Leak diagnostics, original version (-2004)
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 that cause gas to evaporate into the air, the fuel tank system is diagnosed for leakage. The fuel tank system consists of fuel tank, , fuel filler pipe (7), EVAP canister (2), EVAP valve (1), air cleaner (4), leak diagnostic unit (3) and all cables between these components. The fuel tank system has a leak diagnostic unit that makes it possible to diagnose any leaks. The unit pressurizes the fuel tank system when the ignition is switched off if the conditions for leak diagnostics are met. The control module can detect faults in the function of the diagnostic unit and leakage that is 0.5 mm (minor leak) or greater (major leak, fuel filler cap missing).
The leak diagnostic unit consists of a pump and a valve that controls the air flow in the unit. The fuel tank system tests for leaks by measuring the power consumption of the pump. The power consumption of the pump corresponds to a certain pressure in the fuel tank system. During diagnosis, the rate at which the pressure can build up is checked, taking into account the quantity of fuel in the tank. The quicker the pressurization the better the fuel tank system is sealed.
Conditions for diagnosis
The diagnosis begins when all the following conditions are met:
- There must be no diagnostic trouble code (DTC) stored for the following components or functions:
- the power stage for the pump in the leak diagnostic unit
- the power stage for the valve in the leak diagnostic unit
- the power stage for the EVAP canister purge valve
- the EVAP canister purge valve.
- Engine off for at least 5 hours (context), engine running for at least 20 minutes (context)
- Ignition off
- Vehicle speed 0 km/h
- Engine coolant temperature (ECT) +4 °C or higher
- Maximum altitude of 2500 meters above sea level
- Outside temperature between +4 and +35 °C
- Stable signal from the fuel level sensor
- Fuel volume in the tank between 15-85 %
- Battery voltage between 11.0-14.5 V. The voltage must be stable
- EVAP canister purge valve closed
- Low volume in the canister.
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 1
- Function test
- Leak diagnostic.
Reference phase and function test
(the illustration is a diagram of a fault free fuel tank system) Before the actual leak diagnostic begins, the control module enters a reference phase for leakage and checks the components in the system.
Reference phase 1 and reference phase 2
During the reference phases (1-2) for leakage that is 0.5 mm, the pump in the leak diagnostic unit pumps ambient air through a 0.5 mm hole and back out to the ambient air. At the same time, the power consumption of the pump is measured and stored in the control module (A). The stored value for the power consumption of the pump corresponds to a leakage of 0.5 mm.
Function test
If the value for the power consumption of the pump is too high or low during reference phase1 (1-2), or if the value varies too much during reference phase 1 (1-2), the diagnostic is cancelled and starts again the next time the conditions for the diagnostic are met. Diagnostic trouble code (DTC) ECM-431D, faulty signal, is stored if the diagnostic is cancelled 10 times due to excessive variation in the power consumption of the pump.
After the reference phase, the valve (2) in the leak diagnostic unit is activated and controls the air flow to the fuel tank to pressurize the fuel tank system. This change of air flow will cause the power consumption of the pump to fall briefly before the pressure builds up in the fuel tank system (3). Diagnostic trouble code (DTC) ECM-431D, signal missing, is stored if the value for the power consumption of the pump drops too quickly, too slowly or not at all.
Leak diagnostic
(the illustration is a diagram of a fault free fuel tank system). As long as diagnostic trouble code (DTC) ECM-431D is not stored, the leak diagnostic will be carried out after the reference phase and the function test.
Major leak
(leaks >1.0 mm) The diagnostic for "major leaks" is carried out every other time when the diagnostic conditions are met. The leak diagnostic unit pressurizes the fuel tank system, measures the power consumption of the pump (4) and compares this with a calculated desired value (B). If the measured value does not reach the calculated desired value within a certain amount of time (this time is determined by the fuel level in the tank), the function of the leak diagnostic unit is rechecked by running reference phase 2 again to check that low power consumption has not led to changes in the components. Diagnostic trouble code ECM-400C, major leak, is generated if the power consumption of the pump is OK during reference phase 2.
Diagnostic trouble code (DTC) ECM-4338 (fuel tank filler cap missing) will also be stored and the driver will receive a text message in the Driver Information Module (DIM) when a major leak is detected by the Engine Control Module (ECM).
Minor leak
(leaks >0.5 mm <1.0 mm). The diagnostic for "minor leaks" is carried out every 14th time when the diagnostic conditions are met. The diagnostic for major leaks is always run before the diagnostic for minor leaks. The leak diagnostic unit continues to pressurize the fuel tank system (5). If the measured value (6) is the same or less than the value stored in the reference phase (A) after a certain amount of time (determined by the fuel level in the tank), reference phase 2 (7) is run to ensure that the lower power consumption (6) is not the result of changes in components. If the measured power consumption during the second reference phase (7) is lower than that measured during pressurization (6), the control module interprets this as meaning that the fuel tank system is sealed. Diagnostic trouble code ECM-400C, minor leak, is generated if the measured power consumption from the second reference phase (7) is the same or higher than that measured during pressurization (6).