Leak Diagnostics

Leak diagnostics

Overview
Vapor which evaporates from the fuel in the fuel tank is routed to and stored in the EVAP canister from where it is guided into the combustion process via the canister purge (CP) valve and negative pressure in the intake manifold. The diagnosis is designed to detect leaks between 0.5-1 mm, depending on the model year.
The tank system consists of the fuel tank, fuel tank filler cap, fuel filler pipe, roll-over valve, EVAP canister, EVAP components, fuel tank pressure sensor, and EVAP canister shut-off valve.
The diagnostic is divided into different phases under which the various components are tested and faulty components are isolated with a diagnostic trouble code (DTC).

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:
- EVAP canister shut-off valve
- the fuel tank pressure sensor
- the canister purge (CP) valve
- Vehicle speed is between 30-160km/h, must be steady driving
- Engine speed below 3500 rpm
- Engine coolant temperature (ECT)> 60°C
- Maximum altitude of 2500 meters above sea level
- Outside temperature above +3.5°C
- Stable fuel tank pressure
- Low volume in the canister.
The diagnostic test works as follows:
- 1. The canister purge (CP) valve (C) closes the fuel tank ventilation. The EVAP canister shut-off valve is still open. The pressure in the tank must now return to atmospheric pressure. If the pressure in the fuel tank does not return to atmospheric pressure, the canister purge (CP) valve (C) is leaking or that the EVAP canister shut-off valve (B) is blocked. Diagnostic trouble code (DTC) ECM-4047 canister purge (CP) valve leaking or EVAP canister shut-off valve blocked is stored
- 2. The evaporative emission system (EVAP) valve (C) is closed and the EVAP canister shut-off valve (B) closes the opening for fresh air ventilation. The pressure in the fuel tank must be unchanged or rise. If the fuel tank pressure drops the canister purge (CP) valve is leaking. Diagnostic Trouble Code (DTC) ECM-4047, canister purge (CP) valve leaking is stored. If the pressure in the fuel tank rises, there is considerable fuel evaporation and the diagnostic is cancelled
- 3-4. The EVAP canister shut-off valve (B) remains closed, the evaporative emission system (EVAP) valve (C) starts to pulse. The pressure (A) in the fuel tank now starts to drop quite quickly. If the pressure does not drop quickly there is a major leak in the system. Diagnostic trouble code (DTC) ECM-4308 leak diagnostic major leak is then stored. If the pressure drops too quickly instead, the fuel tank level is too high and the diagnostic is cancelled
- 5-6-7 The canister purge (CP) valve (C) closes. The EVAP canister shut-off valve (B) remains closed. When the fuel tank pressure has stabilized, a check is carried out as to whether pressure is rising too quickly in the fuel tank. This would indicate a minor leak in the fuel tank system and ECM-4308 Minor leak would be stored
- 8-9-10. The evaporative emission system (EVAP) valve (C) pulses, so that the fuel tank pressure (A) drops again. The EVAP canister shut-off valve (B) then opens so that the fuel tank pressure can return to atmospheric pressure. Diagnostic trouble code (DTC) ECM-4047 EVAP canister shut-off valve blocked is stored if the recovery time is too long. The time taken to return to atmospheric pressure is also a measurement of the amount of fuel in the tank. The fuel level is used as a compensation value when calculating the size of the leak during stages 5-6-7 above.
The diagnostic test starts at the earliest 13 minutes after the engine has started when all conditions have been fulfilled, and takes approximately 60-80 seconds. If the diagnostic is interrupted it will try again when all the conditions have been fulfilled again. The control module makes a maximum of 20 attempts in one trip. No more attempts are made until the engine is started again.