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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: Step 1: Judgement of detection of 0.09 inch leak as normal operation
Step 2: Judgement of detection of 0.02 inch leak as normal operation
Step 3: Detection of 0.02 inch leak
Step 4: Detection of atmospheric air open failure
Step 5: Flickering of the FTP sensor
[Step 1, 2 and 3 proceed simultaneously. Step 4 and 5 proceed simultaneously.]

Step1: 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 corresponding to the pressure inside the fuel tank.
- If the variation corresponding to the pressure is less than a specified value and continues for a specified duration, it is identified as a malfunction of "0.09 inch leak" and the diagnosis completes.
- If the variation corresponding to pressure is more than a specified value before a specified duration has passed, it is defined as "no 0.09 inch leak", judgement of detection of a 0.09 inch leak is completed, and goes to 0.02 inch leak monitor.

Step 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 for a specified value or more within a specified duration, goes to step 3.

Step 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, reserve identification and the diagnosis is complete.

Step 4: After the engine has stopped, the PCM monitors the variation of the FTP sensor output to detect atmospheric air failure, 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 passed deviated exceeding a specified value from the sensor zero point, and if oil is not identified to fuel during EONV is performed, atmospheric air open failure is detected.

Step 5: After the engine has stopped, the PCM monitors the variation of the FTP sensor output to detect FTP sensor flickering failure, after keeping the canister vent opened for a specified duration to stabilize the pressure inside the fuel tank.
- If the deviation of pressure inside the fuel tank and an average value after a specified duration has passed exceeded a specified value for more than a specified duration, failure of FTP sensor flickering 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 0.6 kPa (0.1 in.Hg, 5 mmHg) or more.
- The output from the FTP sensor flickering is 3 seconds or more.
- The variation of pressure inside the fuel tank after phase 1 is 0.3 kPa (0.1 in.Hg, 2.8 mmHg) or more (depending on fuel level and barometric pressure).
- The sum of the variations of pressure inside the fuel tank after phase 1 and phase 2 is 10 kPa (3.1 in.Hg, 80 mmHg) or less (depending on fuel level and barometric pressure).
- The barometric pressure is stable for at least 24 minutes, 55 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 engine, turn the ignition switch off, and leave the vehicle for 37 minutes or more (EONV executes).

- Drive the vehicle in this manner only if the traffic regulations and ambient conditions allow.

Diagnosis Details

Conditions for illuminating the MIL
When a malfunction is detected during the first drive cycle with the ECT and IAT at engine start-up within the specified temperature range, a Temporary DTC is stored in the PCM memory. If the malfunction recurs during the next (second) drive cycle with the ECT and IAT at engine start-up within the specified temperature range, the MIL comes on and the DTC and the freeze frame data are stored.

Conditions for clearing the MIL
The MIL will be cleared if the malfunction does not recur during three consecutive trips in which the diagnostic runs.

The MIL, the DTC, the Temporary DTC, and the freeze frame data can be cleared by using the scan tool Clear command or by disconnecting the battery.
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