Advanced Diagnostics
Advanced Diagnostics - DTC P0456: Evaporative Emission (EVAP) System Very Small Leak Detected
General Description
The evaporative emission (EVAP) leak detection system uses an engine off natural vacuum (EONV) method. The EONV method detects leakage from the change in fuel tank pressure via the fuel tank pressure (FTP) sensor with the engine off.
Here is an overview of the malfunction detection for the EONV method: Judgment 1: Judgment of detection of 0.09 inch leak as normal operation Judgment 2: Judgment of detection of 0.02 inch leak as normal operation Judgment 3: Detection of 0.02 inch leak
Judgment 4: Detection of atmospheric pressure failure
Judgment 5: Flickering of the FTP sensor
[Judgments 1, 2, and 3 happen at the same time. Judgments 4 and 5 happen at the same time.]
Judgment 1:
After the engine has stopped, the powertrain control module (PCM) monitors the variation of the FTP sensor output to detect "no 0.09 inch leak" depending on the variation of the pressure inside the fuel tank.
- If the variation of the pressure is a specified value and continues for a specified duration, it is identified as a "0.09 inch leak" and the diagnosis completes.
- If the variation of the pressure is a specified value before a specified duration has passed, it is defined as "no 0.09 inch leak", the judgment of detection of a 0.09 inch leak is completed, and it goes to 0.02 inch leak monitor.
Judgment 2:
After the engine has stopped, the PCM monitors the variation of the FTP sensor output to detect "no 0.02 inch leak" depending on the variation corresponding to the increasing pressure inside the fuel tank.
- If "no 0.02 inch leak" is detected, it is identified as normal; the diagnosis is complete.
- If the pressure inside the fuel tank does not increase a specified value within a specified duration, it goes to Judgment 3.
Judgment 3:
The PCM continues to monitor the FTP sensor output to detect "no 0.02 inch leak" depending on the variation corresponding to the decreasing pressure inside the fuel tank until the detection completes.
- If a "0.02 inch leak" is detected, it is identified as a malfunction; the diagnosis is complete.
- If "no leakage" is detected, it is identified as normal; the diagnosis is complete.
- If the pressure is not atmospheric pressure or less when the detection is completed, that data is stored and the diagnosis is complete.
Judgment 4:
After the engine has stopped, the PCM monitors the variation of the FTP sensor output to detect atmospheric pressure, after keeping the canister vent opened for a specified duration to stabilize the pressure inside the fuel tank.
- If the pressure inside the fuel tank after a specified duration has not reached a specified value from the sensor zero point, a canister vent blockage is detected.
Judgment 5:
After the engine has stopped, the PCM monitors the variation of the FTP sensor output to detect FTP sensor electrical noise failure, after keeping the canister vent opened for a specified time to stabilize the pressure inside the fuel tank.
- If the difference of pressure inside the fuel tank and an average value after a specified duration has exceeded a specified value for a specified duration, an FTP sensor electrical noise failure is detected.
Monitor Execution, Sequence, Duration, DTC Type, OBD Status
Enable Conditions
Malfunction Threshold
- The misalignment of zero point pressure inside the fuel tank is 0.7 kPa (0.2 inHg, 5 mmHg) or more.
- The output from the FTP sensor flickering is 3.1 seconds or more.
- The change rate of the pressure rise slope inside the fuel tank is 2.8 or more.
- The change rate of the pressure descending slope inside the fuel tank is 0.8 or more.
- The barometric pressure is stable for at least 29 minutes, 58 seconds.
Confirmation Procedure with the HDS
Do the EVAP FUNCTION TEST in the INSPECTION MENU with the HDS.
Driving Pattern
1. After the vehicle has been left for an appropriate amount of time as specified, with the engine coolant temperature and intake air temperature within the specified range, start the engine.
2. Warm up the engine at idle until the radiator fan comes on.
3. Drive the vehicle immediately at a speed between 45 - 75 mph (72 - 120 km/h) for at least 20 minutes.
4. After stopping the vehicle, turn the ignition switch to LOCK (0), or press the engine start/stop button to select the OFF mode, and leave the vehicle in this condition for at least 42 minutes (EONV executes).
- Drive the vehicle in this manner only if the traffic regulations and ambient conditions allow.
Diagnosis Details
Conditions for setting the DTC
When a malfunction is detected during the first drive cycle with the engine coolant temperature and intake air temperature at engine start-up within the specified temperature range, a Pending DTC is stored in the PCM memory. If the malfunction returns in the next (second) drive cycle with the engine coolant temperature and intake air temperature at engine start-up within the specified temperature range, the MIL comes on and a Confirmed DTC and the freeze data are stored.
Conditions for clearing the DTC
The MIL is cleared if the malfunction does not return in three consecutive trips in which the diagnostic runs. The MIL, the Pending DTC, the Confirmed DTC, and the freeze data can be cleared with the scan tool Clear command or by disconnecting the battery.