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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 a vacuum-retention (decompression) method and an engine off natural vacuum (EONV) method. This method detects leakage by monitoring the vacuum-retention ability of the EVAP system (from EVAP canister purge valve to fuel tank). 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 0: Judgement of detection of 0.09 inch leak as normal operation
Step 1: Judgement of detection of 0.02 inch leak as normal operation
Step 2: Detection of 0.02 inch leak

Step 0:
Once required conditions for the monitor are met, the engine control module (ECM)/powertrain control module (PCM) applies vacuum to the EVAP system line from the purge control solenoid (PCS) valve through the fuel tank, and monitors the variation of the FTP sensor output to detect a "0.09 inch leak".

- If a "0.09 inch leak" is detected, it is identified as a malfunction; the diagnosis is complete.
- If "no 0.09 inch leak" is detected, the ECM/PCM goes to step 1, judgement of detection of a 0.02 inch leak as normal operation .
- If sufficient vacuum cannot be drawn on the EVAP system line, it is identified as either "EVAP system low purge flow (P0497)" or "EVAP system leak detected fuel fill cap loose/off (P0457)" (refer to the applicable DTC detail).

Step 1:
After the engine has stopped, the ECM/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 "no 0.02 inch leak" is not detected, the ECM/PCM goes to step 2, detection of a 0.02 inch leak .

Step 2:
The ECM/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.

- 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.




Monitor Execution, Sequence, Duration, DTC Type, OBD Status




Enable Conditions

Malfunction Threshold
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 20 minutes.

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 32 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 ECM/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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