Circuit Description
During specific operating conditions, the engine control module (ECM) performs various tests on the evaporative emission system. The system tests consist of the following series of events. After ensuring that the evaporative emission (EVAP) purge solenoid valve duty cycle has dropped to 0 percent, indicating that the valve is closed, the ECM commands the EVAP canister vent solenoid valve closed, sealing the system. The ECM monitors the accumulation of vapor pressure within the fuel tank via the fuel tank pressure (FTP) sensor. The EVAP test is aborted if the vapor pressure is too high. If any vapor pressure is measured, the pressure will be used later in order to compensate for a pressure reading during the small leak detection test. If a vacuum is measured which exceeds a calculated limit during vapor accumulation, diagnostic trouble code (DTC) P0440 will set. The EVAP canister purge solenoid valve is then opened. Simultaneously, the vent solenoid is opened. If the vapor pressure does not bleed off or bleeds off too slowly, DTC P0440 is set. Once the EVAP purge solenoid valve reached the desired position for the remainder of the diagnostic test, the vent solenoid will be closed again. This causes a vacuum to be applied to the entire EVAP system. The ECM monitors the vacuum level within the system. If the desired vacuum level cannot be achieved, or if the vacuum level is reached but took too much time, DTC P0455 will set. Once the desired vacuum level is reached, the purge solenoid is closed, sealing the system. The ECM continues to monitor the fuel tank pressure sensor signal, measuring the rate of vacuum decay. If the system holds vacuum, the vent solenoid is opened and the test is completed. In addition to the system tests, the ECM monitors the circuit integrity of the purge solenoid (DTC P0443), the vent solenoid (DTC P0446) and the fuel tank pressure sensor (DTC P0450).
Conditions for Running the DTC
| • | The following DTCs are not set: P0100, P0115, P0116, P0130-P0161, P0300-P0306, P0443, P0446, P0450, P0500, P0506, P0507, P0560, P1120 or P1220. |
| • | The vehicle speed is 0 km/h (0 mph). |
| • | The engine is at idle. |
| • | The engine coolant temperature (ECT) at start is between -8°C (17°F) and 75°C (167°F). |
| • | Fuel system is in closed loop. |
| • | The engine load is less than 30 percent. |
| • | The intake air temperature (IAT) is between -8°C (17°F) and 50°C (122°F). |
| • | The system voltage is more than 11 volts. |
| • | The engine run time is at least 17 minutes. |
| • | The secondary AIR system is inactive. |
| • | The secondary AIR system diagnostic is not running. |
| • | The short term fuel trim at the beginning of the test is greater than -5 percent. |
Conditions for Setting the DTC
The vacuum in the EVAP system decays at too fast a rate during the diagnostic test.
Action Taken When the DTC Sets
The ECM illuminates the Malfunction Indicator Lamp (MIL) and records the operating conditions in the Freeze Frame on the second consecutive drive trip that the diagnostic runs and fails.
Conditions for Clearing the MIL/DTC
| • | The ECM turns OFF the MIL after three consecutive drive trips that the diagnostic runs and passes. |
| • | A History DTC clears after forty consecutive warm-up cycles in which no failures are reported by this diagnostic or any other emission related diagnostic. |
| • | The ECM battery voltage is interrupted. |
| • | The scan tool clears the MIL/DTC. |
Diagnostic Aids
The fuel tank assembly consists of an inner fuel tank, EVAP canister, ORVR system and the associated plumbing all encased within an outer fuel tank housing. The outer housing contains a tube that allows air between the inner tank and the outer housing to vent. A leak in any of the internal components of the fuel tank assembly will exit this vent. The vent is located in front of the fuel tank above the fuel filter. If a leak is detected by air exiting this vent while the EVAP system is pressurized, the fuel tank assembly will require replacement. The internal components of the fuel tank assembly are not serviceable. A similar vent for the fuel tank pressure sensor is also located in front of the fuel tank. A leak from this vent while the EVAP system is pressurized indicates the fuel tank pressure sensor is leaking.
Check for the following conditions:
| • | Damaged, loose or incorrect fuel cap |
| • | Disconnected or damaged EVAP vent hose |
| • | EVAP purge valve not closing properly |
| • | EVAP vent valve not closing or not sealing when closed |
| • | Leaking fuel sender assembly O-ring |
| • | Leaking fuel tank or fuel filler neck |
| • | Inspect the purge line and valve for traces of carbon. Any carbon escaping from the canister may prevent the valve from closing properly. If traces of carbon are found, disconnect both ends of the purge line and blow out any contaminants by using the pressurized gas from the EVAP pressure/purge cart. Replace the purge valve and the canister/fuel tank. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
20.37 mm Hg (10.86 in. H2O) is the maximum value displayed on the scan tool even though the actual pressure in the system may be higher. If the pressure cannot be attained on the fuel tank pressure sensor, this indicates there may be a restriction in the purge line or a shifted sensor. These conditions are diagnosed in DTC P0455.
-
Inspect the purge valve and lines for traces of carbon. Carbon escaping from the canister may prevent the valve from closing properly. If this condition is found, disconnect both ends of the purge line and blow out any contaminants using the pressurized gas from the J41750 EVAP pressure/purge cart. Replace the purge valve and the canister/fuel tank.
Step | Action | Values | Yes | No | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||||||||||
2 | Is DTC P0443, P0446, P0450 or a P0455 also set? | -- | Go to the applicable DTC table | |||||||||||||||
3 |
Did you find and correct a problem? | -- | ||||||||||||||||
4 |
Is the Fuel Tank Pressure within the specified value? | -1.87 to +1.87 mm Hg (-1 to +1 in. H2O) | ||||||||||||||||
5 |
Important: Before continuing with diagnosis, zero the EVAP Pressure and Vacuum gauges on J 41750 EVAP pressure/purge cart (refer to the tool operating instructions).
Does the pressure drop below the second value within 2 minutes? | 28.02 mm Hg (15 in. H2O) 18.68 mm Hg (10 in. H2O) | ||||||||||||||||
Is the fuel tank pressure at or above the second specified value? | 20.55 mm Hg (11 in. H2O) 18.68 mm Hg (10 in. H2O) | Go to Diagnostic Aids | Go to DTC P0455 Evaporative Emission (EVAP) System Leak Detected | |||||||||||||||
7 |
Does the pressure drop below the second value within 2 minutes? | 28.02 mm Hg (15 in. H2O) 18.68 mm Hg (10 in. H2O) | ||||||||||||||||
8 |
Does the pressure drop below the second value within 2 minutes? | 28.02 mm Hg (15 in. H2O) 18.68 mm Hg (10 in. H2O) | ||||||||||||||||
9 |
Is the action complete? | -- | -- | |||||||||||||||
Replace the Purge valve. Refer to Evaporative Emission Canister Purge Solenoid Valve Replacement . Is the action complete? | -- | -- | ||||||||||||||||
11 | Replace the Vent valve. Refer to Evaporative Emission Vent Valve Replacement . Is the action complete? | -- | -- | |||||||||||||||
12 |
Does the pressure drop below the second value within 2 minutes? | 28.02 mm Hg (15 in. H2O) 18.68 mm Hg (10 in. H2O) | ||||||||||||||||
13 |
Does the scan tool indicate the Diagnostic Passed? | -- | ||||||||||||||||
14 | Does the scan tool display any additional, undiagnosed DTCs? | -- | Go to the applicable DTC table | System OK |
