DEFINITION: Fuel economy, as measured by an actual road test, is noticeably lower than expected. Also, economy is noticeably lower than it was on this vehicle at one time, as previously shown by an actual road test.

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

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Go to Step 2

Go to the Powertrain On Board Diagnostic (OBD) System Check

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

Was a bulletin found that addresses the symptom?

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Go to Step 18

Go to Step 3

Was visual/physical check performed?

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Go to Step 4

Go to Visual/Physical 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 customer and advise as necessary.

Is action complete?

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System OK

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1. Visually/physically check vacuum hoses for splits, kinks, and improper connections and routing. Refer to Emission Hose Routing Diagram .
2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 18

Go to Step 7

1. Remove and inspect the air filter element. Go to Air Cleaner Element .
2. Replace the air filter element if necessary.

Was a problem found?

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Go to Step 18

Go to Step 8

1. Remove the spark plugs.
2. Check for wet plugs, cracks, wear, improper gap, burned electrodes, or heavy deposits.
3. If a problem is found, repair as necessary.

Notice: Determine the cause of the oil or gas fouled spark plugs in order to avoid damage to the new spark plugs.

Was a problem found?

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Go to Step 18

Go to Step 9

1. Check for low engine coolant level. Refer to Cooling System Diagnosis in Engine Cooling.
2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 18

Go to Step 10

1. Check for an incorrect or faulty engine thermostat. Refer to Thermostat Diagnosis in Engine Cooling.
2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 18

Go to Step 11

1. Check for low engine compression. Refer to Engine Compression Test.
2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 18

Go to Step 12

1. Check TCC operation. Refer to 4T60-E Automatic Transaxle Diagnosis.
2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 18

Go to Step 13

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

Was a problem found?

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Go to Step 18

Go to Step 14

1. Check for proper calibration of speedometer:

-	Install a J 33431-C Signal Generator And Instrument Panel Tester.

-	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 16

Go to Step 15

Diagnose and repair inaccurate speedometer condition as necessary. Refer to Vehicle Speed Sensor in Electrical Diagnosis.

Is action complete?

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Go to Step 18

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1. Check the the following items for air or vacuum leaks:

•	Intake manifold.

•	Throttle body.

•	EGR valve and pipes

•	Crankcase.

2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 18

Go to Step 17

1. Review all diagnostic procedures within this table.
2. When all procedures have been completed and no malfunctions are found, review/inspect the following:

•	Visual/physical inspection. Go to Visual/Physical Checks .

•	Scan tool data. Go to Engine Scan Tool Data List .

•	Freeze Frame data/Failure Records Data.

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

1. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 18

Review technical bulletins

Operate the vehicle to duplicate conditions present when the original symptom was noted.

Is symptom still present?

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Go to Step 3

System OK