I decided it might be nice for some people on here to learn how Sensors work and how to test them. I am attending Wyotech and by NO means do i know everything about ever sensor, but I will share what I know. People do make mistakes so feel free to correct me if im wrong.

I also will tell you how to test each sensor using a Digital Multi Meter or DMM. Never NEVER poke a hole into a wire to test it. always back probe the connector using t pins to test a wire.

Before you can understand how Sensors work you should have basic knowledge of electricity and how the PCM/ECU functions.

The PCM or Powertrain Control Module has 4 basic functions.InputProcessingstorageoutputs.

PCM receives a simple high/low, yes/no, on/off Voltage signal from the sensors and Most of the time is converted from an analog square wave signal into a digital signal. It is then processed into output voltage or a command. The PCM converts signals into Binary Code and is then read using the manufacturers software to do a command, usually turn something on or off.

Inputs to the pcm IncludeThrottle Position Sensor or TPSEngine Coolant Temperature or ECTKnock sensor or Detonation SensorEngine Speed sensor or Crank Position Sensor or CKPCamshaft Postion sensor or CMPVehicle Speed Sensor or VSManifold Absolute Pressure or MapMass Air Flow Sensor or MAFOxygen Sensor or O2

Outputs includeFuel InjectorsIgn timingIdle Air Control Valve or IACTransmission shifting in autos of courseEvaporative Emission Control solenoids

TPSWhat it is-The TPS is a Position Governed Variable resistor or potentiometer that modifies the voltage received from the PCM back to it.

What it does-Measures how fast and how far the Throttle Plates move.

How it works-The TPS is connected to the throttle plates. There is a needle inside the sensor that is contacting a variable resistor. As you accelrate or decelerate and the throttle plates move, the needle moves with it. The 5v's is applied to the needle that runs through the Variable Resistor and is then send back to the PCM.

How to test it- Turn Key on Engine off or koeoset your DMM to DC Volts.Most tps have 3 wires5volt ref Ground Signal back to the pcm

1. check your 5v ref to make sure your getting 5 volts2. check actual voltage at your signal back wire, at wide open throttle it should read close to 4.5v. Throttle plates closed should read close to .5v 3.Over time when the TPS is at a certain point where the needle contacts the Resistor for long periods of time, it will actually burn the contact point. The correct way to check this is using an oscilloscope. If your lucky you might be able to pick it up with a DMM. Your voltage reading should never hit below .5v or above 4.5v Fluxuate the throttle and watch your reading, if it drops off any time while your opening the plates the sensor is bad. if your reading is below 4.5v at wide open throttle and your receiving your 5vref, the sensor is bad.

ECT and IATWhat it is-Negative Temperature Coefficient Thermistor.Negative Temperature Coefficient-Resistance decreases as temperature increases. Thermistor-Resistance changes with temp.ECT and IAT work the same way and are both NTC.

What it does-Measures the temp of coolant and sends the reading back to the pcm, the pcm adjusts fuel and ign timing based on coolant temp.

How it works-has a sensor inside one or your coolant tubes usually close to the intake manifold. As temperature increases resistance in the sensor decreases and sends a voltage reading back to the PCM

How to test it- set your DMM to OHMS and check resistance of the sensor it self, will be a very high reading with engine off or cold, very low reading when engine is at operating temperature.

Knock SensorWhat it is-Piezo Electric sensor- pressure sensor.

What it does-senses engine vibration to detect detonation. actually produces Hash. which is a very abrubt change in wave length.When sensor voltage reaches predetermined level, PCM retards timing to protect from detonation.

How to test it- Knock sensors are almost always one or two wires. Set your DMM to DC volts. Connect it to your Knock sensor signal wire back to the pcm and take a screw driver and tap fairly hard on the Engine Block near the sensor. If you get a voltage reading the sensor is most likely in good condition. If you get no reading at all, it is bad.

CKP and CMP Both work the same way.What they are-2 types Variable Reluctance and Hall Switch type sensors.VR is basically an analog voltage genearator sensor.Hall Switch is digital signal generator.

What they do-CKP measures the exact position and speed of the crankshaft, CMP identifys the cylinders firing order by sensing the camshafts exact position and speed.

How they work-They work of magnetic induction.3 things needed for induction areMagnetic field- a permanent magnet attached to the cam/crankshaftConductor-Coil wire inside the sensor itselfMovement-The actual roatation of the crank/camshaft.The coil picks up the permanent magnet and senses how fast it is spinning and sends a voltage signal back to the PCM.

How to test them-set your DMM to DC volts.check actual voltage at the signal back wire. as engine RPM goes up so should voltage.

MAF and MAPWhat it is- 2 types speed density system which uses a MAP sensor.MAF type. im not going to go into the MAP sensor type because It is ridicuolsly confusing and frankly, i dont want to get into it right now.

There are 3 different types of MAF, Thermistor type sensors.Hot wire or Hot film, which RBs use.Karman Vortex and vane type which only Toyota used.

What it does-Measures mass and volume of air entering an engineMass=volume x Density

How it Works-A hot wire or a resistive heat element is placed directly into the air flowing into the engine. The pcm applys current to the wire and maintains a temperature of 100 degrees C regardless of ambient air temperature. as intake air volume increases, the hot wire trys to cool which requires more current from the PCM to stay at a constant temp.As intake air volume decreases the sensor trys to warm up so the PCM lowers the amount of current required to keep at 100 degrees C.

