Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Leak Diagnostic Unit
The function of the leak diagnostic unit is to pressurize the fuel tank system during leak diagnostics and to open the fuel tank system to the surrounding air during evaporative emissions control.
The leak diagnostic unit consists of a plastic housing with:
- electrical air pump
- a valve / solenoid which governs the air flow in the unit
- a heater element (PTC resistor) which warms up the pump.
The electrical pump, valve and heater element in the unit are supplied with voltage by the system relay. The pump, valve and heater element are grounded (control) in the engine control module (ECM).
During leak diagnostics the pump in the leak diagnostic unit starts. The valve in the unit is operated by the engine control module (ECM) by grounding the different circuits internally in the engine control module (ECM). Operation depends on whether the diagnostic phase is checking for leakage or checking the function of the diagnostic system. The engine control module (ECM) gauges the power consumption of the pump during pressurization. The power consumption corresponds to a certain pressure in the fuel tank system. See also: LEAK DIAGNOSTICS (CERTAIN MARKETS ONLY)
The engine control module (ECM) can diagnose the leak diagnostic unit.
The valve in the leak diagnostic unit can be activated and the power consumption of the pump can be read off.
The leak diagnostic unit is at the upper front edge of the fuel tank.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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