| CAUTION | If ECM replacement is instructed in following testing, always ensure ECM harness connector and ground circuit are okay. If either are suspect, repair and repeat testing to confirm ECM malfunction. If ECM is replaced, ECM must be programmed with proper ignition key code for engine immobilizer system. For programming procedures, see COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION. |
Circuit Description
Vapor pressure sensor, canister closed valve Vacuum Switching Valve (VSV) and pressure switching valve VSV are used to detect faults in EVAP system. ECM determines if a fault is present in EVAP system based on the vapor pressure signal circuit. DTC P0440 is set if EVAP system leak is detected or vapor pressure sensor malfunctions (detection of atmospheric pressure in fuel tank, after vehicle has been driven for 20 minutes). Possible causes are
- Faulty vapor pressure sensor.
- Fuel tank cap installed incorrectly.
- Fuel tank cap defective.
- Damaged, disconnected or blocked vacuum hose.
- Fuel tank damaged.
- Charcoal canister damaged.
- Hose between fuel tank and charcoal canister damaged.
- Open or short in vapor pressure sensor circuit.
- Fuel tank overfill check valve damaged.
- Faulty ECM.
Note. If DTC P0441, P0446, P0450 or P0451 is output after DTC P0440, perform appropriate diagnostic test first before performing DTC P0440 test.
Diagnostic Aids
Ask customer if fuel cap has been left off or not completely tightened recently. This may cause DTC to be set. Using scan tool, read freeze frame data. Freeze frame records engine conditions when malfunction is detected.