sensors
Input(sensors) → ECU(logic) → Output(solenoids, motors, fan)
Chart of Inputs and Outputs
Measure the signals with a multimeter, set to the right setting, and record in the boxes.
Coolant Temperature (THW or ECT) DC volts | Cold engine 2.5 v | Warmed-up engine 0.403 v |
Throttle Position Sensor DC volts | Closed throttle 0.404 v | Open throttle 3.725 v |
Crank or RPM sensor AC volts and Hertz | Idle rpm 0.952 v / 0.042 kHz | 2500 rpm 2.183 v / 0.082 kHz |
MAP sensor DC volts | Idle vacuum 1.409 v | No vacuum or key on engine off 3.649 v |
Air Temperature (THA or IAT) DC volts | Cold engine 2.398 v | Warmed-up engine 2.089 v |
Throttle Position Switch (Idle and/or WOT) DC volts | Closed throttle 7.43 v | Open throttle 7.18 v |
CAM sensor AC volts & Hertz | Idle rpm 104.4 mv / 0.134 kHz | 2500 rpm 176.5 mv / 0.246 kHz |
Fuel Injector Duty cycle % | Idle 5.7 % | Acceleration 12.6 % |
Idle Air Control Duty cycle % | Idle 66.5 % | Cranking or 2500 55.7 % |
Theory and background
The manifold absolute pressure sensor provides instantaneous manifold pressure information to the engine's electronic control unit (ECU). The data is used to calculate air density and determine the engine's air mass flow rate, which in turn determines the required fuel metering for optimum combustion.
Procedure
To test the MAP sensor voltage, put red meter lead on the signal wire, black lead on a good earth, and dial in DC volts. When I turned the engine key on, engine was running then watched the voltage and recorded the voltage value. Next, engine off but key on and then watched and recorded the voltage again. From the MAP sensor voltage test, I have got results at 1.4 v in idle condition and at 3.6 v in key on (engine off).Procedure
Reflection
When the engine is running with idle condition and key on(engine off), the voltages 1.4 v and 3.6 v are good and will give the ECU the right voltage so it can provide enough fuel for the engine idle at 1.4 v. The higher voltage at 3.6 v can not provide fuel for the engine off. When the throttle is closed or engine idle, the manifold vacuum increases with lower sensor output voltage so the ECU controls less fuel injection. On the other hand, when the throttle is widely opened or engine off, the manifold vacuum decreases with higher sensor voltage and the ECU controls more fuel injection.
If the voltage was higher in the engine idle this would tell the ECU there is lower vacuum. The ECU would give more fuel therefore the engine will run quickly.
2. MAF Sensor (Mass Air Flow sensor)
Theory and background
The air mass information is necessary for the ECU to balance and deliver the correct fuel mass to the engine. Air changes its density as it expands and contracts with temperature and pressure. In automotive applications, air density varies with the ambient temperature, altitude and use of forced induction and this is an ideal application for a mass sensor.
3. Coolant Temperature Sensor
Theory and background
From the coolant temperature sensor test, how the sensor voltage goes up and down with the hot and cold coolant conditions of the engine. It tells the ECU what state of the engine temperature so the ECU can provide the fuel the engine needs under different conditions. If it goes bad, the engine won’t get enough fuel for cold and hot engine conditions. When the engine is cold, the fuel is more injected for optimum combustion. On the other hand, when the engine is hot or warmed-up, the fuel is less injected from ECU's orders.
Procedure
To test the Coolant Temperature sensor voltage, put red meter lead on the signal wire, black lead on a good earth, and the multi meter is placed in a DC volt range. When I turned the engine key on, engine was running and I immediately watched the voltage and recorded the voltage value. Next, the engine was fully warmed up and then I watched and recorded the voltage again. From the coolant temperature sensor voltage test, I have got results at 2.5 v in a cold condition and at 0.4 v in a hot condition.
Reflection
When the engine is cold with the engine starting or after the engine starting condition, the voltage 2.5 v is good and when the engine is fully warmed up and hot, the voltage is dropped significantly to 0.4 v. These will give the ECU the right voltage so it can provide enough fuel for the engine. As a result, when the engine is cold with the higher voltage of the sensor, The ECU orders more fuel injection, however, when the engine is hot with the lower voltage of the sensor, The ECU commands less fuel injection for the appropriate combustion of the engine.
If there was a defect in coolant temperature sensor with the lower voltage of a cold engine this would tell the ECU there is a hot condition. The ECU would order less fuel injection for the cold condition. Therefore, the engine will not be started or run easily from the less fuel injection.
