Note. EVAP Diagnostic Station (P/N J41413), or similar, is necessary for accurate diagnosis of EVAP system. This tool will be necessary for vacuum and pressurized leakdown testing of EVAP systems. It is equipped with 2 additional gauges to measure vacuum in inches of mercury (in. Hg), and to measure vapor flow in inches of water (in. H 2 O), within an EVAP circuit.
Circuit Description
Evaporative (EVAP) emission system is checked by applying vacuum to EVAP system and monitoring for a vacuum leak. PCM monitors vacuum level via fuel tank pressure sensor signal. When appropriate, EVAP canister purge valve and EVAP canister vent solenoid are turned on, allowing engine to draw a small vacuum on entire evaporative emission system. After desired vacuum level has been achieved, EVAP canister purge valve is turned off, sealing EVAP system. If a large leak is detected, DTC P0440 will be set.
Conditions required to set DTC are
- No MAP, TPS, IAT, ECT, EGR, BSS or EVAP DTCs set.
- BARO is greater than 72.3 kPa.
- Intake air and coolant temperatures at startup are between 40-95°F (4.2-35°C).
- Difference between intake air and coolant temperatures at start up is less than 12.2°F (6.75°C).
- Fuel tank level sensor reads 15-85 percent.
- Fuel level counts vary by less than 12 counts in .125 second time frame.
- Maximum engine run time is at least 390 seconds.
- Vehicle speed is less than 60 MPH.
- Fuel in tank is not sloshing.
- Difference between actual fuel tank pressure and expected fuel tank pressure is less than PCM's expectations.
Diagnostic Aids
Check gas cap, vacuum canister and all EVAP vacuum hoses, lines and components for damage. Check for faulty connections or damaged harness. Observe EVAP system components displayed on scan tool while moving all related harnesses and connectors. A change in scan tool display indicates fault location. If DTC cannot be duplicated, check scan tool FAILURE RECORDS and FREEZE FRAME data to determine mileage since last DTC was set.