P0456 (U5/Low Emissions)
DTC P0456 - EVAPORATIVE EMISSION CONTROL SYSTEM LEAK DETECTED (VERY SMALL LEAK)OUTLINE OF DIAGNOSIS
In this system diagnosis, checking for leakage and valve function is conducted by changing the fuel tank pressure with each solenoid valve switched to ON/OFF, and monitoring the pressure change using the fuel tank pressure sensor. 0.04-inch diagnosis is performed in the order of mode Z, mode A, mode B, mode C and mode D, and 0.02-inch diagnosis is performed in the order of mode Y, mode A, mode B, mode C and mode D.
- 0.04-inch Diagnosis
- 0.02-inch Diagnosis
- Mode Table for Evaporative Emission Control System Diagnosis
COMPONENT DESCRIPTION
- Pressure Control Solenoid Valve
PCV controls the fuel tank pressure to be equal to the atmospheric air pressure.
Normally, the solenoid is set to OFF. And the valve opens and closes mechanically in accordance with the pressure difference between tank and atmospheric air, or tank and canister.
The valve is forcibly opened by setting the solenoid to ON at the time of diagnosis.
- Valve Operation and Air Flow
In the figure shown, divided by the diaphragm, the part above X is charged with atmospheric air pressure, and the part below X is charged with tank pressure. Also, the part above Y is charged with tank pressure, and the part below Y is charged with canister pressure.
If the atmospheric air pressure port is A, tank pressure port is B, and canister pressure port is C, the air flows according to pressure difference from each port as shown in the table.
- When A < B (Solenoid OFF)
- When B < C (Solenoid OFF)
- When Solenoid is ON
- CCV
CCV controls the ambient air to be introduced to the canister.
- Tank Pressure Switching Solenoid
One of the atmospheric pressure switching solenoid valves is connected to fuel tank pressure sensor and the other is released to atmosphere. The passage to fuel tank pressure sensor is usually released to atmosphere because the solenoid is set to OFF, but the solenoid is set to ON at diagnosis and the passage open to atmosphere can be closed.
- Purpose of this solenoid
Fuel tank pressure sensor detects the difference between the atmospheric air pressure and the tank pressure and the ECM monitors the pressure difference.
Even if the tank pressure is constant, the atmospheric air pressure varies depending on the driving height, and the pressure signal transmitted to ECM will change.
Especially, in the small leakage [0.5 mm (0.02 in)], minute change in the tank pressure has to be detected. This diagnosis period is long (approx. 29 seconds). And if the driving height changes during the diagnosis, the atmospheric air pressure changes. In this case, it becomes difficult to precisely detect the tank pressure variation, causing erroneous diagnosis. Therefore, using the atmospheric pressure switching solenoid, atmospheric air is sealed between the fuel tank pressure sensor and atmospheric pressure switching solenoid, maintaining the air pressure constant and enabling the detection of minute variation of tank pressure.
NOTE: ECM also has the atmospheric air pressure sensor, and always monitors atmospheric air. However, as the monitoring range is large, that is, 53 to 107 kPa (400 to 800 mmHg, 16 to 32 inHg) it is not suitable for detection of minute pressure variation.
In the case of small leakage diagnosis, the tank pressure variation is very small, that is, 0.13 to 0.27 kPa (1 to 2 mmHg, 0.04 to 0.08 inHg) and the fuel tank pressure sensor is equipped.
ENABLE CONDITION
GENERAL DRIVING CYCLE
- 0.04-inch Diagnosis
- Perform the diagnosis only once in more than 856 seconds after the engine start at the constant driving speed of 32 km/h (20 MPH) or more.
- Pay attention to the fuel temperature and fuel level.
- 0.02-inch Diagnosis
- Perform diagnosis in more than 335 seconds after engine start at the constant speed of 68 km/h (42 MPH) or more, and judged OK or NG.
- If not judged OK or NG, repeat the diagnosis.
- Pay attention to the fuel temperature and fuel level.
DIAGNOSTIC METHOD
- MODE Z (Purge control solenoid valve open malfunction diagnosis, CPC close malfunction diagnosis)
DTC P0457
- Purpose of Mode Z
When performing the leakage diagnosis of EVAP system, CPC has to operate normally. Therefore, mode Z is used to diagnose the CPC open fixation.
