EVAP System Diagnostic Leak Test, Performing

EVAP System Diagnostic Leak Test, Performing

Observe safety precautions => [ Safety Precautions ] Safety Precautions.

Observe rules for cleanliness => [ Clean Working Conditions ] Clean Working Conditions.

Function

The evaporative emissions (EVAP) system, diagnostic leak test recognizes leaks in the entire fuel system including the fuel tank, Evaporative Emission (EVAP) canister and Evaporative Emission (EVAP) Canister Purge Regulator Valve (N80).

On the mechanical side, the leak detection system consists primarily of a vacuum activated diaphragm pump with a reed contact on an activating rod at the pump diaphragm. The pump is supplied its vacuum via the engine intake.

• When diagnostic leak test is activated, the Leak Detection Pump (LDP) increases pressure in the fuel system to 20 to 30 mbar. The pump membrane is then expanded so that the reed contact at the operating rod remains in the "open" position.

• The diagnostic will test whether the reed contact remains open within 10 seconds. Then the fuel system is leak-free.

• If pressure falls (indicating a leak), the diaphragm moves and the reed contact closes.

• If reed contact closes within 10 seconds of leak detection time, perform a further test:If this is the case, the membrane pump will pump 4 additional strokes. The Engine Control Module (ECM) measures the time between these 4 strokes and closure of the reed contact. From that, the control module recognizes a "small leak" (greater than 1 mm in diameter) or a "large leak".

Leak diagnostic is activated automatically shortly following every engine start. If a malfunction is recognized, a DTC entry follows. The Malfunction Indicator Lamp (MIL) in the instrument cluster will light up if the malfunction is recognized for two subsequent starts.

With engine running, Engine Control Module (ECM) performs a diagnostic leak test automatically in certain intervals.

• Secure all hose connections using hose clamps appropriate for the model type.

• Always replace seals and gaskets.

Function Test

- Start engine and let it run 15 minutes at idle.

- Select measuring value "Test-ID 01: Tank leak test" and check whether specified value is being reached => [ Diagnostic Mode 08 - Request Control of On-Board System, Test or Component ] Diagnostic Modes 01 - 09, Diagnostic mode 8: Tank leak test.

- Check specified value of tank leak test at idle.

Specified value: Test OK

• The function test can take a few minutes.

• If the accelerator pedal is depressed during the test, the test will be aborted.

• To repeat the tank leak test, switch ignition off and start engine again and let run at idle.

- End diagnosis and switch ignition off.

If specified value is not reached, check tank system for proper seal.

Fuel Supply and Ventilation Systems, Checking for Leaks

• The following describes areas in the fuel supply and ventilation systems that should be checked for possible leaks. After making necessary repairs, perform leak test again to ensure that all leaks were successfully repaired.

- Switch ignition off.

- Check whether fuel filler cap was completely closed for test.

- Check whether seal of fuel filler cap is damaged or pinched and must be replaced.

- Remove luggage compartment floor lining.

- Remove covers for connector flange on left and right sides.

• Observe installation notes for connector flange.

- Check whether seals under connector flanges are OK and locking rings are properly tightened on fuel tank. Also check fuel line connections.

- Visually check all lines and hose connections of fuel supply system and replace leaking lines, e.g.:

Line from EVAP canister to Evaporative Emission (EVAP) Canister Purge Regulator Valve (N80) (in engine compartment)

Lines from EVAP canister to Leak detection pump (LDP) (V144).

Line from fuel tank to Evaporative Emission (EVAP) canister (under cover for EVAP canister)

Fuel lines to engine

• Leaks at lines and components of fuel supply system can sometimes be located using a non-flammable, environmentally sound leak detection spray. For this, initiate leak diagnostic several times in sequence to build pressure in the system. Leaks can be detected via bubbles.

- Visually check components of fuel supply system and EVAP system.

Fuel tank

EVAP canister

Leak detection pump (LDP) (V144)

Evaporative Emission (EVAP) Canister Purge Regulator Valve (N80)

• Because of shape or function of these components it is not always possible to find leaks by applying spray. It may be necessary to clamp off the relevant component using hose clamps (3094) and initiate leak detection diagnostic. If leak is no longer detected, the component that was clamped off is faulty. If clamp is placed directly on the diagnostic pump and a leak is still detected, then the diagnostic pump itself is leaking.