4848 Blog 2 Input Sensors and Actuators On-Vehicle Part 1

For 4848 blog 2 and 3, I am going to explain my testing and results of the input sensors and Actuators on- vehicle

In part 1, there are 3 sensors will be introduced and tested on cars which are:

Throttle Position Sensor

Engine Coolant Temperature Sensor

Crank Position Sensor

For testing these sensors,we will need a multimeter and some pins for back probing

Throttle Position Sensor:

Background:

The most common type of 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.
If the TPS is working normal,the output votalge should increase when throttle opens wider due to more resistances.

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.






Theory:

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.

There are 3 things which can identify whether the sensor is in good working order or not

*** Reference voltage

*** Sensor ground

*** Output voltage

The purpose of testing the reference voltage is a TPS needs a reference voltage supplied to work, if there isn't, the TPS won't be able to work therefore it can not read the resistance of the potentiometer inside and can not deliver the correct signal to ECU,the ECU will end up sending wrong signal to fuel injection system,it is very important to do so.
A bad or rusty earth/ground connection is actually acting as a resistor and will give extra resistance of the circuit which changes the output voltage and deliver wrong signal to the ECU.






Experiment: 

The vehicle I used to test this sensor is a 1997 Honda Civic 1.5L

First of all, I found the TPS just sitting under the air box mounted on the throttle body,then I back probed all 3 wires with 3 pins.


Here is a photo I took of this sensor

I set it to DC volt and hooked up the red lead of my multimeter with one of the 3 pins when the ignition is ON and engine is OFF, then I started checking wire by wire until I found out the brown wire read 5.07V which this wire is the reference voltage wire and it has a good reading according to the manufacturer's specifications 

In this case the TPS is having good reference voltage but if it isn't, it might be a problem with ECU,bad wiring loom or connection.

After finding and testing the input voltage terminal,now I use the same way to find and test the ground wire,a good ground will usually read less than 0.05V according to the workbook

The multimeter showed 0.02V when the black wire is hooked up with the red lead and yes this reading told me the ECU earth is good

At last, I needed to test the last wire which is the signal wire.

With the ignition is ON and engine is OFF,I hooked up the signal wire with the red lead of my multimeter and got the reading showing : 0.76V,then I opened the throttle to about the half open position and got the reading showing: 2.89V and 4.05V when the throttle was opened to the full open position.

Reflection:

According the manufacturer's specification,these reading that I got is showing that this TPS is in good working order.

A normal TPS should has a lower output voltage when the throttle butterfly is shut and output voltage increases with throttle butterfly opens wider

A faulty TPS can make the engine no or not enough power,stall or running roughly due to not enough fuel

Not a faulty TPS itself can cause problems,some other things such as faulty ECU,bad wiring/connection will also make a TPS not working properly even it is a good TPS.

References:

auto101.com

wikipedia

Unitec Moodle

Vijay Naidu

Engine Coolant Temperature Sensor

Background:

A ECT sensor usually comes with 2 wires which one of them is 5V input from ECU and the other one is ground and also the feedback to ECU.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.
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.

Theory:

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 to ECU.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. 

There are two things which can identify whether this sensor is in good working order or not

*** Sensor ground

*** Output voltage

A bad or rusty earth/ground connection is actually acting as a resistor and will give extra resistance of the circuit which changes the output voltage and deliver wrong signal to the ECU

Different ECT sensor will have a different resistance range according to how manufacturer designed it, but all the output voltage should vary between around 1V to 4.5V.

Experiment:

The vehicle I used to test this sensor is a 2008 Mitsubishi Cedia Wagon

First of all, I found the ECT sensor is just sitting on the thermostat housing,then I back probed the 2 wires with 2 pins.


Here is a photo of this sensor

Note: the ECT is the sensor connected with the pin and jumper lead which it is not visible on this photo.

I set it to DC volt and hooked up the red lead of my multimeter with one of the 2 pins when the ignition is ON and engine is OFF, then I started checking wire by wire until I found out the white wire read 4.97V which this wire is the voltage input from the ECU.

After finding and testing the input voltage terminal,now I use the same way to find and test the ground wire,a good ground will usually read less than 0.05V according to the workbook

The multimeter showed 0.017V when the black wire is hooked up with the red lead and yes this reading told me the ECU earth is good

At last, I needed to test the output voltage which is the same wire of the voltage input wire.
And also the engine must be cold at first then start up and let it to warm up to test the output voltage change.

