Definition: The fuel economy, as measured by an actual road test, is noticeably lower than expected. Also, the economy is noticeably lower than the symptom was on this vehicle at one time, as previously shown by an actual road test.

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

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Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

1. Perform a bulletin search.
2. If you find a bulletin that addresses the symptom, correct the condition as instructed in the bulletin.

Did you find a bulletin that addresses the symptom?

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Go to Step 19

Go to Step 3

Perform the careful visual/physical checks as described at the start of the Symptoms section.

Did you perform the visual/physical check?

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Go to Step 4

Go to Important Preliminary Checks

Check the owner's driving habits.

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Go to Step 5

Go to Step 6

Review the items in Step 4 with the customer and advise as necessary.

Is the action complete?

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System Normal

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1. Visually (physically) check the Vacuum hoses for splits, kinks, and improper connections and routing as shown on the Vehicle Emission Control Information label.
2. If a problem is present, repair the problem as necessary.

Was a repair necessary?

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Go to Step 19

Go to Step 7

1. Remove and check the air filter element for dirt, or for being restricted. Refer to Air Cleaner .
2. Replace the air filter element if necessary.

Did the air filter require replacement?

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Go to Step 19

Go to Step 8

1. Check for the proper fuel pressure. Refer to Fuel System Diagnosis .
2. If a problem is present, repair the problem as necessary.

Was a repair necessary?

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Go to Step 19

Go to Step 9

Notice: If spark plugs are gas or oil fouled, determime the cause of the fouling before replacing the spark plugs in order to avoid damage to the new spark plugs.

1. Remove the spark plugs.
2. Check the spark plugs for the following conditions:

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Wet plugs

•

Cracks

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Wear

•	Improper gap

•	Burned electrodes

•	Heavy deposits

3. If a problem is present, repair the problem as necessary.

Was a repair necessary?

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Go to Step 19

Go to Step 10

1. Check the engine coolant level for being low. Refer to Engine Cooling.
2. If a problem is present, repair the problem as necessary.

Was a repair necessary?

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Go to Step 19

Go to Step 11

1. Check for an incorrect or a malfunctioning engine thermostat. Refer to Engine Cooling .
2. If a problem is present, repair the problem as necessary.

Was a repair necessary?

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Go to Step 19

Go to Step 12

1. Check the engine compression for being low. Refer to Engine Mechanical.
2. If a problem is present, repair the problem as necessary.

Was a repair necessary?

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Go to Step 19

Go to Step 13

1. Check the TCC operation.
2. If a problem is present, repair the problem as necessary.

Was a repair necessary?

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Go to Step 19

Go to Step 14

1. Check the exhaust system for a possible restriction.
2. Inspect the exhaust system for any damaged or collapsed pipes.
3. Inspect the muffler for heat distress or for a possible internal failure.
4. Check the exhaust system for a possible plugged three-way catalytic converter by checking the exhaust system back pressure. Refer to Restricted Exhaust System Check .
5. If a problem is present, repair the problem as necessary.

Was a repair necessary?

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Go to Step 19

Go to Step 15

1. Connect the J 33431-B (Signal Generator) to the VSS electrical connector in order to check for proper calibration of the speedometer.
2. With the ignition ON, turn the tester ON and monitor the speedometer and the speed displayed on a scan tool.

Does the speed indicated on the speedometer closely match the vehicle speed displayed on the scan tool?

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Go to Step 17

Go to Step 16

Diagnose and repair the inaccurate speedometer condition as necessary. Refer to Electrical Diagnosis.

Is the action complete?

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Go to Step 19

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1. Check the air intake system and the crankcase ventilation system for any air leaks.
2. If a problem is present, repair the problem as necessary.

Was a repair necessary?

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Go to Step 19

Go to Step 18

1. Review all of the diagnostic procedures within this table.
2. When all of the procedures have been completed and no malfunctions are present, visually/physically inspect the following items:

•	The scan tool data

•	All of the connections within a suspected circuit and/or system.

3. If a problem is present, repair the problem as necessary.

Is the action complete?

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Go to Step 19

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Operate the vehicle within the conditions under which the original symptom was observed.

Does the system now operate properly?

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System OK

Go to Step 2