4848 Blog 1 off-car sensor testing

In this blog I am going to introduce 4 sensors which I tested in 4848 Vehicle Electronic Controls off-car practice.

*** TPS - Throttle Position Sensor
*** MAP - Manifold Absolute Pressure Sensor
*** ECT - Engine Coolant Temperature Sensor
*** IAT - Intake Air Temperature Sensor


*** TPS - Throttle Position Sensor


Background:


A Throttle Position Sensor is a ECU controlled device that normally located on the butterfly spindle of a car which monitor the position of the throttle plate.
Why is it important ?
The ECU needs to know the position of the throttle butterfly so it knows how much fuel to inject to make the best air-fuel ratio.The TPS works with MAP sensor in non-turbocharged vehicle.
Modern engines are equipped with a TPS that has a magnet and Hall Effect Sensor in it which we describe it as Non-Contact Type, but the older ones that we are going to test is the potentiometer type which the two metal parts inside contact each other when throttle butterfly turns from closed to WOT(wide open throttle), while it rotates the resistance changes and alters the output signal to ECU.

This a photo of TPS mounted on the throttle body 

Symptoms of a bad TPS:

*** Car bucks and jerks
*** Engine idle surges
*** Engine sudden stalls
*** Hesitation when car accelerates
*** etc......

It may cause serious problem and even accident with a bad or faulty TPS.



Theory:


How it works?
The potentiometric type Throttle Position Sensor is actually a potentiometer which has a slide contact rotates when the throttle butterfly rotates,during the rotation the resistors' resistances inside of it changes which varies the output voltage so ECU knows what is the position of the throttle plate.
Most throttle position sensors have at least 3 wires, they are 5V input from ECU, an earth and an output signal back to ECU.

This a diagram shows a basic TPS wiring circuit

As we can see, a resistor inside the ECU will decrease the battery voltage to a 5V reference voltage which supplies to the sensor, the current will flow through another resistor inside the sensor and back to the ground terminal in the ECU, and the wire in the middle is the signal voltage.
If the TPS is working normal,the output votalge should increases when throttle opens wider due to less resistances.

Experiment:


Test this TPS:
We will only need a multimeter to test this TPS


Get ready:

1. Connect a 5V from power supply to the input terminal
2. Set the multimeter to voltage test and connect the red probe to the signal terminal
3. Ground the earth wire with the black probe of the multimeter to the ground of power supply

Then:

1. Turn on the power supply,we should now get a reading with throttle butterfly shuts
2. Start turning the throttle butterfly and check the voltage output reading when it is at different angles

This is the results and graph shown below:

The results above was completely wrong so I did another testing on the same sensor which had result shown below

Reflection:


After the second testing I corrected my knowledge a big time, I used to think the voltage should decreases when throttle plate opens wider but that was incorrect, the voltage should definitely increases when throttle opens wider.
The second result shows the TPS was in a good working order as the output voltage varies between 0-5V while throttle plate opens and closes.
A TPS works together with a MAF(Mass Air Flow) sensor or MAP(Manifold Absolute Pressure) sensor to tell ECU the information about incoming air, however if a TPS is faulty, the engine will run bad at slow speed or very rough idling.

References:

auto101.com

wikipedia

Unitec Moodle

Vijay Naidu

*** MAP - Manifold Absolute Pressure Sensor





Background:


A MAP sensor is used to get instantaneous manifold pressure information for ECU in a fuel-injection engine.MAP sensors are called Manifold Absolute Pressure sensors rather than Intake Vacuum Sensors because they measure the PRESSURE inside the intake manifold.
When the engine is not running, the pressure inside is pretty much the same as the pressure outside the engine, but as soon as the engine started up, the vacuum is created as the pistons are doing pumping actions and the throttle plate stops more air coming, but the vacuum will drop while throttle plate opens and will reach to the minimum once the throttle is wide opened.
A MAP sensor can be mounted on the manifold or somewhere near the manifold with a vacuum hose connected.
Why is it important?
The MAP sensor is a key sensor because it directly senses engine load.The ECU needs to know how much air going in to manifold so it can calculate air density and determine the engine's air mass flow rate,which also calculate fuel requirement and send out signal to injectors. 