If the CPC open fixation trouble is detected, the EVAP system leakage diagnosis is cancelled.
- DIAGNOSTIC METHOD
CPC open fixation diagnosis are performed in mode Z as shown in the figure.
- Diagnosing function of CPC [P0457]
CPC functional diagnosis is performed by monitoring the tank pressure in Mode Z.
Normality Judgment
Make OK judgment in 3 seconds after Mode Z started, and change to Mode A if OK.
- Normal Operation
- evptez - evptezha <= 0.4 kPa (3.0 mmHg, 0.12 inHg)
Judge normal when calculation is completed.
Abnormality Judgment
If OK judgment cannot be made, extend Mode Z 16 seconds more, and judge NG when all the criteria are completed in 16 seconds.
Finish the Evap. diagnosis when making NG judgment for purge control solenoid valve open fixation.
Cancel the Evap. diagnosis when the OK/NG judgment for drain valve close fixation and purge control solenoid valve open fixation cannot be made in Mode Z.
- Purge Control Solenoid Valve Open Fixation
- evptezini <= 1.43 kPa (10.7 mmHg, 0.42 inHg)
- No fuel rolling of above 2 L (0.79 US gal, 0.67 Imp gal) for more than 40 seconds.
Judge normal when these calculations are completed.
- Leak Diagnosis
DTC P0442
DTC P0456
DTC P0457
- DIAGNOSTIC METHOD
- The diagnostic method consists of creating a sealed vacuum in the fuel tank and then determining the presence of leakage from the speed at which the tank internal pressure returns to atmospheric pressure.
- The diagnosis is divided into the following five phases.
Mode A: (Estimation of evaporation gas yield)
The amount of change of tank pressure (P1) in Mode A is calculated. After calculating P1, change to Mode B.
Mode B: (Seal negative pressure)
Introduce the negative pressure in the intake manifold to the tank.
Approx. 0 -> -1.4 kPa (0 -> -10.5 mmHg, 0 -> -0.41 inHg) (0.04-in diagnosis)
Approx. 0 -> -3.05 kPa (0 -> -22.9 mmHg, 0 -> -0.9 inHg) (0.02-in diagnosis)
When the pressure above (desired negative pressure) is reached, Mode C is entered.
In this case, if the tank pressure does not become the desired negative pressure, judge that there is a large leakage in the system.
Judge NG when the malfunction criteria is completed.
Finish the Evap. diagnosis when judging large leak (10 seconds) in 0.04-inch diagnosis. Cancel the diagnosis (14 seconds) in 0.02-inch diagnosis.
Abnormality Judgment
Judge NG (large leak) when the criteria are completed in the specified time.
Mode C: (Check increasing pressure)
Stop the introduction of negative pressure. (Wait until the tank pressure returns to the start level of P2 calculation.)
Change to Mode D when the tank pressure returns to the start level of P2 calculation.
Judge immediate OK and change to Mode E when it does not return in spite of spending the specified time.
Mode D: (Measurement of negative pressure changes)
Monitor the pressure variation in the tank in Mode Z. In this case, the tank pressure increases, that is, the pressure becomes as high as the atmospheric air pressure, because evaporator is generated. However, if any leakage exists, the pressure increases additionally in proportion to this leakage. The pressure variation of this tank is P2.
After calculating P2, perform following small leak diagnosis.
- After Mode D
Assigning P1 and P2, which are tank variations measured in Mode A and Mode B, to the formula below, judge the small leakage of the system. If the measured judgment value exceeds the threshold value, it is judged to be malfunction.
- 0.04-inch Diagnosis
Abnormality Judgment
Judge NG when the criteria are completed and judge OK when not completed.
- 0.02-inch Diagnosis
Abnormality Judgment
Judge NG when the criteria are completed.
Normality Judgment
Judge OK when the criteria are completed.
DTC CLEAR CONDITION
- When the OK idling cycle was completed 40 times in a row
- When "Clear Memory" was performed
MALFUNCTION INDICATOR LIGHT CLEAR CONDITION
- When the OK driving cycle was completed 3 times in a row
- When "Clear Memory" was performed
FAIL SAFE
None
ECM OPERATION AT DTC SETTING
- Memorize the freeze frame data. (For test mode $02)
- Memorize the diagnostic value and trouble standard value. (For test mode $06)