Air Temp Sensor / On car

Air Temperature Sensor

The air temerature sensor (ATS) is also know as thermistor air (THa) and intake air temperature(IAT) sensor.This sensor is located in the ait cleaner box or sumwhere in the intake system. The air temp sensor helps the ecu calculate air density. Hot air is less dense than cold air. The ecu uses this information to do calculations for air fuel ratio mixes.

The IAT works exactly like the engine coolant temperature sensor. It is also a negative temperate coefficinet.When temperature increases resistances decreases and when temperature decreases resistace increases.

To do the experiment we did it like how we checked the ECT. As the IAT was made of plastic we didnt wana melt it by heating it up with a heater gun. And we also wouldnt have been able to know the temperature we heated it with. So we put it in water and heted it  over the stove. Temperatures were checked with a thermometer.At 20 degrees celsius the resistance was 2.9k. As we heated it up the resistance droped down to 800 ohms at around 50 degrees Celsius. This was within manufactures specifications and we could tell that the IAT was in good fine as the resistance gradually decreased when the temperature increased.  

Temperature (degrees celsius)	Resistance(ohms)
16	2.9k
20	2.5k
25	2.1k
30	1.7k
35	1.4k
40	1.1k
45	1k
50	800

On Car Intake Air Temperature

I found the IAT on the intake air clean box. I back probed the input wire  of the IAT and connected my multimeter to read DC voltage. Red probe to the input and the black probe to bappery negative post. Then i turned the igniton on.

I got a reading of 3.4v which is  more than the ECT voltage.

This shows that this is colder than the ECT sensor.

The IAT receives a 5v reference to the IAT thermistor. This is a NTC type thermistor which mean as temperature increases resistance will decrease. There is an internal resistor inside the ecu. When the air is hot, resistance decreases at the IAT so the voltage drop at the internal resistor is higher therefore less voltage goes to the IAT Input.The signal that the ecu looks at is voltage after the internal resistor as shown in the above wiring diagram. So when theres hot air signal sees a low voltage. When the air gets cold, resistance is high at the IAT and more voltage is needed to go through the thermistor so the signal sees a high voltage.

The IAT works with the MAP sensor to calculate the amount of air entering the engine. Cold air is more dense the hot air. So when the IAT senses cold air the ecu will need to open the injector longer to get the air fuel mixture right. If there is hot air entering the engine and the signal at the IAT is telling the ecu that theres cold air,the injectors will squirt more fuel making the air fuel mixture rich which will make the engine suffer from poor fuel economy and bad emmisions. If theres cold air getting in but the IAT is telling the ecu that theres hot air the mixture will be lean therefore the car will loose power.

Things that can cause an incorrect IAT signal to the ECU:

 - poor grounding at the ECU (connection corroded)

 - poor ECU grounding

 - Theres not a good supply voltage from the ECU

 - Open Circuit on the earth side or power side in the circuit

 - Bad thermistor

Thermo Fan Switch

Thermo Fan Switch

The Termo fan switch is mounted on the radiator core.The thermo fan switch is very important as it the switch to turn the radiator fan on and off. The switch is closed when it is cold and when it reaches a certain temperature there is an open circuit to turn on the fan.

We connected a multimeter to check resistance and put it in a bowl of water with the stove heating the water.We got a reading of 0.3 ohms which showed us that the switch was closed. When the temperature increased to about 93 degrees the meter read OL, which showed us that the switch was now open.So the fan would go on at around  93 degrees  Celsius to cool the radiator. This is not a thermistor. The thermo fan switch is working fine and is according to the manufacturer's specifications.

Engine coolant Temperature Sensor / On car

Engine Coolant Temperature Sensor

This sensor is also know as CTS (coolant temperature sensor) and THw (thermistor water). This sensor measures the change in coolant temperature. This sensor is generally located on the thermostat housing. This is a NTC (negative temperature co-efficient). this means when the temperature is high resistance is low and when the temperature is low resistance is high. This sensor is very important for cold starts to warm up the engine. The ecu enriches the fuel mixture and etc.

To do our experiment we connected our ECT to a multimeter to read resistance. We dipped it to a bowl of water which was on the stove to heat it up. Also used a thermometer to check the temperature of the water. The resistance decreased as the water heated up.At 20 degrees Celsius we had a resistance of 2.2k ohms and it decreased down to 300 ohms at 80 degrees Celsius. The readings i got is within manufactures specifications.

