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 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 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 repair required?

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Go to Step 18

Go to Step 7

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

Was a repair required?

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Go to Step 18

Go to Step 8

1. Remove spark plugs and check for wet plugs, cracks, wear, improper gap, burned electrodes, or heavy deposits.

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

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

Was a problem found?

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Go to Step 18

Go to Step 9

1. Check engine coolant level for being low. Refer to 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 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 engine compression for being low. Refer to Engine Mechanical.
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 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 Refer 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.

-	Connect J 33431-C (Signal Generator) to VSS electrical connector.

-	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.

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Go to Step 18

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1. Check Air intake system and crankcase for air leaks. Refer to Air Induction System and Crankcase Ventilation System.
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.

•	Scan Tool data.

•	Freeze Frame data/Failure Records Data.

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

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

Was a problem found?

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Go to Step 18

Refer to Technical Service 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