A photo shows you how a MAP sensor look like

Symptoms of a bad TPS

*** Engine idle surges
*** Fouled spark plugs
*** Loss of power and bad fuel costs  
*** etc......

If a MAP sensor is faulty,it will effect engine's working condition directly and cause it running bad,a MAP sensor is always working with a TPS,they both send out signal to ECU to let it know how much air is flowing into cylinders so ECU can calculate and send out information to injectors




Theory:


How it works?
A MAP sensor sends out different voltage singal to ECU depends on how much pressure the manifold is getting by different resistances which is the same to a TPS.However the differences are there is a silicon chip which changes its resistance when pressure alters that mounted inside a reference chamber in a MAP sensor,one side of the chip is at a calibrated pressure which is a reference pressure and the other side of the chip is the pressure that actually to be measured.
A good MAP sensor will read between 1V-4.5V depends on the engine load, the vacuum will be the highest when the car is at idle so the output voltage will read very low because there's a lot resistance and voltage will increase with throttle opens wider.

A simple diagram can show you the wiring circuit

A resistor in the ECU will drop the battery voltage to a 5V reference voltage which supplies to the sensor, the current will flow through another resistor inside the sensor and back to the ground terminal in the ECU, and the output signal wire is in the middle and voltage will change with pressure changes. The way how a MAP sensor works is very similar to a TPS sensor





Experiment:


Test MAP sensor:
We will need a multimeter and a vacuum tester to test this MAP sensor

Get ready:

1. Connect a 5V from power supply to the input terminal
2. Set the multimeter to voltage test and connect the red probe to the signal terminal
3. Ground the earth wire with the black probe of the multimeter to the ground of power supply

Then:

1. Turn on the voltage supply,we should now get a reading.
2. Connect the hand vacuum tester to the vacuum port of the sensor, start pumping air in it and check the output voltage on the meter at different mercury

This is the results shown in a graph below:

This result shown above was incorrect and I did another test on the same sensor which has the result below:

 

Reflection:


As we can see it was a straight line on the graph of the first testing, it shouldn't be a perfect straight line as the pressure will not change evenly, the pressure will increase rapidly when the throttle opens closer to the maximum so the voltage will increase faster than before like the line on the second graph.


When there is more vacuum there will be less voltage


A MAP sensor works together with a TPS to tell ECU the information about incoming air, however the ECU depends on the MAP more than TPS when it is having huge engine load.

References:

auto101.com

wikipedia

Unitec Moodle

Vijay Naidu

*** ECT - Engine Coolant Temperature Sensor


Background:

A ECT sensor is actually a NTC(Negative Temperature Coefficient) thermistor, it is usually screwed into the coolant passage where coolant can pass the bottom part of the sensor with 2 wires coming out of it. It is necessary for the electrical fuel-injected vehicle as it is more efficient for ECU adjusting the best air/fuel ratio when the engine is cold.

Why is it important?
When the engine is cold,it needs more fuel injection and faster ignition timing,so this is what the ECT sensor does before it leaves this job to ECU itself.In some cars it also turns on the electrical fan when the coolant gets very hot, there is another sensor mounted somewhere near the ECT sensor with only 1 wire coming out of it is for providing readings for the coolant temperature gauge on the dash.

A photo shows you what a ETC sensor looks like:

Symptoms of a bad ECT sensor


*** Engine runs rich
*** Car emission increases
*** Engine shuts down
*** etc......

The ECT sensor is really important especially when engine is cold,a faulty ECT sensor will cause engine runs rich which not just bad fuel economy,it also produces more engine wear which it will reduce its liftime.



Theory:

How it works?