With the ignition is ON and engine is OFF,I hooked up the signal wire with the red lead of my multimeter and got the reading showing : 3.49V and this told me that the engine was cold.Then I started up the engine and let it warm up for about two mins and recorded the voltage of the ECT at that time which was 2.14V.

Reflection:

A warmer engine will always have less output voltage reading due to less resistance than when it is cold,this theory testifies that the results above shows this ECT sensor is in good working order

A faulty ECT sensor will make symptoms such as engine runs rich,car emission increases or engine even shuts down

Not a faulty ECT itself can cause problems,some other things such as faulty ECU,bad wiring/connection will also make a ECT not working properly even it is a good ECT.

References:

auto101.com

wikipedia

Unitec Moodle

Vijay Naidu

Crank Position Sensor

Background:

A CPS sensor is used to monitor the position or rotation speed of the crankshaft,this information is used to control ignition timing and tell driver the engine revolution.

The CPS can be used in combination with a similar Camshaft Position Sensor to monitor the relationship between the pistons and cam valves in the engine, which is very important in variable valve timing engines


A CPS can be mounted on the crank pulley, flywheel or just on the crankshaft itself, it is one of the most important sensor in the modern engines, without its working, the engine may not start, stall when it is running or running in the very bad ignition timing


The most common types of CPS are either a Reluctor type or Hall Effect type.






Theory:




A reluctor  type is like a generator. It is a coil with wires wrapped around an iron core and usually have a magnet at one end. When a steel tooth passes the iron core it effects the magnetic field and creates a voltage at the end of the wire. The signal out of the sensor is like AC voltage. It will always make a analogue waveform.


For a hall effect type normally there are several pins placed on the crankshaft which also spaced an equal distance apart from each other.The magnet next to the crankshaft generates a constant magnetic filed when the crankshaft rotates,the rotation pins cause the field to vary.The sensor uses this magnetic change to determine the speed and the position of the crankshaft. It will always make a digital waveform.

There are couple of things can testify whether this sensor is in good working order or not

*** Reference voltage

*** Sensor ground

*** Output voltage

*** Sensor Hz

The purpose of testing the reference voltage is a CPS sensor needs a reference voltage supplied to work, if there isn't, the CPS sensor won't be able to work therefore it can not determine the speed and position of the crankshaft.


A bad or rusty earth/ground connection is actually acting as a resistor and will give extra resistance of the circuit which changes the output voltage and deliver wrong signal to the ECU

We also need to know the frequency of the sensor because we need to make sure it responses to every rotation of the crankshaft no matter how fast or slow it goes.

Experiment:


The vehicle I used to test this sensor is a 2008 Mitsubishi Cedia Wagon


First of all, I found the CPS sensor is sitting on the left side of the engine closer to the pulleys,then I back probed all 3 wires with 3 pins.


Here is a photo of this sensor

I turned on the multimeter to DC volts and hooked up the red lead of my multimeter with one of the 3 pins when the ignition is ON and engine is OFF, then I started checking wire by wire until I found out the yellow/red wire read 5.11V which this wire is the reference voltage wire and it has a good reading according to the manufacturer's specifications 

In this case the CPS sensor is having good reference voltage but if it isn't, it might be a problem with ECU,bad wiring loom or connection.

After finding and testing the input voltage terminal,I used the same way to find and test the ground wire,a good ground will usually read less than 0.05V according to the workbook

The multimeter showed 0.03V when the black wire is hooked up with the red lead and yes this reading told me the ECU earth is good

Then I needed to test the output voltage which is the white/brown wire, because the CPS generates AC volts so I set the multimeter to read AC volt and I hooked up this signal wire with the red lead of my multimeter and got the reading showing : 1.95V after I started up the engine and 2.93V when the engine RPM increased to 2500rpm.

The last thing I needed to check was the sensor Hz, use the same way as above but set the multimeter to read Hz and I got the reading showing 0.41Hz at idle and 1.36Hz when the engine RPM increased to 2500rpm.

Reflection:




I did not get a photo of the waveform from the testing, but I can remember the waveform was a clean square digital waveform which drops all the way to ground.


The waveform indicates this CPS is a Hall Effect Type and all these readings above shows this CPS is in good working order according to manufacturer's specifications.

A faulty CPS sensor will make engine fires in wrong ignition timing and wrong signal to tachometer on dash.

Not a faulty CPS itself can cause problems,some other things such as faulty ECU,bad wiring/connection will also make a CPS not working properly even it is a good CPS.

References:

auto101.com

wikipedia

Unitec Moodle

Vijay Naidu