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.

Oscilloscope Patterns to Capture WS3B (two channels)

This is a pattern of injector against MAP sensor. Where we can see when engine load increases it will increase injector open time. So with more RPM's injector must open more often and for a longer time. If MAP sensor not working properly it will create a miss fire and rich or lean burn in the engine, which cause high emission and bad fuel economy. Engine can have a flat spots in acceleration and perform not well.

RPM sensor and injector. Common thing in both of them is that they start to open and ignite spark plug faster with increase of RPM's, so frequency increases. If injector not working properly or fuel pressure is low or high, it will make engine misfire or have a flat spots in acceleration. Same as spark plugs ignites at the wrong time they can cause detonation in the engine and damage it.



Oxygen sensor and injector by making engine goes rich we make injector open more often and for longer. And in the same time oxygen sensor reads rich combustion.



Primary ignition and injector.












All this test has been done on a Toyota Corolla 4AFE engine, and from this test we can see which component doesn't work properly by matching it against the other component pattern. When one of the component works with errors it can effect the others.

Oscilloscope Patterns to Capture WS3A

Oxygen sensor.

Its a sensor that adjust air to fuel ratio when engine in a closed loop. It riches and leans fuel mixture by opening injectors longer or shorter.

This is a cycle of oxygen sensor, when engine on idle and in closed loop it cycles to make emission less, so we can breath fresh air. If this sensor is old, it can be blocked by exhaust gases and give wrong reading and make the car run rich when it should be lean. Also if wires are corrupted with oxidation, it also can give a wrong signal, if we add extra resistance in the plug of the sensor it will affect the output signal of the sensor. So the ECU can always think that its running lean and add extra fuel and make the engine run inefficient by using extra petrol, even black smoke can be visible from exhaust if its so bad.

This is Toyota idle control valve, Regulates idle depending on engine temperature, problem when siezed up ether on cold start -high idle or cold start hot idle. Can be cleaned and work back as factory. If it seized up when its in hot mode it will have high RPM's even when engine fully warmed up above 1200 RPM's constantly, or when its stuck in warm position, the car wont have cold start idle. So this thing helps to get engine to warm up or closed loop mode faster by adding more air on idle. When this vale malfunction it will take longer time on idle to get to closed loop, so emission would be increased.

Fuel injector. This thing supply engine with fuel (petrol or diesel). It remains closed and opens only when fuel needs to be injected, fuel keeps under pressure in the fuel line. Could cause problem when starts dripping fuel or high resistance created in trigger (ground wire) by opening them for shorter period. May cause bad performance on high and low RPM's. They can be clean to give more performance when old, but needs to be replace as non fixable item.

Here is a MAP sensor or engine load sensor. Wave for on oscilloscope shows when engine accelerating wave going up increasing voltage and decelerating wave going down voltage low, better then air flow meter as last longer. It has got 5 volts supply, ground and signal output for ECU. Ef any of wires got high resistance it will effect the sensor output and make the engine runs bad.

TPS sensor. On a graph we can see switch type. Down the bottom of the graph is a 0 volts and when it fully open it read about 12 volts and give ECU signal to spray more fuel as car in fast acceleration mode. For automatic car it also will change gear to the lowest possible one.

Air flow meter, that the sensor which can kill your engine or ether run it properly! On a graph we can see when throttle open and more air gets inside intake manifold it changes voltage output straight away and from 0.2 volts it reads above 4 volts. How does it happened? Magic or something else? It hag got platinum wire and a thermistor wire connected to OP-AM with a Winston bridge. Op-am looks at the signal output and multiples it for ECU to read. With the output signal ECU can determine how much petrol to inject for better combustion and fuel economy. If we increase resistance in platinum wire lets say because of oxidation, it will effect the out put signal and instead of running normal engine can run rich and use more fuel and produce more emission. So this sensor is critical for fuel economy and good performance as running rich doesn't mean running good!

CMP sensor, the car wont have a spark without this sensor and wont even start. Its important for ECU to know at which stroke number 1 cylinder and the rest 3 cylinders.