How to test it-Set DMM to DC volts, connect DMM to check actual voltage to the signal wire going to the pcm. as engine RPM increases the voltage going to the MAF should increase as well. Same goes if you decrease Engine RPM. Sould be around 4.5V at WOT

O2What it is-Piezoresistive sensormost newer vehicles have and upstream O2, before the catand a downstream O2, after the cat

What it does-measures oxygen content in exhaust

How it works-most O2 sensors are zirconia type. There is a small thymble of Zirconium Dioxide, an electrically conductive material that is possible of creating voltage in the presence of oxygen.

An O2 sensor does nothing in open loop operation, it is only used when in closed loop operation.to be in closed loop the O2 sensor has to be a minimum temp of 600 degrees F.Engine must be in a light load or cruising conditionPCM timer must have run out.It generates DC voltage in an analog wave form signal back to the pcm. Voltage is always between .1v and .9vAbove .5v is a rich condition low oxygen contentbelow .5v is a lean condition high oxygen content

When in closed loop operation the pcm uses the data from the O2 to adjust the PWM of the injectors to send more or less fuel.

how to test it- set DMM to MV and check actual voltage at the signal wire back to the PCM. start engine and allow engine to go into closed loop operation. voltage should be constantly changing as fuel is being added or subtracted from mixture.

outputsFuel Injectors function using Pulse Width Modulation-Turns a device on/off a fixed number of times. PCm can adjust PWM any rate between 0-100%Injectors are always measured in on time.

IACWhat it is- a stepper motor. turns in certain steps to create a full spin.

What it does- allows air to bypass the throttle plates so engine doesnt stall. at idle the throttle plates are closed not allowing air flow into the engine, so it would stall. also when your on the throttle, if you immideatly let off the throttle, the plates would close causing your engine to stall.

How it Works- A stepper motor works with magnetic induction. usually having 2,4 or 6 sets of windings. when the pcm tells it to open it opens in fixed steps. usually 120steps is fully open. PCM sends voltage to energize windings and is fully open when the windings are fully energized.

I hope this was helpful to someone, let me know if anyone has any questions, i will try my best to answer them.Also please someone correct me if im wrong or left anything out. I also have a surplus of information on this. this is about 1/4 of what i have on all the inputs and outputs. if anyone would like more information let me know.thanks

tyte! was that your homework assignment you just posted? keep up the good work!

slowrb20 wrote:
IACWhat it is- a stepper motor. turns in certain steps to create a full spin.

What it does- allows air to bypass the throttle plates so engine doesnt stall. at idle the throttle plates are closed not allowing air flow into the engine, so it would stall. also when your on the throttle, if you immideatly let off the throttle, the plates would close causing your engine to stall.

How it Works- A stepper motor works with magnetic induction. usually having 2,4 or 6 sets of windings. when the pcm tells it to open it opens in fixed steps. usually 120steps is fully open. PCM sends voltage to energize windings and is fully open when the windings are fully energized.

I hope this was helpful to someone, let me know if anyone has any questions, i will try my best to answer them.Also please someone correct me if im wrong or left anything out. I also have a surplus of information on this. this is about 1/4 of what i have on all the inputs and outputs. if anyone would like more information let me know.thanks

The nissan iac is not a stepper motor and we don't have hall effect cps.

how does the nissan iac work? and i knew we didnt have hall effect. i just posted both. and this was our horework and i have a test on it today. wish me luck haha

It's a duty cycle based valve, the ecu sends a pwm signal to it, the more duty % the more air will enter.

so then it would be a solenoid type iacv. i didnt know that.. thank you

I put A+ for the homework!!!

sorry to bring back from dead but... RB's use magnetic then? 3 or more wires ment hall effect i thought or the optic light/laser sensor?

Also just to add backprobing can do damage to the "waterproof connectors. If you have to poke just rub a little dielectric on it. Im also in a tech program and just had my test yesterday.

are you asking about the crank sensor?

mods make the corrections and make as a sticky! 4 noobs!

...christ to organize that into something coherent and easily searchable will be a task haha

regardless, great info for nubs.

lexrob wrote:sorry to bring back from dead but... RB's use magnetic then? 3 or more wires ment hall effect i thought or the optic light/laser sensor?

Also just to add backprobing can do damage to the "waterproof connectors. If you have to poke just rub a little dielectric on it. Im also in a tech program and just had my test yesterday.

Lol, when my CAS failed I was in phoenix attending UTI. Just so happened to be in our fuel and ignition course.. I took it off and we took the thing apart in class. Its an optical sensor and pretty damn cool inside if anyone gets bored and wants to take a look.

DriftingisLame wrote:
Lol, when my CAS failed I was in phoenix attending UTI. Just so happened to be in our fuel and ignition course.. I took it off and we took the thing apart in class. Its an optical sensor and pretty damn cool inside if anyone gets bored and wants to take a look.

I did something similar. I started cleaning up the oxidation on my CAS and opted to just open it up to polish housing. Pretty neat device. After looking at the 360 slits in the trigger wheel, I thought to myself "Now I hope I didn't just eff-up my CAS."

hey eric, an o2 sensor isn't piezoresistive, thats more map sensor territory (which can also be piezoelectric)

o2 sensors are chemical voltage generators. they sense a difference in oxygen molecules outside the exhaust compared to inside the exhaust which allows the oxygen sensor to create small amounts of voltage. damned wyotech drilled into my head lol