WS3A ECT

General Lab Scope


Signal Name ECT
Voltage/division/range 2 V
Time/division/range 1ms

Draw the pattern below:

Explain the operation of sensor or device using the Graph:
(Use arrows at different points, and describe what happens there)

A = up to 2 V range about 2.1 V at the start.
B = Continuing the voltage dropping 
C = 1.9 V after 1 second 


Explain in detail an electrical fault that would make this unit operate incorrectly
Higher resistance will iscause higher voltage drop, which it gets from the ECU (5 V) will cause the wrong return voltage signal to the ECU.


Explain why this condition would cause this unit to malfunction/Use mathematical equations to back up your explanation.
As the temperature increase of the coolant resistance decrease, and the return voltage signal decrease to 5 v Ie: If the variable resistor R2 is 2500 ohms , and R1 in the PCM is 1000 ohms the total current I = V/R = 5v/3000 ohms =0.0014 Amps.
Therefore the voltage drop VD1 = IR = 0.0014 A*3500 ohms = 3.5 V in variable resistance , and the return voltage is 5 - 3.5 v = 1.5 V
If the resistance in sensor ground increase for example: 1000 ohms so the voltage drop at the resistor will be VD2 = IR   IT  = V/R = 5/4500 = 0.001 A and VD2 = IR = 0.001*1000 = 1V
VD1 = IR = 0.001*2500 =2.5V the voltage drop change i n variable resistor from 3.5V to 2.5V and the ECU will determine the PWM according to this wrong voltage of 2.5V


Using the graph on the previous page (use different color)  draw the pattern that this unit would give with this faulty (include the different points as with the previous pattern)
Explain how this condition would affect the operation of the vehicle?
The graph marked with M is a straight line  there is no change voltage drop , and the engine is in open loop, and urning rich, because he ECU fail to go into close loop. Once the engine is warmed up as it gets strong signal from the ECT because high resistance in the component.