4. Air Temperature Sensor
Theory and background
ECU's orders.
Procedure
To test the air temperature sensor voltage, put red meter lead on the signal wire, black lead on a good earth, and the multi meter is placed in a DC volt range. When I turned the engine key on, the engine was running and I immediately watched the voltage and recorded the voltage value. Next, the engine was warm up fully and then I watched and recorded the voltage again. From the air temperature sensor voltage test, I have got results at 2.4 v in a cold air condition and at 2.1 v in a hot air condition. The difference of voltages was not big due to the air temperatures did not change too much between the cold air condition and fully warmed up.
Reflection
When the air temperatures are cold and hot, the voltages are good at 2.4 v and 2.1 v each. These voltages will give the ECU the right voltage so it can provide enough fuel for the engine. As a result, when the air is cold with the higher voltage of the sensor, the ECU orders more fuel injection, however, when the air is hot with the lower voltage of the sensor, The ECU commands less fuel injection for the appropriate combustion of the engine.
If there was a defect in an air temperature sensor with the lower voltage of a cold air condition this would tell the ECU there is a hot condition. The ECU would order less fuel injection for this condition. Therefore, the engine will not run properly with unstable combustion from the less fuel injection of the cold air condition.
5. TPS (Throttle Position Sensor)
Theory and background
From throttle position sensors, how the sensor voltage goes up and down with the opening and closing of the throttle. It tells the ECU what air to expect coming into the engine so the ECU can provide the fuel the engine needs under different conditions. If it goes bad, the engine won’t get enough fuel.
Procedure
To test the throttle position sensor voltage, put red meter lead on the signal wire, black lead on a good earth, and the multi meter is placed in a DC volt range. To turn on the engine key, when I closed the throttle, I watched the voltage and recorded the voltage value. Next, when the throttle was widely opened, I watched and recorded the voltage again. From this voltage test, I have got results at 0.4 v in a closed throttle and at 3.7 v in an open throttle. The voltage value increased significantly to 3.7 v with wide open throttle.
Reflection
When the throttle is closed and opened, the voltage values are good at 0.4 v and 3.7 v each. These values will give the ECU the right voltage so it can provide enough fuel for the engine. As a result, when the throttle is closed, the sensor produces lower voltage which tells the ECU and then the ECU orders less fuel injection. However, when the throttle is opened, the sensor generates higher voltage it tells the ECU. The ECU commands more fuel injection for the appropriate combustion of the engine.
If there was a defect in TPS with the higher voltage of an engine idle or closed throttle this would tell the ECU which expects more air coming into the combustion chamber. The ECU would order more fuel injection for the open throttle condition. Therefore, the engine will run with higher RPM in an engine idle because of the more fuel injection.
6. RPM Sensor(Cam position sensor, Crank position sensor)
Theory and background
An engine crankshaft sensor provides the signal for crankshaft position and speed (RPM). From this and other sensors the ECU can adjust the ignition timing for optimum conditions.The camshaft sensor tells the ECU which cylinder is firing, so ignition timing can be adjusted for individual cylinders.
Procedure
To test the RPM Sensor AC voltage and frequency(Hz), put red meter lead on the cam or crank position sensor signal wire, black lead on a good earth, and the multi meter is set to a AC volt range. When the engine is idling, I watched the voltage and changed the multi meter range to Hz, then I watched Hz values and recorded. Next, when the engine run at 2500rpm, I measured the AC voltage and Hz again.
From these RPM Sensor AC voltage and frequency(Hz) test, I have got results at 0.952 v and 0.042 Hz in idling and at 2.183 v and 0.082 Hz in 2500rpm. The voltages and frequency are increased significantly when the rpm went up.
Reflection
RPM sensor signal will give the ECU the right voltage and Hz so it can provide enough fuel and right ignition timing for the engine operation. When the engine is idling, the sensors produces lower voltage which tells the ECU and then the ECU orders less fuel injection. However, when the throttle is opened, the sensor generates higher voltage and Hz it tells the ECU. The ECU commands more fuel injection with correct ignition timing for the appropriate combustion of the engine.
If there were faults in RPM sensors with no voltage and Hz the ECU would not order fuel injection for the engine starting. Therefore, the engine would not run. The engine only operates correct cam and crank position for proper ignition timing and fuel injection.
7. Fuel Injector(Output)
Theory and background
The injector is an electromechanical device(output) , which is fed by a 12 volt supply from either the fuel injection relay or the ECU. The voltage is present only when the engine is cranking or running, because it is controlled by the relay or the ECU. The injector is supplied with fuel from a fuel rail. The injector pulse or injection time depend on ECU,s orders which are also related to the input sensor's signals.
