DTC Test No. 21 - EVAP Emission Control System Small Leak Detected

NOTE: Possible causes for DTC are: improper tightening of fuel tank cap, defective fuel vent valve, restricted or broken purge or vapor line, broken fuel tank seal, defective EVAP purge solenoid, defective EVAP ventilation solenoid, defective fuel tank differential pressure sensor, defective engine coolant temperature sensor or intake air temperature sensor, defective power steering pressure switch, incorrect fuel, improper fuel tank cap, defective or restricted EVAP canister.

The Engine Control Module (ECM) turns EVAP ventilation solenoid on in order to shut off outside air port on EVAP canister. The ECM then operates EVAP purge solenoid to generate a negative pressure in the fuel tank and purge lines. When negative pressure exists in fuel tank and purge lines, the EVAP purge solenoid shuts off and fuel tank and purge lines are sealed. Once fuel tank and purge lines are sealed, the pressure differences inside the fuel tank are monitored. If there is a large decrease in the pressure over a given time, the ECM determines there is a leak in the fuel tank or purge lines. If fuel tank pressure does not drop even if the EVAP purge solenoid is operating while outside air port on EVAP canister is shut off due to blockage in purge line or because fuel tank cap is loose, the ECM determines there is a problem with the EVAP system. If ECM determines there is a leak or a problem in the EVAP system, the ECM will illuminate the Malfunction Indicator Light (MIL) on the instrument panel. The EVAP ventilation solenoid is located near EVAP canister. See Fig 1 and Fig 2 . On FWD models, EVAP canister is located in the fuel tank. On AWD models, EVAP canister is located at driver's side front corner of engine compartment, near headlight assembly. EVAP purge solenoid is located on intake manifold. See Fig 3 . EVAP purge solenoid may also be referred to as EVAP purge solenoid valve.

Fig 1: Locating EVAP Ventilation Solenoid & EVAP Canister (FWD Models)

Fig 2: Locating EVAP Ventilation Solenoid & EVAP Canister (AWD Models)

Fig 3: Locating EVAP Purge Solenoid
Remove fuel tank cap. Push flapper in fuel tank filler tube assembly downward to operate flapper valve. Reinstall and tighten fuel tank cap. Remove fuel tank cap. Check that distance from tip of fuel tank filler tube assembly to flapper valve is at least 1.1" (28 mm). If distance is within specification, go to next step. If distance is not within specification, replace fuel tank filler tube assembly.
Disconnect hose from air filter that goes to the EVAP ventilation solenoid. Ensure hose is disconnected at air filter and not the EVAP ventilation solenoid. Air filter and EVAP ventilation solenoid are located near EVAP canister. See Fig 1 and Fig 2 . Plug end of hose.
CAUTION: DO NOT apply more than .57 psi (3.9 kPa) when checking EVAP system or fuel tank may be cracked. Ensure scan tool is used to check the pressure reading when applying pressure on EVAP system.
Note location of purge hose that goes from EVAP purge solenoid back to the EVAP canister. Purge hose is connected to pipe that goes over air intake plenum and back to EVAP canister. Disconnect purge hose at the pipe. Using "T" fitting, connect vacuum pump between disconnected purge hose and pipe.
Connect scan tool to data link connector. Set scan tool to display scan tool service data for FUEL TANK DIFFERENTIAL PRESSURE SENSOR. Scan tool is used to read amount of pressure applied on the EVAP system.
Watch reading on scan tool while using vacuum pump to apply .42 psi (2.9 kPa) of pressure on EVAP system. DO NOT apply more than .57 psi (3.9 kPa) or fuel tank may be cracked.
NOTE: If fuel tank has low fuel level, it may be necessary to operate vacuum pump several times to apply pressure on EVAP system. Pressure may also be applied on EVAP system by starting and warming engine until coolant temperature is more than 140°F (60°C). Increase engine speed to 1600-2000 RPM. Have an assistant monitor pressure reading on scan tool while disconnecting connector from EVAP purge solenoid. When pressure reaches .42 psi (2.9 kPa), immediately decelerate engine to an idle.
If .42 psi (2.9 kPa) can be obtained, go to next step. If .42 psi (2.9 kPa) cannot be obtained, check for a clogging or large leak. See INSPECTION PROCEDURE NO. 50 under TROUBLE SYMPTOMS at end of DTC TESTS.
NOTE: If fuel temperature is high, the vapor pressure may cause the pressure to increase more than .057 psi (.4 kPa) without a leak in the EVAP system. Fuel temperature should be kept at 104°F (40°C) when checking for a leak.
To continue checking for a leak, after 20 seconds recheck pressure reading on scan tool. If pressure does not increase more than .057 psi (.4 kPa), or does not become less than .36 psi (2.5 kPa), check sensor and EVAP purge control system. See INSPECTION PROCEDURE NO. 52 under TROUBLE SYMPTOMS at end of DTC TESTS. If pressure increases more than .057 psi (.4 kPa), or becomes less than .36 psi (2.5 kPa), check for a small leak. See INSPECTION PROCEDURE NO. 51 under TROUBLE SYMPTOMS at end of DTC TESTS.