A ECT sensor usually comes with 2 wires which one of them is 5V input from ECU (also provides feedback signal back to ECU) and the other one is ground.Because it is actually a NTC thermistor inside so it can change its resistance depending on the coolant temperature which varies the output voltage so ECU knows how cold or hot the coolant is
If the sensor is working normal the resistance should be higher when the temperature is lower and resistance gets lower when temperature gets higher.

Here is a simple diagram of the wiring circuit for a ECT sensor:

Just like most of the sensors, there is a resistor inside the ECU which will drop the battery voltage to a 5V and supplies to the sensor, current will flow through another resistor in the sensor and back to the ground terminal in the ECU, the ECU will read the different signal from THW wire based on the temperature of the coolant.




Experiment:

Test this ECT sensor:

We will need a multimeter,a gas heater and a container of water to test this ECT sensor

Get ready:
1) Put the ECT sensor side in the water and have the heater ready to heat
2) Adjust the multimeter to ohms test and connect the probes to the 2 ternimals and we should get a ohms reading


Then:
1) Turn on the heater
2) Write down the resistance at certain degree of the water from start upto 90 degree

This is the results and graph shown below:

I rounded up the result in the above test which is not good, I should have the exact reading written so I did another test on the same sensor and here's the result below:

Reflection:


This is a ECT sensor I picked from the classroom randomly so unsure what engine that it came off, however different manufacturer will make the sensor have different resistance so the output voltage will not be the same, to check a ECT sensor on car we will need to find out the resistance or the output voltage range from the engine manual of the vehicle.


If the ECT sensor is faulty and makes wrong signal to the ECU, the ECU will run rich and cause bad fuel economy, and may fill the pistons with fuel and kill the spark plug so the engine will be hard to start.

References:

auto101.com

wikipedia

Unitec Moodle

Vijay Naidu

*** IAT - Intake Air Temperature Sensor




Background:


A IAT sensor is very similar to a ECT sensor which is a NTC thermistor,but it is usually screwed into the intake system after the air filter and before the throttle body with 2 wires coming out of it. It is working to help the ECT sensor to detect what is the temperature of the engine in the electrical fuel-injected vehicle, it is more efficient for ECU adjusting the best air/fuel ratio when the engine is cold.

Why is it important?
ECU needs to know correct engine temperature for the proper amount of fuel to be injected,this includes coolant temperature,intake air temperature and even exhaust temperature for best air-fuel ratio.A IAT sensor is less important than a ECT sensor but they are work for the same purpose in the same way


Symptoms of a bad IAT sensor

*** Starting time extents
*** Fuel consumption
*** etc......

A IAT sensor looks similar to a ECT sensor which is shown below:

Theory:




How it works?
A IAT sensor is exactly the same with a ECT sensor which usually comes with 2 wires which one of them is 5V input from ECU (also provides feedback signal back to ECU)  and the other one is ground.Because it is actually a NTC thermistor inside so it can change its resistance depending on the intake air temperature which varies the output voltage so ECU knows how cold or hot the air is.
If the sensor is working normal the resistance should be higher when the temperature is lower and resistance gets lower when temperature gets higher.

The diagram is shown below:

Experiment:


Test this IAT sensor is the same way to test a ECT sensor:

We will need a multimeter,a gas heater and a container of water to test this IAT sensor


Get ready:
1) Put the IAT sensor side in the water and have the heater ready to heat
2) Adjust the multimeter to ohms test and connect the probes to the 2 ternimals and we should get a ohms reading



Then:
1) Turn on the heater
2) Write down the resistance at certain degree of the water from start upto 70 degree



This is the results and graph shown below:

I made the same mistake as the test for ECT sensor about rounding up the result, the new result of second testing is shown below:

 

Reflection:

Very similar to the ECT sensor, his is a IAT sensor I picked from the classroom randomly so unsure what engine that it came off, however different manufacturer will make the sensor have different resistance so the output voltage will not be the same, to check a IAT sensor on car we will need to find out the resistance or the output voltage range from the engine manual of the vehicle.

References:

auto101.com

wikipedia

Unitec Moodle

Vijay Naidu