Leak Diagnosis, Improved Version (Certain Markets Only)
Leak diagnosis, improved version (certain markets only)
Leak diagnostics, improved version
All gases that evaporate from fuel in the fuel tank must be led to and stored in the evaporative emission system (EVAP) canister so that they can be directed into the engine for combustion. In order to detect leakages which cause evaporation of gases into the air, the fuel tank system is diagnosed for leakage. The fuel tank system consists of:
- fuel tank
- Canister purge (CP) valve (1)
- EVAP canister (2)
- leak diagnostic unit (3)
- air cleaner (ACL) (4)
- Roll-over valve (5)
- Float Limit Vent Valve (6)
- fuel filler pipe (7)
- all lines between the above components.
The fuel tank system has a leak diagnostic unit to diagnose any leakage. The leak diagnostic unit pressurizes the fuel tank system when the conditions for diagnosis have been met. The control module can detect faults in the function of the leak diagnostic unit and leakage that is 0.5 mm or greater. Minor leak; leakage greater than 0.5 mm but less than 1.0 mm. Major leak; leakage greater than 1.0 mm.
The leakage diagnostic consists of a pump and a valve that control the flow in the unit. Engine control module (ECM) checks sealing in the tank system by measuring the relationship between obtained pressure and flow from the leakage diagnostic pump when pressurized.
If a certain pressure is not obtained with a pre-determined (with known mass) the Engine control module (ECM) interprets it as a leakage from the fuel tank system.
Leakage diagnostics start in normal operation when specific conditions have been fulfilled, see below. Diagnostics can also be started by command using VIDA when you disregard some of these conditions.
Conditions for diagnosis
The diagnosis begins when all the following conditions are met:
Note! Slightly different conditions apply when diagnostics are started by command using VIDA. See relevant information about these, available together with Quick-test tank system.
- No diagnostic trouble codes for EVAP-valve or atmospheric pressure sensor may be stored.
- The engine is switched off until the engine coolant temperature (ECT) has fallen to a few degrees above the outside temperature, then engine running for at least 10 minutes.
- Ignition off
- Vehicle speed 0 km/h
- Engine temperature 4-35 °C.
- Maximum altitude of 2500 meters above sea level.
- Outdoor temperature between 4-35 °C.
- Fuel volume in the tank between 0-85%. The engine control module (ECM) ignores these parameters if a diagnostic trouble code (DTC) is stored for the fuel level sensor and the fuel volume cannot be determined.
- Battery voltage between 11-15 V. The voltage must be stable.
- EVAP canister purge valve closed
- Low volume in the canister.
- Tank hatch locked.
Note! Locking occurs when the vehicle speed exceeds 20 km/h.
Diagnostic phases
The diagnostic is divided into the following phases and is carried out in sequence when all conditions for the diagnostic have been met.
- reference phase
- function test
- checking tank system.
Reference phase
Before leakage diagnosis itself can be started, the control module performs a reference phase for leakage. Reference phase for leakage which is 0.5 mm is performed by the leakage diagnostic unit's pump pumping ambient air through a hole which is 0.5 mm and back out to the ambient air. During that time, the pump is monitored in the leakage diagnostic unit and reference values are stored away for later use in assessing the tank system's sealing.
If any reference value for the pump is unreasonably high or low, or varies too much, then diagnosis is interrupted and a diagnostic trouble code is generated.
Function test
After the reference phase, the leakage diagnostic unit's valve is activated and the air flow is controlled to the tank system to pressurize the tank system. This shift in air flow means that the pump load drops briefly before the pressure builds up in the tank system. If the load does not change within reasonable limits within reasonable time, then diagnosis is interrupted and a diagnostic trouble code is generated.
Checking tank system, major leakage (leakage bigger than 1.0 mm)
Diagnosis are performed every time conditions for diagnosis are fulfilled.
The leakage diagnostic unit pressurizes the tank system and checks sealing by monitoring the pressure in the tank system. The pressure is a calculated pressure, calculated using measured power consumption on the pump. If the pressure stabilizes and/or does not go above 1500 Pa within 450 seconds, this is interpreted as a leakage from the fuel tank system. Diagnosis is interrupted and a diagnostic trouble code for major leakage is generated.
Checking tank system, minor leakage (leakage bigger than 0.5 mm but smaller than 1.0 mm)
Diagnosis for minor leakage is performed every other time conditions for diagnosis are fulfilled. Otherwise, diagnosis finishes after checking for major leakage.
The leakage diagnosis unit continues pressurizing the tank system. Engine control module (ECM) checks sealing in the tank system by measuring the relationship between reached pressure and flow from the leakage diagnosis pump when pressurizing. In a sealed system the relationship between these shall be linear. Any deviations from the linear relationship is calculated and used to assess the tank system's sealing.
If the assessment, performed within 15 minutes, is that a minor leakage has been detected in the tank system, a diagnostic trouble code for minor leakage is generated.