The fuel pump relay is located in the rear relay center next to the rear fuse block under the rear seat cushion. Refer to Driveability and Emissions for the locator view. For diagnosis of the fuel pump relay circuit, refer to DTC P0231 Fuel Pump Feedback Circuit Low Voltage .

If there is a fuel delivery problem, refer to Fuel System Pressure Test . This test diagnoses the fuel injectors, the fuel pressure regulator, and the fuel pump. If a malfunction occurs in the fuel metering system, a rich HO2S signal or lean HO2S signal is a result. 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 greater or lower then 0 percent, refer to DTC P0171 Fuel Trim System Lean Bank 1 , DTC P0172 Fuel Trim System Rich Bank 1 , DTC P0174 Fuel Trim System Lean Bank 2 , or DTC P0175 Fuel Trim System Rich Bank 2 .

Always start with the Powertrain On Board Diagnostic (OBD) System Check .

If a malfunction occurs in the fuel metering system, it usually results in either a rich or lean exhaust condition. This condition is sensed by the HO2S, and causes the PCM to change the fuel calculation (injector pulse width). The change made to the fuel calculation is indicated by a change in the short term fuel trim and long term fuel trim values which can be monitored by a scan tool. A momentary change to the fuel calculation is indicated by the short term fuel trim value, while a prolonged change is indicated by the long term fuel trim value. Average fuel trim values are around 0 percent , but vary slightly from engine to engine.

Important: When using a scan tool to observe fuel trim values, remember that if the system is in control, no action is required unless a driveability symptom is present. Listed below are examples of lean and rich conditions with the system in control and out of control.

Important: If both fuel trim values are fixed well below 0 percent, refer to items which can cause the system to run rich. If a driveability symptom exists, refer to the particular symptom in Symptoms for additional items to inspect.

Alcohol concentrations greater than 10 percent in fuel can be detrimental to fuel system components and may cause driveability problems such as hesitation, lack of power, stall, no start, etc.

The problems may be due to fuel system corrosion and subsequent fuel filter plugging, deterioration of rubber components, and/or air-fuel mixture leaning.

Various types and concentrations of alcohol are used in commercial fuel. Some alcohol is more detrimental to fuel system components than others. If an excessive amount of alcohol in the fuel is suspected as the cause of a driveability condition, the following procedure may be used to detect the presence of alcohol in the fuel.

The fuel sample should be drawn from the bottom of the tank so that any water present in the tank will be detected. The sample should be bright and clear. If the sample appears cloudy, or contaminated with water, as indicated by a water layer at the bottom of the sample, this procedure should not be used. The fuel system should be cleaned, refer to Fuel System Cleaning .

1. Take a 100 ml specified cylinder with 1 ml graduation marks, fill the cylinder with fuel to the 90 ml mark.
2. Add 10 ml of water in order to bring the total fluid volume to 100 ml and install a stopper.
3. Shake the cylinder vigorously for 10 to 15 seconds.
4. Carefully loosen the stopper in order to release the pressure.
5. Re-install the stopper and shake the cylinder vigorously again for 10 to 15 seconds.
6. Put the cylinder on a level surface for approximately 5 minutes in order to allow adequate liquid separation.

If alcohol is present in the fuel, the volume of the lower layer, which would now contain both alcohol and water, will be greater than 10 ml. For example, if the volume of the lower layer is increased to 15 ml, this indicates at least 5 percent alcohol in the fuel. The actual amount of alcohol may be somewhat greater because this procedure does not extract all of the alcohol from the fuel.

Refer to

Cell 21: PSP, IAC Valve, Coolant Level Switch

Circuit Description

The Idle Speed Control Check verifies proper IAC valve operation.

Reviewing the Failure Rec. may help diagnose an intermittent failure by showing how long ago and under what conditions a DTC has set.

Number(s) below refer to the step number(s) on the Diagnostic Table.

3. This check test the IAC valve to make sure that it is moving in and out without binding. When the IAC valve is commanded the PCM adjusts the IAC position and spark advance for a desired RPM.