Water Temperature (degrees Celsius)	Resistance(ohms)
20	2.2k
30	1.8k
40	1.2k
50	800
60	600
70	400
80	300

The ecu has and internal resistor which reads the voltage after the resistor as show on the wiring diagram on the ECT, when the engine is cold there is a high resistance at the thermistor therefore there is a higher voltage drop at the thermistor so more voltage will be needed at the thermistor. Voltage drop at the internal resistor at the ecu is low and a higher voltage at signal is achieved. when the engine warms up there is a low resistance therefore a low voltage drop at the thermistor and a higher voltage drop at the internal resistor in the ecu, so a less voltage goes to the thermistor. The signal voltage is low because more voltage gets used up at the internal ecu resistor.

On Car Engine Coolant Temperature Sensor)

We located the Ect sensor and back probed the supply wire. Connected the multimeter (on DC volts) red probe to the supply and black probe to ground. We turned the igniton on.

With a cold engine we got a reading og 1.835V. When we started the  started the engine, the voltage decreased to 0.802V when the engine was at normal operating temperature. SO i conclude as the engine arms up the voltage at signal decreases.

I have described how the ECt works on top of the page in the off car part with the wiring diagram.

The Ecu gets information from the ect to see if the engine is cold or warm. If the engine is cold the ecu will make the car rich to heat it up quicker. This is done by opening the injectors longer. When the car warms up the engine will look at the ECT and re adjust injection timing.

Things that could affect the Signal voltage at the ecu :

 - Incorrect Reference voltage getting to the Thermistor due to a high resistance on the supply side.

 - Resistance at ground or the ecu having a bad ground. If theres a high resistance on the ground , the signal will have a high voltage which will tell the ecu that the engine is cold all the time.

 - the thermistor not working

Ground Coolant Temperature Sensor

I back probed the ground wire on the ect and connect my multimeter(on DC volts) red probe to the ECT ground and black probe to the battery post. I started the engine.

I got a reading of 0.3mV telling me that the grounding was good. It is very important to check the ground to dignose problems with the ECT. If the ect has a resistance at ground, the signal voltage will be high telling the ecu that the engine is cold. The ecu will then open the injectors longer making the car rich. The engine will suffer from poor fuel economy and bad emmisions.

Things that can cause this are are:

 - loose  grounding connections caused from vibrations and thermal stress.

 - Electrical terminals corroded by coolant

 - Loose ecu ground.

 - Battery terminal corroded not making a good connection with the negative battery post.

The wiring diagram is on the upper part of the page.

Mass Air Flow meter ( vane type)

Vane/flap type Air Flow Meter

The vane type airflow meter is diffrent to the hot wire type. This type has a mechanical moving vane/flap which moves in when there is air pressure. The vane moves in proportional to air flow and a voltage is sent out to the ecu in proportion to the distance the vane has moved.when flap opens the arm moves across a variable resistor. As the arm moves up and down along the resistor, the output signal voltage is changed which is sent back to the ecu.

With flap closed.

Flap wide open.

To do my experiment i connected my pinouts to the wiring diagram as above.5v reference at vc, 12 supply at Vb and earth at e2. Tha was the air temp signal. With vane close i got 4.48 volts and when i open it i got 1.4 volts.

Vane angle in degrees	Voltage
0	4.8
15	3.9
30	3.1
45	2.7
60	2.2
75	1.8
90	1.4

I couldnt check manufactures specifications as i dint know any part number or make and model of the sensor. To my knowledge is working fine as when we open the vane the voltage gradually decreases and increases as you relese the flap slowly.there is no break in the resistor.

Mass Air Flow Sensor

Manifold Air Flow Sensor (Hot Wire)

The maf sensor is located on the air intake after the air filter before the intake manifold.The mass air flow sensor sensors the amount of air drawn into the engine and sends a voltage to the ecu. A voltage is applied to the maf sensor to heat up the hot wire to about 100 degrees Celsius. The wires resistance increases as the temperature increases which allows less current to flow through the wire. when air passes through the maf sensor, it cools down the hot wire therefore resistance goes down and current flow increases getting the hot wire hot to its maintaining temperature. The amount of current required to get the hot wire back to its temperature is then converted by a chip in the maf to send signal voltage back to the ecu.

