For 1990-2009 cars

#### Poor Fuel Economy Symptom

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
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.
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

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?

--

Go to Step 19

Go to Step 3

3 | Was visual/physical check performed? | -- | Go to Step 4 | Go to Important Preliminary Checks
4 | Check the owners driving habits.

• | Is A/C ON full time (Defroster mode ON)?

• | Are tires at the correct pressure?

• | Are excessively heavy loads being carried?

• | Is accelerating too much, too often?

--

Go to Step 5

Go to Step 6

5 | Review the items in Step 4 with customer and advise as necessary. Is the action complete? | -- | System Normal | --
6 |

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

Was a repair required?

--

Go to Step 19

Go to Step 7

7 |

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

Was a repair required?

--

Go to Step 19

Go to Step 8

8 |

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

Was a problem found?

--

Go to Step 19

Go to Step 9

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 for wet plugs, cracks, wear, improper gap, burned electrodes, or heavy deposits.
3. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 19

Go to Step 10

10 |

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

Was a problem found?

--

Go to Step 19

Go to Step 11

11 |

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?

--

Go to Step 19

Go to Step 12

12 |

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

Was a problem found?

--

Go to Step 19

Go to Step 13

13 |

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

Was a problem found?

--

Go to Step 19

Go to Step 14

14 |

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. Refer to Restricted Exhaust System Check .
5. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 19

Go to Step 15

15 |

1. Connect the J 33431-B (Signal Generator) to the VSS electrical connector 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?

--

Go to Step 17

Go to Step 16

16 | Diagnose and repair inaccurate speedometer condition as necessary. Refer to Section 8A-33. Is the action complete? | -- | Go to Step 19 | --
17 |

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

Was a problem found?

--

Go to Step 19

Go to Step 18

18 |

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

• | Visual/physical inspection.

• | Scan tool data.

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

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

Was a problem found?

--

Go to Step 19

Check for Service Bulletins

19 | Operate vehicle within the conditions under which the original symptom was noted. Does the system now operate properly? | -- | System OK | Go to Step 2