P0456

DTC P0456: Evaporative Emission (EVAP) System Very Small Leak Detected

System Description
The Evaporative emission (EVAP) system includes the following components:
- Fuel tank
- EVAP emission vent solenoid
- Fuel tank pressure sensor
- Fuel pipes and hoses
- Fuel vapor lines
- Fuel cap
- EVAP emission canister
- Purge lines
- EVAP emission canister purge valve
- EVAP emission service port

The EVAP emission system is checked by applying vacuum to the EVAP emission system and monitoring for a vacuum decay. The Engine Control Module (ECM) monitors the vacuum level through the fuel tank pressure sensor signal.

At the appropriate time, the EVAP canister purge valve and the EVAP vent solenoid are turned ON, allowing the engine to draw a small vacuum on the entire evaporative emission system. After the desired vacuum level has been achieved, the EVAP canister purge valve is turned OFF, sealing the system. A leak is detected by monitoring for a decrease in the vacuum level over a given time period, when all other variables remain constant. A small leak in the system will cause Diagnostic Trouble Code (DTC) P0456 to be set.

Conditions for Setting the DTC
No relevant DTCs are set.

(Common EVAP Enable Criteria)
- System voltage is between 10 and 16 V.
- Barometric Pressure (BARO) is greater than 72 kPa (10.4 psi).
- Engine soak time is greater than 720 minutes. Or, at startup IAT - ECT is less than 12 °C 53.6 °F).
- At start up, Engine Coolant Temperature (ECT) and Intake Air Temperature (IAT) are between 0 °C (32 °F) and 40 °C (104 °F).
- Startup IAT - IAT is less than 3 °C (5.4 °F).
- Purge enable time is less than pre-determined value based on startup ECT.
- Fuel level is between 6% and 93%.
- Engine run time is between 1 second and 300 seconds plus purge enable time.

(Small Leak Enable Criteria)
- When idling, engine speed is less than 1,500 rpm, vehicle speed is less than 3 km/h, throttle position is less than 1%.
- When creeping, engine speed is less than 1,500 rpm, vehicle speed is less than 6 km/h, throttle position is less than 2%, change in MAP is less than 10 kPa.

Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- The PCM/ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.
- A history DTC is stored.

Conditions for Clearing the MIL/DTC
- The MIL will turn OFF after four consecutive ignition cycles in which the diagnostic runs without a fault.
- A history DTC will clear after 40 consecutive warm up cycles without a fault.
- The DTC(s) can be cleared using the scan tool.

Diagnostic Aids
Whenever this diagnostic reports the system has passed, or if the battery is disconnected, the diagnostic must fail on consecutive tries before setting a DTC. The initial failure is not reported to the diagnostic executive or displayed on a scan tool. A passing system always reports
to the diagnostic executive immediately.
Check for the following conditions:
- Missing or damaged O-rings at fuel vapor and EVAP emission purge line canister fittings
- Cracked or punctured EVAP emission canister
- Damaged source vacuum line, EVAP emission purge line, EVAP emission vent hose or fuel tank vapor line.
- Poor connection at ECM. Inspect harness connectors for the following conditions:
- Backed-out terminals
- Improper mating
- Broken locks
- Improperly formed
- Damaged terminals
- Poor terminal-to-wire connection

- Damaged harness. Inspect the wiring harness to the EVAP emission vent solenoid, EVAP emission canister purge valve and the fuel tank pressure sensor for an intermittent open or short circuit.

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
1. The On-Board Diagnostic (OBD II) System Check prompts the technician to complete some basic checks and to store the Freeze Frame and Failure Records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred.
The information is then stored on the scan tool for later reference.
2. If a vent solenoid or EVAP canister purge valve electrical malfunction is present, the purge system will not operate correctly. Repairing the electrical malfunction will very likely correct the condition that set DTC P0456.
3. Checks the fuel tank pressure sensor at ambient pressure.
4. Forces fuel tank pressure sensor to re-zero.
5. Verifies that the fuel tank pressure sensor accurately reacts to EVAP system pressure changes.

Step 1-3:

Step 4-11:

Step 12-13:

Troubleshooting