System Diagnosis - Fuel System

No Start Problem

Some failures of this system will result in an Engine Cranks But Will Not Run symptom. If this condition exists, Refer to Computers and Control Systems / Diagnosis by Symptom / Procedures / Diagnostic Tables / System Diagnostic Tables / 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.
Testing and Inspection

Refer to Computers and Control Systems / Diagnosis by Symptom / Procedures / Diagnostic Tables / System Diagnostic Tables / Fuel Pump Relay Circuit Diagnosis for the fuel system wiring schematic.
Testing and Inspection

Fuel Delivery Problem

If there is a fuel delivery problem, Refer to Computers and Control Systems / Diagnosis by Symptom / Procedures / Diagnostic Tables / System Diagnostic Tables / 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 Computers and Control Systems / Diagnosis by Symptom / Procedures / Diagnostic Tables / Diagnostic Trouble Code Tables / DTC P0171 Fuel Trim System Lean or DTC P0172 Fuel Trim System Rich.
Testing and Inspection