Have a Car Question? Ask a Mechanic Online.
Air Flow Meter/Sensor: Description and Operation
Mass Air Flow Sensor
The mass air flow sensor contains two PTC resistors RH) connected in parallel and situated in the airstream. They are electrically heated to 220CC above the air temperature.
Air temperature is measured with a special PTC resistor (RS).
As the air flow increases, a higher voltage is required to maintain the temperature difference at a constant value. The voltage required is converted to ground pulses, the frequency of which increases with the air mass flow.
The mass air flow sensor is grounded to grounding point G7 and is supplied with power from the main relay. Note that the Control module has a pull-up to 5 V' on input pin 65 and the mass airflow sensor pulses to ground.
When the ignition switch is turned to the "ON" position, the main relay operates and B+ is supplied to pin 3 on the mass air flow sensor. A current passes RT and the low-ohmic Thermal resistors RH via R1 to ground. As the RH resistors are cold. Their resistance is low. The amplifier then sends a strong base current to transistor T1. whereby RH rapidly heat up. As RH heat up. The resistance increases and a state of equilibrium is achieved. If RH are cooled by the airstream. Their temperature will be reset immediately by an increase in current through transistor T1. The voltage required to keep the resistance of RH constant is fed to a frequency converter, which in turn Controls transistor T2. T2 grounds the Control module input with a frequency corresponding with the air mass flow. The ground pulses have a duration of 40 ms.
The temperature sensor resistor RS is included in a circuit together with R2. The objective of which is to correct amplifier A so that the temperature of RH is always 220 CC above the air which is to correct amplifier A so that the temperature of RH is always 220 CC above the air temperature.
The Control module coverts the frequency to grams per second and Then, assisted by the value from the crankshaft position sensor, to milligrams air per combustion. The unit is written mg/c (milligrams per combustion) and constitutes the principal value for the Fuel injection. Normally. 1 mg Fuel is consumed at 14.7 mg/c. The value is also a good indication of the engine torque or load.
Three different diagnostic trouble codes can be generated if the mass airflow sensor develops a fault:
- If the mass air flow sensor does not send a frequency at all to the Control module, diagnostic trouble code P0100 will be generated. This can be due to a break in one of
- If the frequency is too low, diagnostic trouble code P0102 will be generated. This can be due to a major leak between the mass air flow- sensor and the throttle body or and internal fault in the mass air flow sensor.
- If the frequency is too high, diagnostic trouble code P0103 will be generated. This can be due to and internal fault in the mass air flow sensor.
System reaction to a fault
Manifold Absolute Pressure Sensor
Inside the pressure sensor there are two metal-plated ceramic discs mounted close together. The disc situated closest to the pressure connection is thinner and bends when exposed to pressure. This changes the capacitance between the metal-plated discs depending on the pressure. Integrated in the sensor is a circuit that converts capacitance to analogue voltage. The pressure sensor is screwed to the intake Manifold on the engine after the throttle and is powered with 5 V from Control module pin 69 and grounded from Control module pin 22. Depending on the pressure in the intake Manifold, the pressure sensor delivers a voltage to Control module pin 11.During rapid load changes, the engine load or calculated air mass combustion based on the mass air flow sensor value can differ from the actual air mass being taken into the cylinder during the induction stroke. This is due to the inertia of the large volume of air present in the intake system. The intake pressure is therefore used during load changes to correct the air mass combustion used in the basic calculation of the Fuel quantity.
The pressure is also used to correct the purge PWM ratio. A greater PWM ratio is required at high intake pressures to obtain the same purge flow. At normal atmospheric pressure. 100 kPa. the pressure from the sensor is approx. 2.1 V. Image
- If the sensor voltage is too low. Diagnostic trouble code P0107 will be generated.
- If the sensor voltage is too high, diagnostic trouble code P0108 will be generated.
- If the pressure value is implausible, diagnostic trouble code P0106 will be generated.
- Correction of air mass combustion for Fuel calculation is blocked.
- Purge blocked.
MORE TO COME.....
what additional info do you require
Intake Air Temperature Sensor
The pressure sensor is combined with a temperature sensor and measures the current absolute pressure and temperature in the Charge air pipe.
The NTC-type temperature sensor is located in the intake Manifold. The Control module measures the air temperature in the intake Manifold by supplying the sensor with 5 V through an integrated 2.74 kohm resistor from pin 15. The sensor is grounded from pin 70. The voltage across the resistor in the Control module is proportional to the intake air temperature.
The temperature is used to:
- Determine the density of the Charge air together with Charge air pressure. The Charge air density is used by the air mass Control to correct the throttle angle.
- Correct the PWM ratio of the Charge air Control valve. A higher PWN ratio is required at high temperatures to obtain the same air mass combustion.
- Correct the ignition timing. A more advanced ignition is required at low temperatures.
- Block certain diagnoses:
- Blocks certain diagnoses at temperatures lower than -7CC.
- Reactivates certain diagnoses at temperatures higher than +5CC.
- If the sensor voltage is too low. Diagnostic trouble code P0112 will be generated.
- If the sensor voltage is too high, diagnostic trouble code P0113 will be generated.
- The Control module sets 40CC as a substitute value.
- Density compensation of the throttle angle is blocked.
i dont know havent been back to the shop was waiting for your reply to give them the specs
thank you will let you know if not too late but i believe they closed at 5 est