Procedure
To test the fuel injector duty cycle %, put red meter lead on the signal wire, black lead on a good earth, and the multi meter is placed in a duty range and trig (-). To turn on the engine key and the engine is running. From the engine idle, I watched the duty value and recorded the duty value. Next, when the throttle was opened and accelerated, I watched and recorded the duty value again. From this duty cycle test, I have got results at 5.7 % in the engine idle and at 12.6 % in the acceleration. The duty cycle increased significantly to 12.6 % in the acceleration which was a almost double of the idle condition.
Reflection
When the engine is running with the idle and the acceleration, the injector duty values are good at 5.7 % and 12.6 % each. These values are given by the ECU signals. When the throttle is opened for the acceleration, the TPS generates higher voltage it tells the ECU. The ECU commands more fuel injection to injectors. Finally, the solenoid valve is opened from the ECU signals and the injectors inject more fuel into intake manifold ports or combustion chambers and then the engine is run with higher RPM. Not only fuel injection is related to TPS, but also the other sensors are connected for the appropriate combustion of the engine.
If there was a defect in an injector the engine would not run properly with idle and higher RPM. If the opening time of the injector was too long the more fuel would be injected and the engine would run with higher RPM or get inappropriate combustion. On the other hand, the opening time of the injector was too short or no fuel injection the less fuel would be injected or there would be no combustion and the engine would run with lower RPM or get unstable combustion.
From the coolant temperature sensor test, how the sensor voltage goes up and down with the hot and cold coolant conditions of the engine. It tells the ECU what state of the engine temperature so the ECU can provide the fuel the engine needs under different conditions. If it goes bad, the engine won’t get enough fuel for cold and hot engine conditions. When the engine is cold, the fuel is more injected for optimum combustion. On the other hand, when the engine is hot or warmed-up, the fuel is less injected from ECU's orders.
Procedure
To test the Coolant Temperature sensor voltage, put red meter lead on the signal wire, black lead on a good earth, and the multi meter is placed in a DC volt range. When I turned the engine key on, engine was running and I immediately watched the voltage and recorded the voltage value. Next, the engine was fully warmed up and then I watched and recorded the voltage again. From the coolant temperature sensor voltage test, I have got results at 2.5 v in a cold condition and at 0.4 v in a hot condition.
Reflection
When the engine is cold with the engine starting or after the engine starting condition, the voltage 2.5 v is good and when the engine is fully warmed up and hot, the voltage is dropped significantly to 0.4 v. These will give the ECU the right voltage so it can provide enough fuel for the engine. As a result, when the engine is cold with the higher voltage of the sensor, The ECU orders more fuel injection, however, when the engine is hot with the lower voltage of the sensor, The ECU commands less fuel injection for the appropriate combustion of the engine.
If there was a defect in coolant temperature sensor with the lower voltage of a cold engine this would tell the ECU there is a hot condition. The ECU would order less fuel injection for the cold condition. Therefore, the engine will not be started or run easily from the less fuel injection.
4. Air Temperature Sensor
Theory and background
ECU's orders.
Procedure
To test the air temperature sensor voltage, put red meter lead on the signal wire, black lead on a good earth, and the multi meter is placed in a DC volt range. When I turned the engine key on, the engine was running and I immediately watched the voltage and recorded the voltage value. Next, the engine was warm up fully and then I watched and recorded the voltage again. From the air temperature sensor voltage test, I have got results at 2.4 v in a cold air condition and at 2.1 v in a hot air condition. The difference of voltages was not big due to the air temperatures did not change too much between the cold air condition and fully warmed up.
Reflection
When the air temperatures are cold and hot, the voltages are good at 2.4 v and 2.1 v each. These voltages will give the ECU the right voltage so it can provide enough fuel for the engine. As a result, when the air is cold with the higher voltage of the sensor, the ECU orders more fuel injection, however, when the air is hot with the lower voltage of the sensor, The ECU commands less fuel injection for the appropriate combustion of the engine.
If there was a defect in an air temperature sensor with the lower voltage of a cold air condition this would tell the ECU there is a hot condition. The ECU would order less fuel injection for this condition. Therefore, the engine will not run properly with unstable combustion from the less fuel injection of the cold air condition.
5. TPS (Throttle Position Sensor)
From throttle position sensors, how the sensor voltage goes up and down with the opening and closing of the throttle. It tells the ECU what air to expect coming into the engine so the ECU can provide the fuel the engine needs under different conditions. If it goes bad, the engine won’t get enough fuel.
