System Description
When running the DTC P0456 Evaporative Emission (EVAP) System Very Small Leak Detected diagnostic detects evaporative emission system leaks as small as 0.51 mm (0.020 inch). The powertrain control module (PCM) will command the EVAP vent valve ON, CLOSED, and the purge valve and the vacuum pressure switching valve ON, OPEN, with the engine running. This allows engine vacuum into the EVAP system. The PCM then commands the purge valve OFF, CLOSED, sealing the system. The PCM then monitors the fuel tank vapor pressure sensors signal to determine if there is vacuum decay. A rise or increase just above normal pressure indicates there is a small leak in the evaporative emission system. If the PCM detects the vacuum level was not achieved and vacuum decay was within a specified value a DTC P0456 will set.
Conditions for Running the DTC
| • | DTC P0441, P0446, P0450, P0451, P0452, and P0453 are not set. |
| • | The barometric pressure (BARO) indicates that the altitude is less than 2,400 meters (7,872 feet). |
| • | The battery voltage is at least 11 volts. |
| • | The fuel level is approximately 10-90 percent--no excess fuel slosh is indicated.. |
| • | The engine coolant temperature (ECT) sensor and the intake air temperature (IAT) sensor are near the same temperature at engine start. |
| • | The ECT and the IAT are between 10°C (50°F) and 32°C (89°F) at engine start. |
| • | The engine has been operating for at least 50 minutes. |
| • | The vehicle is operated at steady speeds and doesn't exceed 130 km/h (81 mph). |
| • | The vehicle speed has been more than 64 km/h (39 mph) for at least 15 seconds or less than 64 km/h (39 mph) for at least 60 seconds. |
| • | The EVAP canister purge valve has been open and the fuel tank pressure (FTP) sensor indicates a negative pressure in the fuel tank. |
| • | DTC P0456 runs once per drive cycle when the above conditions are met. |
Conditions for Setting the DTC
The EVAP system can achieve vacuum, but a vacuum decay near 0.51 mm (0.020 inch) is detected during the diagnostic test.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles in which the diagnostic runs with the fault active. |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the MIL on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present. |
| • | A DTC will clear after 40 consecutive warm-up cycles have occurred without a fault. |
| • | A DTC can be cleared by using the scan tool Clear Information function. |
Diagnostic Aids
| • | The EVAP control system is required to detect evaporative emission fuel system leaks as small as 0.020 inch, between the fuel fill cap, and the purge solenoid. |
| • | To help locate intermittent leaks, use the J 41413-200 Evaporative Emissions System Tester (EEST) to introduce smoke into the EVAP system. Move all EVAP components while observing smoke with the J 41413-SPT High Intensity White Light. |
| • | A temporary blockage in the EVAP purge solenoid, purge pipe or EVAP canister could cause an intermittent condition. Inspect and repair any restriction in the EVAP system. |
| • | In order to improve the visibility of the smoke exiting the EVAP system, observe the suspected leak area from different angles with the J 41413-SPT . |
| • | The test for leaks with smoke is performed with the system subjected to positive pressure. The trouble code diagnostic tests for a leak with vacuum or negative pressure. Perform the Purge/Seal test with the scan tool in order to test for leaks using vacuum pressure. Refer to Purge/Seal Function in Service Bay Test. If the Purge/Seal test fails, inspect the EVAP system o-ring seals for failure. O-ring seals can provide a good seal with pressure applied in one direction, but leak when the pressure is applied in the opposite direction. |
| • | Operating the vehicle in Check Mode will increase the ability of the powertrain control (PCM) module to detect engine control system malfunctions. Refer to Check Mode in Service Bay Test. |
| • | Reviewing the Freeze Frame Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition. |
| • | For intermittent conditions refer to Intermittent Conditions. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step verifies that the DTC P0456 is captured in the freeze frame/failure record list. When multiple EVAP system DTCs are set, the DTC stored in the freeze frame/failure record is the preferred diagnostic starting point.
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The fuel filler pipe has two vent lines that allow for recirculation of fuel vapors between the fuel filler pipe and the fuel tank. Because of these vent lines the EEST can be connected to the EVAP service port for leak detection. Waiting until smoke is seen before plugging the EVAP canister drain hose speeds up the filling of the canister with smoke. Introducing smoke in between 60 second intervals of Nitrogen will speed up the filling of smoke in the fuel tank and filler pipe vapor space. This occurs because the pressure at which Nitrogen gas is applied is greater than the pressure at which smoke is introduced. The Nitrogen gas pushes the smoke that was just introduced through the canister and into the fuel tank. The EVAP vent solenoid DOES NOT have to be turned ON in order to test for leaks. A one way check valve located in the vent port of the EVAP canister provides containment of smoke and pressure within the EVAP system.
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This test verifies that the fuel tank pressure (FTP) sensor is accurate. An FTP sensor that does not correctly respond to vacuum, or pressure may cause this DTC to set.
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This step verifies whether a leak in the EVAP system still exists. If the flow gage on the EEST and/or the scan tool pressure reading remain constant, there is no external leak. If the EEST gage indicates flow, or the scan tool pressure reading decreases, there is still an external leak in the EVAP system.
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This step tests the fuel tank assembly for leaks with the tank removed from the vehicle. The J 41413-300 EVAP Cap and Plug Kit enables you to use smoke to test for a leak on the portions of the fuel tank that are not visible when installed in the vehicle.
Step | Action | Values | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Evaporative Emissions Hose Routing Diagram | ||||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||||
2 |
Is a DTC P0450, P0451, P0452, or P0453 present? | -- | Go to Step 3 | |||||||||||
Is DTC P0456 captured in the Freeze Frame/Failure records? | -- | Go to Step 4 | ||||||||||||
4 |
Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 5 | ||||||||||
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Important: Ensure that the vehicle underbody temperature is similar to the ambient temperature and allow the surrounding air to stabilize before starting the diagnostic procedure. System flow will be less with higher temperatures.
Did you locate and repair a leak source? | -- | Go to Step 10 | Go to Step 6 | |||||||||||
6 |
Is the FTP in H20 near the specified value? | 0.17 mm Hg (0.09 in H2O) | Go to Step 7 | Go to Step 9 | ||||||||||
Is the FTP parameter more than the second specified value? | 18.68 mm Hg (10 in H2O) 9.34 mm Hg (5 in H2O) | Go to Step 8 | Go to Step 9 | |||||||||||
8 |
Is the FTP Sensor parameter less than the specified value? | 1.86 mm Hg (1 in H2O) | Go to Step 10 | Go to Step 9 | ||||||||||
9 | Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement. Did you complete the replacement? | -- | Go to Step 12 | -- | ||||||||||
Did the flow gage indicator remain in the no flow position? | -- | Go to Step 12 | Go to Step 11 | |||||||||||
Inspect the fuel tank and component parts for leaks. Refer to Fuel Tank Leak Test. Did you find and correct a condition? | -- | Go to Step 12 | Go to Diagnostic Aids | |||||||||||
12 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||||
