Diagnosis & Repair
- Check with vehicle driver if fuel tank cap was found loose at any time. If fuel tank cap was loose, it probably was cause of DTC P0440 to set. If fuel tank cap was not loose, check for cracks, deformations or loose connections in the following:
- Fuel tank.
- Charcoal canister.
- Fuel tank filler pipe.
- Hose and tubes around fuel tank and charcoal canister.
Repair as necessary. If components are okay, go to next step.
- Check if fuel tank cap is an original manufacturer's cap. If fuel tank cap is an original manufacturer's cap, go to next step. If fuel tank cap is not an original manufacturer's cap, replace cap with a manufacturer's cap.
- Check if fuel tank cap is installed properly. Reinstall fuel cap as necessary. If fuel cap is installed properly, go to next step.
- Check for damaged fuel tank cap and gasket. Replace fuel cap as necessary. If fuel tank cap and gasket are okay, go to next step.
- Remove fuel tank cap. Visually inspect fuel tank filler neck for damage. Replace filler neck as necessary. If filler neck is okay, go to next step.
- Check vacuum hoses between vapor pressure sensor and vapor pressure sensor VSV, and between vapor pressure sensor and charcoal canister. Check hoses for correct installation, looseness and damage. Repair as necessary. If vacuum hoses are okay, go to next step.
- Check hose and tube between fuel tank and charcoal canister for correct installation and damage. Repair as necessary. If hose and tube are okay, go to next step.
- Visually inspect charcoal canister for cracks or damage. Replace canister as necessary. If canister is okay, go to next step.
- Access ECM under front of carpet on passenger side of vehicle. Turn ignition on. Backprobing, measure voltage between terminals No. 2 (Blue/Black wire) and No. 18 (Brown wire) at ECM E16 connector. See Figure. If voltage is 4.5-5.5 volts, go to next step. If voltage is not 4.5-5.5 volts, replace ECM and retest system.NOTE: Vehicle may be equipped with one of 2 different types of vapor pressure sensor. Sensor is mounted on top of fuel tank and may either have 2 vacuum ports (old style) or no vacuum ports (new style).
- Locate vapor pressure sensor on top of fuel tank. Sensor has a Black 3-pin connector with Brown, Blue/Black and Red wires. Identify type of vapor pressure sensor used. If sensor does not have any vacuum ports, go to next step. If sensor has 2 vacuum ports, disconnect vacuum supply hose from vapor pressure sensor. See Fig 1. Backprobing ECM harness connector, connect voltmeter between terminal No. 22 (Red wire) at ECM E18 connector and terminal No. 18 (Brown wire) at ECM E16 connector. See Figure. Connect a vacuum pump to sensor. Voltage should be 3.0-3.6 volts without vacuum applied, and 1.3-2.1 volts with .59 in. Hg (2.0 kPa) applied. If voltage is as specified, go to step 13. If voltage is not as specified, go to step 12.
- Backprobing ECM harness connector, connect voltmeter between terminal No. 22 (Red wire) at ECM E18 connector and terminal No. 18 (Brown wire) at ECM E16 connector. See Figure. Remove fuel tank cap and note voltmeter reading. If voltage is 3.0-3.6 volts, go to step 13. If voltage is not 3.0-3.6 volts, go to next step.
- Check for an open or short circuit in wiring harness between vapor pressure sensor and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If wiring is okay, replace vapor pressure sensor.
- Check fuel tank and fuel tank overfill check valve for cracks and damage. Overfill check valve is located on top of fuel tank. Replace fuel tank or overfill check valve as necessary. If fuel tank and overfill check valve are okay, probable cause of DTC P0440 to set was an incorrectly installed fuel tank cap.