays idle air control (IAC) pintle position in counts. 0 counts indicate that the PCM is commanding the IAC pintle to be driven all the way into a fully seated position. This is usually caused by a vacuum leak.

The higher the number of counts, the more air is being commanded to bypass the IAC pintle. Refer to Idle Air Control (IAC) System Diagnosis in order to diagnose the IAC system.

The TP sensor is mounted on the side of the throttle body opposite the throttle lever. The TP sensor measures the throttle valve angle, and relays that information to the PCM. Knowledge of the throttle angle is needed by the PCM to generate the required injector control signals. For further information, refer to Information Sensors/Switches Description .

The MAF sensor is mounted to the front of the throttle body, and is used to measure the amount of air entering the engine. The PCM uses this information to determine the operating condition of the engine and to control fuel delivery. For further information, Refer to Information Sensors/Switches Description .

A fuel system pressure test is part of several of the diagnostic routines and symptom checks. To perform this test, refer to Fuel System Pressure Test .