Manifold absolute pressure sensor (431), E39
| Manifold absolute pressure sensor (431), E39 |
| Location |
Manifold absolute pressure sensor (431), E39
| Main task |
Engine load or air mass/combustion calculated with the mass air flow sensor (686) value can, during rapid changes in load, differ from the actual air mass drawn into the cylinder the the intake stroke.
This is due to the inertia of the large volume of air found in the intake system. During load changes, the intake pressure is therefore used to correct the air mass/combustion used when calculating the basic fuel quantity.
The manifold absolute pressure sensor (431) is also used to correct purging PWM ratio. With high intake pressure, a greater PWM ratio is needed to maintain the same purge flow.
The value from the pressure sensor (431) is also used as a substitute value for the mass air flow sensor (686) if the diagnostic system has detected a fault in the mass air flow sensor.
| Type |
The manifold absolute pressure sensor (431) contains two metal plated ceramic discs mounted in close proximity. The disc located closest to the pressure connection is thinner and bends when subjected to pressure. By this means, capacitance between the metal plating of the discs is changed based on the pressure.
| Connection |
| 431 pin no. | Signal type | Description |
| 1 | Supply voltage, 5 V | Connected to ECM pin 44(B). |
| 2 | Ground | Connected to ECM pin 63(B). |
| 3 | Signal | Connected to ECM pin 43(B). |
A circuit integrated in the manifold absolute pressure sensor (431) converts the capacitance to an analogue output voltage. The pressure sensor is secured in the engine's intake manifold after the throttle.
Based on the pressure in the intake manifold, the pressure sensor (431) yields a proportional voltage to the ECM control module (590), E39, pin 43(B). At normal atmospheric pressure, 100 kPa, output voltage from the sensor is approx. 2.1 V.
The manifold absolute pressure sensor (431) is mounted close to the atmospheric pressure sensor (539). Both are connected to the ECM as shown in the wiring table above.
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