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.
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HOMESERVICE MANUALSAUDI199590 QUATTRO SPORT V6-2.8L (AAH)REPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSAIR FLOW METER/SENSORDESCRIPTION AND OPERATION
1995 Audi 90 Quattro Sport V6-2.8L (AAH)
Air Flow Meter/Sensor: Description and Operation
1995 Audi 90 Quattro Sport V6-2.8L (AAH)SECTION Description and Operation
PURPOSE
The mass air flow sensor provides the Engine Control Module (ECM) with continuous information regarding intake "air mass." The voltage signal from the mass air flow sensor is used as an engine load signal. This load information is a major input variable for all load and speed dependent calculations such as: ignition timing, fuel injection time, activation of the evaporative emission frequency valve and idle speed adaptation.
OPERATION
In operation, a "hot wire" is heated to a temperature of 180°C (356°F) above ambient temperature. This temperature is maintained regardless of outside air temperature. As air flows through the sensor, the current through the wire increases to maintain the 180°C (356°) temperature. The current is sensed by reading the voltage drop across the measuring resistor in the sensor. Changes in intake air temperature are corrected by the compensating resistor. To clean the heated wire of contamination, it is heated to 1000°C (1800°F) for approximately one second when the engine is switched off.
CONSTRUCTION
The hot wire is mounted in an inner sleeve for protection. Each end of the mass air flow sensor also has a protective screen attached to help prevent damage to the wire.
COMPONENTS
^ Heated Wire (Platinum)
^ Measuring Resistor
^ Compensating Resistor
^ Micro Processor
The mass air flow sensor provides the Engine Control Module (ECM) with continuous information regarding intake "air mass." The voltage signal from the mass air flow sensor is used as an engine load signal. This load information is a major input variable for all load and speed dependent calculations such as: ignition timing, fuel injection time, activation of the evaporative emission frequency valve and idle speed adaptation.
OPERATION
In operation, a "hot wire" is heated to a temperature of 180°C (356°F) above ambient temperature. This temperature is maintained regardless of outside air temperature. As air flows through the sensor, the current through the wire increases to maintain the 180°C (356°) temperature. The current is sensed by reading the voltage drop across the measuring resistor in the sensor. Changes in intake air temperature are corrected by the compensating resistor. To clean the heated wire of contamination, it is heated to 1000°C (1800°F) for approximately one second when the engine is switched off.
CONSTRUCTION
Mass Air Flow Sensor:
The hot wire is mounted in an inner sleeve for protection. Each end of the mass air flow sensor also has a protective screen attached to help prevent damage to the wire.
COMPONENTS
^ Heated Wire (Platinum)
^ Measuring Resistor
^ Compensating Resistor
^ Micro Processor
RENDER: 1.0x
NO RELATED
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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.