Oscilloscope Patterns
Below are 7 of the following.
The following five sensors are used for WS3A:
MAP (analogue voltage)
MAF (analogue)
TPS (linear type)
ECT
IAT
These sensors and actuators are used for the general lab worksheet WS3::
Sensors
MAP (digital)
MAF (digital)
TPS (switch type)
RPM (ac magnetic crank or distributor)
RPM (cam or distributor)
RPM (Hall digital crank or distributor)
Oxygen sensor
Actuators:
Injectors (petrol)
Injectors (diesel)
Idle air (digital 2 wire)
Idle air (digital 3 wire, both channels)
Ignition timing control (digital or analogue)
Ignition primary
Ground noise
Alternator ripple
General Lab Scope MAP Sensor
Make: Toyota Model: Corolla 4A Year: 2001
Signal Name Map Analog
Volt/division/range 1
Time/division/range 2ms
This graph of Time vs Voltage is not very detailed as it shows the voltage increasing as the throttle is opened (A)
Then a constant 4.5V at WOT (B)
* The pattern below:
Operation of the sensor the MAP sensor uses a perfect vacuum as a reference pressure. The difference in pressure between the vacuum pressure and the intake manifold pressure changes the voltage signal. The MAP sensor converts the intake manifold pressure into a voltage signal.
This graph show that the MAP sensor signal voltage is highest when the intake manifold pressure is highest and is lowest on deceleration with the throttle closed.* As intake manifold pressure rises, the voltage signal increases.
An electrical fault that would make this unit operate incorrectly is a shorted silicon chip or more commonly a open circuit at PIM connection
This condition would cause this unit to malfunction because without a PIM there is an incomplete circuit and the signal voltage will not change
Use mathematical equations to back up your explanation: 5V -0VD = 5V
See the graph right using a green colour I have drawn the pattern that this unit would give with this fault.
This condition would affect the operation of the vehicle, as the ECU needs to know intake manifold pressure to calculate how much fuel to inject and when to ignite the air/fuel charge. Therefore the ECU will think the Throttle is WOT and increase the injection time and advance the timing.
General Lab Scope TPS (Throttle position Sensor)
Make: Toyota Model: Corolla 4A Year: 2001
Signal Name TPS
Volt/division/range 2V/Div
Time/division/range 100ms
* The patterns below show the TPS under acceleration (A) and deceleration (B) both are smooth and show correct operation.
Operation (right) of the sensor or device: A voltage is supplied to Vcc it passes though the carbon track to E2, then to the ECU and ground.As VTA (signal /return) arm moves up the carbon track the voltage will increases as there is less resistance. The VTA arm is connected to the throttle butterfly and moves as you open the throttle.
IDL is in this case supplied with 12 volts which is switched to earth though the idle switch. NOTE: later model TPS do not have an IDL switch
An electrical fault that would make this unit operate incorrectly would be a worn spot on the carbon track creating a blind spot were no reading is given.
This condition would cause this unit to malfunction by giving a bad output signal
Use mathematical equations to back up your explanation? Signal out = 1... 2....3 ....0....4 Volts
Using the graph above (using a green colour) I have drawn the pattern that this unit would give with this fault.
This condition would affect the operation of the vehicle by cutting the injectors at a certain point on the TPS at a RPM possibly giving the engine symptom of a stall and catch.
General Lab Scope THA (IAT)
Make: Toyota Model: Corolla 4A Year: 2001
Signal Name IAT
Volt/division/range 1V
Time/division/range 10ms
 |
| Voltage vs Time |
The pattern below: show the requested line at 2V this shows a constant temperature over 1 second to see a better graph we will plot temperature against Resistance.
 |
| Air temp graph |
Operation of the sensor or device: This is a NTC (negative temperate coefficient) sensor and works as the air temperature is heated the resistance decreases and voltage can increase this voltage is the signal voltage and varies form 5V down to 0.5V
The ECU looks at the coolant signal before it leaves the ECU; usually a 5 volt supply is used.
