PRE-RELEASE
Mass air flow sensor unit (686) EDC16
| Mass air flow sensor unit (686) EDC16 |
| Location |
Mass air flow sensor (686)
| Main task |
Measures air flow to the engine and the air flow temperature.
| Type |
Air temperature is measured with an NTC resistor.
Technical data
| Connection, mass air flow sensor 205 |
It is a common power supply via pins 1 and 2.
| Pin No. | Signal type | Description |
| 1 | Power supply | Connected to fuse 4 in UEC. |
| 2 | Ground | Connected to ECM pin 44(A). |
| 4 | Varying frequency | Connected to ECM pin 42(A). |
| Connection, temperature sensor 772 |
It is a common power supply via pins 1 and 2.
| Pin No. | Signal type | Description |
| 1 | Power supply | Connected to fuse 4 in UEC. |
| 2 | Ground | Connected to ECM pin 44(A). |
| 3 | PWM | Connected to ECM pin 37(A). |
| Function, mass air flow sensor 205 |
A measuring unit is located centrally in the air duct. A small portion of the intake air passes via a duct to a silicone diaphragm, which measures flow rate and direction.
A resistor network with temperature sensitive resistors and a resistor for heating are etched onto the diaphragm. The heating resistor is located in the centre together with a temperature sensor that controls the heating. The measuring resistors are located symmetrically on each side of the heating zone. If no air is passing the diaphragm, the heat will decrease linearly from the centre and out towards the edges and all the measuring resistors will measure the same temperature. When air passes the diaphragm, the edge and the measuring resistors closest to the incoming air will cool down while the resistors on the opposite side of the heating zone all but maintain their temperature as the air is heated when it passes the heating zone. The difference in resistance is compared with the reading from the temperature sensor in the measuring zone in a measuring amplifier and signal processor. In this way, the mass air flow sensor is able to determine the amplitude and direction of the air flow.
The output is a frequency as a function of the amplitude of the air flow. As the frequency is not crystal-controlled, the frequency of the temperature sensor can be used as a guideline value for how large the deviation is from the nominal frequency for a certain air flow.
| Function, temperature sensor 772 |
The temperature is measured by an NTC resistor whose value is converted to a PWM signal. The frequency is not crystal-controlled and its deviation from the nominal frequency can be used to compensate differences in frequency in the air flow value.
