Sensors - Knock sensor

Knock Sensor
The knock sensor is sense the knock from the engine, create its own voltage and sent it to ECU.

Connect the knock sensor up to an oscilloscope, tap the end of the sensor and observe the waveform:

Explain why we are reading a voltage from the sensor when we are not supplying a voltage to it:

The knock sensor uses crystals or polycrystalline ceramic piezoelectric effect. When the engine cylinder block vibration, the piezoelectric elements inside the sensor press together and create voltage.

Sensor - IAT

IAT
  IAT means Intake Air Temperature sensor, it measures the air temperature and sent signal voltage to ECU.

Measure the resistance between the terminals.

Water Temperature ( Degree )	Resistance ( KR )
25	1.97
30	1.71
35	1.40
40	1.19
45	0.98
52	0.74
55	0.69
60	0.58
65	0.50
70	0.43

The graph:

The specification:

The sensor match the specifications. The temperature increase, resistance decrease. So the CTS is the NTC-Negative Temperature Coefficient thermistor.

The IAT sensor and ECT sensor is very similar and the circuit nearly the same. They are both using NTC thermistor function to change the available voltage output,  but one for the engine coolant and one for the air.

Sensor - Thermo Fan Switch

Thermo Fan Switch

  Thermo Fan Switch closes the cooling fan circuit when the engine coolant reach the temperature which it been designed.

Measure the resistance between the terminals.

Water Temperature ( Degree )	Resistance ( R )
21	2.7
25	4.8
30	6.1
35	5.1
40	4.4
45	3.2
50	2.6
55	1.3
60	0.8
65	0.7
80	0.7

The graph:

The TFW is faulty one. Because it is a switch, the resistance should be OL when it is opened, very low and constant resistance when it is closed.

The internal operation shows below:

The switch has 2 terminals, one ground and one voltage in. The voltage in terminal inside the switch constructed by 2 different types of  metal. When the temperature  raise up, the metal expand, one kind of metal expand more than the other one, so the terminal inside the switch bend to the ground terminal. When the temperature is high enough, the voltage in terminal contact to close the circuit to switch on the cooling fan. Also the the temperature goes down, the voltage in terminal bend backward and disconnect to ground terminal and turn off the fan.

Sensor - MAP, MAF

Map Sensor
  Map sensor means Manifold Absolute Pressure sensor. It can measure the air pressure in the manifold and sent the signal to the ECU.

Test the Map sensor

  Wire up a map sensor with a 5V feed and earth. Measure the return voltate from the third wire.

Vacuum Pressure = 0

Vacuum Pressure = 10cm Hg

Vacuum Pressure = 20cm Hg

Vacuum Pressure = 30cm Hg

Vacuum Pressure = 40cm Hg

Vacuum Pressure = 50cm Hg

Vacuum(cm HG)	0	10	20	30	40	50
Voltage(V)	3.68	3.28	2.88	2.48	2.09	1.70

The graph:

The manufacture specifications:

  The map sensor match the specification, when the vacuum increase, the voltage output decrease.

The map sensor can read both vacuum and pressure. When the vacuum increase, the voltage output decrease, and when the pressure increase, the voltage output increase.

Explain the internal operation of the sensor and why the output voltage changes.

  Here is the internal of the sensor:

  

 When the pressure or vacuum changes, the shape of the silicon chip flexes, and the resistance of the silicon chip changes. There is constant 5V supply on chip and the changing of resistance of chip, when the resistance of the chip (R1) changes, the available voltage after R3 and R1 changes, compared by the opamps and the voltage output to ECU changes.

MAF Sensor

  MAF sensor means Mass Air Flow sensor. It measure the mass of air flow through the manifold and sent signal to ECU.

The circuit of MAF sensor show below:

  When the air flow through the the MAP sensor, it cools down the thermistor and lows down the resistance of it. So the available voltage after thermistor increased. This voltage goes to the non inverting terminal of the opamps and compare the available voltage after the hot wire and turn on the power transistor to let current through. The current flow through the thermistor and heat it up back to base temperature and also flow through the hot wire to increase the available voltage after it, that is the voltage output signal to the ECU.

  

The Specification of the MAF sensor:

When the airflow increased, the output voltage increased.

Sensor - Vane AFM

The Vane AFM means Vane Air Flow Meter show as below

Test vane angle and voltage out

When vane angle is 0 degree

When vane angle is 30 degree

When vane angle is 45 degree

When vane angle is 75 degree When vane angle is 90 degree

Vane Angle and Voltage Out

Vane Angle	Voltage Out
0	3.81V
30	2.41V
45	1.37V
75	0.8V
90	0.35V

The graph

The specification of the AFM

  My results are within the manufacture's specifications. When the measuring plate opening, the voltage output increase.

Explain internal operation and why your voltage changes.

The circuit of it show as below

When the opening angle of the measuring plate changes, the resistance of Vs-Vb changes. E2 is ground,so the available voltage of Vs as the voltage output signal changes. Opening angle increased, rssistance between Vs and E2 increase, so voltage output increased.