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 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%; 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 Bank 1 , DTC P0172 Fuel Trim System Rich Bank 1 ,DTC P0174 Fuel Trim System Lean Bank 2 , or DTC P0174 Fuel Trim System Lean Bank 2 .
Always start with the A Powertrain On Board Diagnostic (OBD) System Check . This will reduce diagnosis time and prevent unnecessary parts replacement. Diagnosis of the fuel metering system is covered in this starting with the, Fuel System Diagnosis . This table cover the diagnosis of the injectors, pressure regulator, and the fuel pump.
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%, 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%, 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 check.
Alcohol concentrations greater than 10% 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 .
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 Engine Controls Components Fuel Injectors OBD II Symbol Description Notice ESD Notice and Engine Controls Components Fuel Injectors OBD II Symbol Description Notice ESD Notice for an electrical diagram of this circuit.
The Fuel System Check provides a quick analysis of the fuel system. This chart then identifies more detailed diagnosis required based on the symptoms present.
The Fuel Leak/Odor Check provides a means of identifying a fuel system component that is causing a leak. This also provides information on how to diagnosis a fuel odor condition.
Number(s) below refer to the step number(s) on the Diagnostic Table.
If the engine does not start or stay running and there is no fuel pressure check all components and circuit grounds.
The vehicle should be operated the same conditions as when the leak/odor occurs.
Step
Action
Value(s)
Yes
No
1
Was the Powertrain On-Board Diagnostic (OBD) System Check performed?
--
Go to Step 2
Go to A Powertrain On Board Diagnostic (OBD) System Check
2
Were you sent here from a DTC table?
Go to Step 4
Go to Step 3
3
Key On install the Scan Tool.
Are any PCM DTC(s) set?
Diagnose those DTC(s) first
4
Crank the engine.
Does the engine start and stay running?
Go to Step 5
Go to Fuel System Pressure Test
5
Is there a fuel leak or odor complaint?
Go to Step 10
Go to Step 6
6
Is there a fuel odor complaint?
Go to Step 11
Go to Step 7
7
Is there a fuel gage complaint?
Go to Electrical Diagnosis Instrument Panel Displays
Go to Step 8
8
Is there a economy complaint?
Go to Poor Fuel Economy
Go to Step 9
9
Are there any other driveability symptoms?
Fuel System OK
10
Try to duplicate customer complaint.
Is there a fuel leak?
Go Step 12
Go to Excessive Exhaust Emissions or Odors
11
Is there a fuel odor?
Fuel system OK
12
Repair fuel leak.
Is the repair complete?
The Idle Speed Control Check verifies proper IAC valve operation.
This check test the IAC valve to make sure that it is moving in and out without binding.
This procedure checks the circuits to determine if one or more is open or shorted.
Was the Powertrain On Board Diagnostic (OBD) System Check performed?
Go to Powertrain OBD System Check
Connect the scan tool.
Are any other DTC's set?
Go to DTC(s) that are set
Does the Engine Speed remain within the specified value of Desired Idle for each RPM command?
50 RPM
Fault not present
Does each node light cycle red and green (never Off)?
Was a problem found and repaired?
Verify repair
Visually/physically inspect for the following conditions:
Do any of the above require a repair?
Refer to appropriate section for on-vehicle service
Check for poor terminal contact at the IAC harness connector.
Replace the IAC valve.
Was terminal contact repaired?
Replace the PCM.
Symptom
Poor cold start
Low volatility
Injector deposits
Refer to Fuel System Diagnosis .
Poor warm up
Low Volatility
Poor cold weather performance
Poor hot start
High Volatility
Poor hot weather performance
Vapor lock
Spark/detonation
Low octane
Poor fuel economy
High volatility
Intake valve deposits
Excessive exhaust emissions
Sulfur deposits
Reduced Power
Improper volitility
Rough/unstable idle
Always begin the fuel and the air control system diagnosis with, Fuel System Check. This chart will identify other charts for specific checks, such as:
If there is no fuel pressure check all component and circuit grounds.
Fuel system deposits can cause various driveability problems. Deposits usually occur during hot soaks after key Off. Poor fuel quality or driving patterns such as short trips followed by long cool down periods can cause injector deposits. This occurs when the fuel remaining in the injector tip evaporates and leaves deposits. Leaking injectors can increase injector deposits. Deposits on fuel injectors affect their spray pattern, which in turn could cause reduced power, unstable idle, hard starts and poor fuel economy.
Intake valve deposits can also be related to fuel quality. While most fuels contain deposit inhibitors, some do not and the effectiveness of deposit inhibitors varies by manufacturer. If intake valve deposits occur, fuel may be suspected. These deposits can cause symptoms such as excessive exhaust emissions, power loss and poor fuel economy.