Procedure
To test the throttle position sensor voltage, put red meter lead on the signal wire, black lead on a good earth, and the multi meter is placed in a DC volt range. To turn on the engine key, when I closed the throttle, I watched the voltage and recorded the voltage value. Next, when the throttle was widely opened, I watched and recorded the voltage again. From this voltage test, I have got results at 0.4 v in a closed throttle and at 3.7 v in an open throttle. The voltage value increased significantly to 3.7 v with wide open throttle.
Reflection
When the throttle is closed and opened, the voltage values are good at 0.4 v and 3.7 v each. These values will give the ECU the right voltage so it can provide enough fuel for the engine. As a result, when the throttle is closed, the sensor produces lower voltage which tells the ECU and then the ECU orders less fuel injection. However, when the throttle is opened, the sensor generates higher voltage it tells the ECU. The ECU commands more fuel injection for the appropriate combustion of the engine.
If there was a defect in TPS with the higher voltage of an engine idle or closed throttle this would tell the ECU which expects more air coming into the combustion chamber. The ECU would order more fuel injection for the open throttle condition. Therefore, the engine will run with higher RPM in an engine idle because of the more fuel injection.
6. RPM Sensor(Cam position sensor, Crank position sensor)
An engine crankshaft sensor provides the signal for crankshaft position and speed (RPM). From this and other sensors the ECU can adjust the ignition timing for optimum conditions.The camshaft sensor tells the ECU which cylinder is firing, so ignition timing can be adjusted for individual cylinders.
Procedure
To test the RPM Sensor AC voltage and frequency(Hz), put red meter lead on the cam or crank position sensor signal wire, black lead on a good earth, and the multi meter is set to a AC volt range. When the engine is idling, I watched the voltage and changed the multi meter range to Hz, then I watched Hz values and recorded. Next, when the engine run at 2500rpm, I measured the AC voltage and Hz again.
From these RPM Sensor AC voltage and frequency(Hz) test, I have got results at 0.952 v and 0.042 Hz in idling and at 2.183 v and 0.082 Hz in 2500rpm. The voltages and frequency are increased significantly when the rpm went up.
Reflection
RPM sensor signal will give the ECU the right voltage and Hz so it can provide enough fuel and right ignition timing for the engine operation. When the engine is idling, the sensors produces lower voltage which tells the ECU and then the ECU orders less fuel injection. However, when the throttle is opened, the sensor generates higher voltage and Hz it tells the ECU. The ECU commands more fuel injection with correct ignition timing for the appropriate combustion of the engine.
If there were faults in RPM sensors with no voltage and Hz the ECU would not order fuel injection for the engine starting. Therefore, the engine would not run. The engine only operates correct cam and crank position for proper ignition timing and fuel injection.
7. Fuel Injector(Output)
The injector is an electromechanical device(output) , which is fed by a 12 volt supply from either the fuel injection relay or the ECU. The voltage is present only when the engine is cranking or running, because it is controlled by the relay or the ECU. The injector is supplied with fuel from a fuel rail. The injector pulse or injection time depend on ECU,s orders which are also related to the input sensor's signals.
Procedure
To test the fuel injector duty cycle %, put red meter lead on the signal wire, black lead on a good earth, and the multi meter is placed in a duty range and trig (-). To turn on the engine key and the engine is running. From the engine idle, I watched the duty value and recorded the duty value. Next, when the throttle was opened and accelerated, I watched and recorded the duty value again. From this duty cycle test, I have got results at 5.7 % in the engine idle and at 12.6 % in the acceleration. The duty cycle increased significantly to 12.6 % in the acceleration which was a almost double of the idle condition.
Reflection
When the engine is running with the idle and the acceleration, the injector duty values are good at 5.7 % and 12.6 % each. These values are given by the ECU signals. When the throttle is opened for the acceleration, the TPS generates higher voltage it tells the ECU. The ECU commands more fuel injection to injectors. Finally, the solenoid valve is opened from the ECU signals and the injectors inject more fuel into intake manifold ports or combustion chambers and then the engine is run with higher RPM. Not only fuel injection is related to TPS, but also the other sensors are connected for the appropriate combustion of the engine.
If there was a defect in an injector the engine would not run properly with idle and higher RPM. If the opening time of the injector was too long the more fuel would be injected and the engine would run with higher RPM or get inappropriate combustion. On the other hand, the opening time of the injector was too short or no fuel injection the less fuel would be injected or there would be no combustion and the engine would run with lower RPM or get unstable combustion.
Some good information. Glad to see you have started.
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