Input Sensors and Actuators On-Vehicles

Fuel injector. Supply voltage 14.59 volts. Negative trigger actuator. Supply voltage has to be checked as its important for injector to have power to operate. If voltage supply low at injector it may affect open time and duration of injector and will effect performance of the vehicle.

TPS sensor. There are two types of TPS sensors, one is a switch and another potentiometer or linear resistor type. Linear resistor has got 5 volts reference voltage (supply voltage) and a variable resistor track inside and varies output voltage depending on variable resistor. When throttle closed resistance is high and output voltage low, but when its fully open resistance is low and output voltage is high. With this sensor ECU always know at what state is a throttle and can determine how much fuel to add and use emission systems and actuators when vehicle at light cruise. When reference voltage incorrect because high resistance in supply wires (corroded or not plugged in properly) or broken wires because or damage or incorrect testing, this can cause ECU thing wrong and receive half open throttle signal when its wide open. This can effect on fuel economy, emissions and incorrect engine performance. Also ground wires can cause problems, good ground voltage drop reading is usually lower then 0.05 volts if they have a high resistance at ground because of loose connection or corroded wires the can create a high voltage drop at location of the problem and also effect output voltage to ECU from TPS esnsor. And finally ECU ground should be in good working order as it can effect our reference voltage to the sensors, not just TPS as most of the automotive sensors use 5 volts as a reference voltage. So its important when testing TPS to check first supply voltage or reference voltage and second good ground to the sensor. Also some TPS sensors have a fourth wire which can be an idle switch, this is when throttle closed and no air coming to the engine, so ECU know that it need to open idle control valve to keep engine running.
Other type is a switch, its only shows engine 3 modes, idle, light cruise and wide open throttle. Simple but still sensor. Not used on late model cars as less accurate.


ECT or engine coolant temperature sensor. This sensor tells ECU current operating temperature of the engine. It determine cold start injectors cycle and control richness of air fuel mixture at cold start, until engine hot enough end ECU goes into closed loop.
I used a multimeter to check voltage drop at ECT and recorded 2.47 volts which showing engine still warming up and reading on the temperature gauge was just below quarter. Then we started engine again and ran for couple more minutes. I check voltage again and it was 1.27 volts and temperature gauge showed around 2/3 of the scale. This indicates that sensor working well as with increasing of engine temperature voltage reading should go down and warmer engine should show low voltage then colder engine. This sensor is an Negative temperature coefficient (NTC), which means it will decrease its resistance the hotter it goes, and it could be over 20000 Kohms when temperature -10 degrease or around 200 ohms when its at 80 degrees.Also we have done ground wire check of ECT sensor and recorded 0.037 volts, which is good result as it must not exceed 0.05 volts at the ground wire (terminal). So with this controls engine when its cold, if it would work properly the car would go into closed loop or even can struggle to start in the morning. It could be old and ineffective or even just can have high resistance because of corroded or oily ground wires or even have a brake in the voltage supply wires. Also this sensor receives reference voltage of 5 volts from ECU and if ECU ground wire got corroded and have high resistance it will effect on reference voltage by lowering it and in this case it will be lowered to all our sensors which receive 5 volt reference voltage.

RPM sensor or Crank Position sensor (CKP).

Here is some readings of RPM sensor in AC volts, DC volts and Hertz.
We used magnetic pick up sensor and AC volts and Hertz showing better then DC volts that its working.
This type if RPM sensor is an AC generator, it produce AC voltage when rotating and the number tips on the shaft indicate on number cylinders in the engine. AC volt function of multimeter tells us how much voltage it generate for every tip passing the sensor magnetic pick up and a Hertz tells us how fast its rotating, as if speed of the shaft increased it increases frequency of rotation, so it start to rotate faster and get more revolutions per minute. Most of this sensor has got adjustable gap between tip and magnet, so if the gap is too big it wont generate signal or it could be weak and not enough to work properly, also they have a certain life and if not working, must be replace as non fixable item.


MAF or MAP sensor. We have tested a MAP sensor on a 4AFE Toyota corolla engine. First we recorded output with engine off and its 0 volts as its no reference voltage supply to the sensor. Then we just turned ignition on without starting the engine and it was 3.67 volts. Then engine was started and reading was 1.41 volts at idle and after we did fast but short acceleration and recorded 2.24 volts.
Inside MAP sensor is a silicon chip which changes resistance with different pressure inside intake system and this changes output voltage to ECU. When engine at idle its almost no pressure inside intake (vacuum) so its gives low voltage output, but when throttle open, engine starts to accelerate and pistons suck more air inside, they create certain pressure under different engine loads and change output signal of MAP. This sensor tell ECU how much load on the engine and how much goes in so it can choose how much fuel to inject. Also inside map sensor is a Winston bridge with one constant resistor and one variable resistor (silicon chip). It could be a lot of things which can interrupt this sensor, such as vacuum leak from manifold (hole in gasket or rubber hose), also if silicon chip damaged it also will effect output voltage, wire connections of ground or reference voltage can be corroded or loose.