For 1990-2009 cars

#### Poor Fuel Economy

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

• | Refer to Diagnostic System Check - Engine Controls .

• | Refer to Symptoms - Engine Controls .

• | Check the air cleaner element for dirt or restrictions.

• | Visually and physically check the vacuum hoses for splits, kinks, and proper connections as shown on the Vehicle Emission Control Information label.

• | Check the owners driving habits for any of the following:

- | The A/C system defroster mode is ON all the time.

- | The tires are improperly inflated.

- | Heavy loads are frequently being carried.

- | Heavy acceleration and high speeds are common.

- | Frequent short trips

- | Prolonged periods of idling

- | Driving on unpaved or rough roads

• | Suggest that the owner refill the fuel tank and recheck the fuel economy.

Fuel System Checks |

• | Check the type, quality, and alcohol content of the fuel. Oxygenated fuels have lower energy and may deliver reduced fuel economy. Refer to Fuel System Specifications and Alcohol/Contaminants-in-Fuel Diagnosis .

• | Check for the correct fuel pressure. Refer to Fuel System Diagnosis .

Ignition System Checks |

• | Inspect the spark plugs for correct operation and good ignition system performance. Refer to Spark Plug Inspection .

• | Check the ignition coil boots for cracking, chafing, and loose connections.

• | Observe the Spark parameter on the scan tool at idle, while operating the rear defogger, the A/C system, or the headlights. If the scan tool display remains fixed at 10 degrees, check for a short to ground in the Diagnostic Request circuit from the powertrain control module (PCM) connector C2 terminal 15 to the underhood diagnostic link connector.

• | Check the knock sensor (KS) and the sensors circuit shielding. The knock sensor is not diagnosed for excessive activity. A faulty knock sensor or signal interference could cause excessive retard of the ignition timing advance. Observe the Spark parameter on a scan tool and compare with a known good vehicle. A typical value in OD at 104.6 km/h (65 mph) is 26-32 degrees.

Cooling System Checks |

• | Check the engine coolant level.

• | Check the engine thermostat for always being open or for the wrong heat range. Refer to Thermostat Diagnosis in Engine Cooling.

Additional Checks |

• | Check the clutch adjustment in vehicles equipped with a manual transmission. Refer to Clutch Slipping in Clutch.

• | Check the transmission shift pattern and the torque converter clutch (TCC) operation in vehicles equipped with an automatic transmission. Refer to Symptoms - Automatic Transmission in Automatic Transmission-3 speed or Symptoms - Automatic Transmission in Automatic Transmission-4 speed.

• | Check for dragging brakes.

• | Check for uneven or premature tire wear. A suspension misalignment can cause reduced fuel economy. Refer to Wheel Alignment Measurement in Wheel Alignment.

• | Verify that the tires and wheels are similar to OEM. Wide performance tires create more drag and taller tires can cause odometer discrepancies.

• | Check for the speedometer for proper calibration. Refer to Speedometer and/or Odometer Inaccurate or Inoperative in Instrument Panel, Gages, and Console.

• | Check for a green engine. Fuel economy may not be near expected levels until the engine has had 5 000-8 000 km (3,000-5,000 miles) to break in.

• | Check for add-on equipment like luggage racks and carriers. Wind resistance can lower fuel economy.

• | Check the Service Bulletins for any updates or information.