Some failures of this system will result in an Engine Cranks But Will Not Run symptom. If this condition exists, refer to Engine Cranks but Does Not Run . This will determine 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 the 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, it 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 will be indicated by a change in the long term fuel trim values which can be monitored with a scan tool. Ideal long term fuel trim values are around 0 percent; for a lean HO2S signal, the PCM will add fuel, resulting in a fuel trim value above 0 percent and for a rich HO2S signal the PCM will take away fuel, resulting in a fuel trim value below 0 percent. Some variations in fuel trim values are normal due to power train design. If the fuel trim values are excessively more or less than 0 percent refer to DTC P0171 Fuel Trim System Lean or DTC P0172 Fuel Trim System Rich .

The scan tool displays the idle air control (IAC) pintle position in counts. 0 counts indicates 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 the Idle Air Control (IAC) System Diagnosis in order to diagnose the IAC system. Refer to Rough, Unstable, or Incorrect Idle and Stalling for other possible causes of idle problems.

The TP sensor is mounted on the side of the throttle body opposite the throttle lever. The TP sensor detects 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, or pulses. For further information, refer to Information Sensors/Switches Description .

The MAF sensor is located in the duct between the throttle body and the air cleaner 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 charts and symptom checks. To perform this test, refer to the Fuel System Pressure Test .