The hot wire has a self cleaning process. when the car is shut down, the hot wire heats up to about 1000 degress celsius to clean any dirt or grime stuck in the hot wire. If the hot wire gets contaminated and starts giving wrong readings there is no other way of fixing it then just to replace the piece.

without blowing air through maf.

blowing air though maf.

When i did the experiment i connected my bosch map sensor with the pinouts from the above table. i had to use to power supplies. A 5v and a 12V.without blowing air into the map i got 1.07v and when i blew air into it it increased to 2.2v.manufactures specifications tells us that the maf should have 0.5v at signal without air blowing thought it and out maf gave us 1.07. I think our maf is near to specification as we did the experiment in the class and there is a little bit of air flow as to the specifications are made to be done when the maf is connected to the intake and there is hardly any air flow when the engine is off. So i would say this maf is working properly.

Manifold Absolute Pressure Sensor / On car

Manifold Absolute Pressure Sensor

The map sensor is usually mounted on the firewall with a hose connected to the intake manifold.The map sensor is a very important sensor that sensors engine load. The sensor measures vacuum. More pressure is less vacuum and more vacuum is less pressure. At idle the vacuum is high as there is less air pressure in the engine. At open throttle there is more pressure therefore there is less vacuum in the intake manifold.

When i was testing my map sensor, i wired up a 5v supply and earth. Hooked up a multimeter to see the voltage at signal.I Then hooked up a mity-vac to the vaccum port of the map sensor. With no vacuum i got 4.8 volts at signal and as i applied vacuum with the mity-vac the voltage started to decrease. At around 70 cm Hg of vacuum the voltage got to almost .8v.

Vacuum cmHg	Voltage out
0	4.8
10	4.09
20	3.39
30	2.56
40	2.01
50	1.3
60	0.96
70	0.8

By my results its shows me that my map sensor is in good working condition and it is within the manufactures specification. My map sensor was a off a Toyota and i checked it with the toyota service manual that is posted on blackboard.

The map sensor reads vacuum to send out a voltage to the ecu. Theres is more vacuum at idle therefore its sends a low voltage telling the ecu theres less air in the inta`ke manifold. At wide open throttle there is less vacuum therefore the map sends a high voltage to the ecu. Its telling the ecu there is more pressure/air in the intake therefore the ecu adjusts injection timing and etc to give the engine optimum perfomance. 

On Car MAP Sensor

My engine had a map sensor. I back probed the signal wire of the map and connected my multimeter set to read DC volts. red probe to the signal and black probe ground. I turned the igniton on. I got a reading of 1.818V.

When i started the engine voltage dropped down to 0.541V.

When i revved the engine but just a short burst, the reading increased to 1.818v again.

When the ignition is turned the map reads the outside air pressure so we get 1.8v. As we start the engine at idle there is vacuum form the engine sucking in air so the voltage drops to 0.5v. When we are accelerating there is more air entering the intake, therefore more pressure and less vacuum so the voltage increases to 1.8 again. This voltage then tells the ecu that there is more air entering the intake so then the ecu increases the fuel into the air fuel mixture. This shows us that the readings we got was correct.

Problems that would send incorrect signal to the ecu from the MAP:

 - Vacuum leak in the intake

 - Leak on the map vacuum hose

 - The diaphram inside the map not holding vaccum.

 - poor grounding of the map ( high resistance on the ground)

 - Ecu grounding loose creating high resistance

 - corrosion on connectors

      

throttle position switch

Throttle Position Switch

 

This is the switch type tps sensor.This type only detects position at idle or at wide open throttle. This type uses contacts which work as switches. Switches are open or closes as the throttle position changes.

We did a resistance check with the tps switch to check if its working properly.We connected a multimeter on ohms to the idle pin and the ground pin and got a resistance o 0.3 ohms which told us that theres low resistance and good connectivity when the throttle was closed. As we opend the throttle a little bit to about 4 degrees the multimeter read OL. This meant that the switch was open now.

Now we connected the multimeter to the psw pin (wide open throttle. When the throttle was closed them meter read OL whcih meant the contacts were open. We started opening the throttle and to about 70 degrees of opening it read 0.4 ohms. This meant the switch was closed now and made connectivity. And the ohms ready told us that there is not a high resistance and connections are good.