ECU Input and Output Testing

Engine that was used to test sensors. it is a Toyota 4A-FE out of a Carina

Today I completed the ECU Input and output testing. This Involved checking: 

• Battery voltage 
• Coolant temperature sensor 
• Throttle position sensor 
• MAP sensor

All of these tests were done with a multimeter on either voltage AC or DC or on the duty cycle setting. then putting the probes of multimeter into there respective signal ports. 

How Sensors were tested.

To left of picture is the signal board with each sensor that was available to check, on it at each green port.

 in this picture the coolant temperature sensor voltage was being read  1.5V at this time engine was running and not quite at operating temperature.

Results

Battery Voltage: When tested battery showed a voltage of 13.9V when not running and when engine was running 14.2V Which was within specifications because this meant that the alternator was working correctly as voltage across battery should increase to around 14V when running due to alternator regulating voltage correctly. If it was lower or higher there would be a problem with voltage regulator and would need replacing.

Coolant temperature sensor: This showed a voltage of 3.15V when engine was cold and once engine heated up to operating temperature this voltage dropped to 1.2V Indicating it was working correctly, because voltage should drop as engine temperature increases because the sensor contains a wax element which expands when hot this causes resistance to increase and voltage to drop. If voltage did not drop this would mean that the sensor is malfunctioning causing engine to run rich and would need replacing.

Throttle Position Sensor: Voltage of 0.60V was shown when throttle was closed then it increased to 3.85V when throttle was fully open because of resistance decrease. If the resistance had not decreased when the throttle was completely open the ECU would not tell injectors to deliver the correct amount of fuel causing the engine to run lean. drastically effecting engine performance and sensor would need replacing.

MAP Sensor: This showed a voltage of 0.82V when Idling and when engine was accelerating a reading of 0.91V and when throttle was fully open a voltage of 1.78V was shown.  These readings were all correct. If voltage was to low or too high in these different throttle levels this would cause the ECU to receive incorrect signals and the pulse of the injectors would be at wrong intervals effecting the air fuel mixture, effecting engine performance.