Because of volt drop the ECU can calculate the temperature at the sensor. Two resistors in
serious must drop all the voltage across them. If the second resistor is larger more voltage on a
wire is needed to push the electrons across the second resistor, if the first resistor is larger more
voltage is dropped across it and the reading at wire A is smaller.
An electrical fault that would make this unit operate incorrectly is a short to earth.
This condition would cause this unit to malfunction this increased resistance will be huge compared to the resistance of the thermistor and ECU, this would result in very low voltage readings at the pin but a reading of near 5V in the earth leakage test
This condition would affect the operation of the vehicle by telling the ECU the air temperature is really cold and the mixture would be alerted accordingly (made rich), giving possible rough running and worse fuel economy.
General Lab Scope ECT or THW
(Thermistor Water)
Make: Toyota Model: Corolla 4A Year: 2001
Signal Name THW
Volt/division/range 2
Time/division/range 10ms
As above The pattern below shows the requested line at 2V this shows a constant temperature over 1 second to see a better graph we will plot temperature against Resistance.
 |
| water temp graph |
Operation of the sensor or device: This is a NTC (negative temperate coefficient) sensor and works as the water temperature is heated the resistance decreases and voltage can increase this voltage is the signal voltage and varies from 5V down to 0.5V
An electrical fault that would make this unit operate incorrectly is a short across the thermistor.
This condition would cause this unit to malfunction by increasing the signal voltage to 5V and telling the ECU the water is hot (80 degrees plus)
/ Use mathematical equations to back up your explanation Change in Resistance = change in constant / temperature.
Using the graph on the previous page (use a different colour) draw the pattern that this unit would give with this fault (include the different points as with the previous pattern) yep.
This condition would affect the operation of the vehicle by telling the ECU the water is hot (80 degrees plus). The ECU will then run the engine rich and rough running may result ) -;
General Lab Scope
Signal Name Primary Ignition
Volt/division/range 20V
Time/division/range 10ms
See the pattern on the right:
The operation of the Primary Ignition in relation to the graph:
A Charging voltage(14.4V)
B Dwell Period There is no current in the coil's primary circuit until the dwell period, this is when the coil is earthed and the voltage seen drops to zero. The dwell period is controlled by the ignition amplifier and the length of the dwell is determined by the time it takes to build up approximately 8 amps. When this predetermined current has been reached, the amplifier stops increasing the primary current and it is maintained until the earth is removed from the coil, at the precise moment of ignition.
C Induced Voltage
The vertical line at the centre of the trace is in excess of 200 volts, this is called the 'induced voltage'. The induced voltage is produced by a process called magnetic inductance. At the point of ignition, the coil's earth circuit is removed and the magnetic field or flux collapses across the coil's windings, this in turn induces an average voltage between 150 to 350 volts The coil's High Tension (HT) output will be proportional to the induced voltage. The height of the induced voltage is sometimes referred to as the primary peak volts.
D The length of the horizontal voltage line is the 'spark duration' or 'burn time', which in this particular case is 1.04 ms.
E Coil Oscillations
The coil oscillation period should display a minimum number of 4 to 5 peaks (both upper and lower). A loss of peaks would indicate that the coil needs substituting for another of comparable values.
General Lab Scope Crank position Magnetic Distrubtor
Signal Name: Magnetic Crank Position
Volt/division/range 2V
Time/division/range 5ms
See the patterns below:
 |
| inductive crankshaft position |
The operation of the sensor or device using the Graph:
In this particular waveform (below) we can evaluate the output voltage from the Crank Angle Sensor (CAS). The voltage will differ between manufacturers, its proximity and engine speed. The main reason for evaluating this waveform is to monitor the output when the engine stops due to a loss of High Tension voltage (HT). The waveform will be an Alternating Current (AC) its voltage will be seen to increase with engine speed. The gap in the picture is due to the ‘missing tooth’ in the flywheel or reluctor and is used as a reference for the Electronic Control Module (ECM) to ascertain the engines position. Some systems use two reference points per revolution.
 |
| inductive crankshaft position |
References
