System Diagnosis - Fuel System

Engine Controls (Fuel Pump Relay And The Theft Deterrent System):

Fuel Metering System

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.
Engine Cranks, But Will Not Run
This will determine if the problem is caused by the ignition system, the Powertrain Control Module (PCM), or the fuel pump electrical circuit.

If there is a fuel delivery problem, Refer to Fuel System Pressure Test.

System Diagnosis - 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 Heated Oxygen Sensor (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%; for a lean HO2S signal, the PCM will add fuel, resulting in a fuel trim value above 0% and for a rich HO2S signal the PCM will take 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 greater or
lower then 0%.Refer to DTC P0171 Fuel Trim System Lean P0171
or DTC P0172 Fuel Trim System Rich.
P0172