Oxygen Sensors On-Vehicle
The Oxygen sensor is found in the exhaust.
The oxygen sensor has 3 wires.
Colour: - Purpose: -
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This is a Zirconia Switching Sensor
Voltage reaches a peak of 1V
Voltage drops to a low of 0V
Average voltage is 0.5V
These readings are because the oxygen sensor fluctuates in voltage between 0-1V which is used as a signal to tell the ECU how rich or lean the engine is running at.
The signal has 15 cross counts over a 10 second period.
If the signal is not cycling normally then the voltage will not fluctuate and will sit at a fixed voltage, resulting in incorrect information to the ECU.
Watch and record the Oxygen Senor signal pattern at Idle.
Voltage reaches a peak of 0.6V
Voltage drops to a low of 0.1V
Average voltage of 0.275V
Cross counts over 10 seconds is 15
If the signal is not cycling normally then the voltage will not fluctuate and will sit at a fixed voltage, resulting in incorrect information to the ECU.
Make the Oxygen Sensor go Rich.
Voltage reaches a peak of 0.7V
If the signal does not reach a high voltage then the signal will show a low voltage meaning the car is running rich.
Make the Oxygen Sensor go Lean
Voltage drops to a low of 0.14V
If the signal is not going low normally then the voltage signal will be high, meaning the car is running rich.
Measure the response time of the sensor
The sensor took 400ms to go from rich to lean
The Zirconium oxygen sensors use a solid state electrolyte typically fabricated from zirconium oxide stabilized with yttrium oxide. The zirconium oxide probe is plated on opposing sides with platinum which serves as the sensor electrodes. For a zirconium oxide sensor to operate properly, it must be heated to approximately 650 degrees Centigrade. At this temperature, on a molecular basis, the zirconium lattice becomes porous, allowing the movement of oxygen ions from a higher concentration of oxygen to a lower one, based on the partial pressure of oxygen.
This oxygen sensor functions properly. From the data I have collected their is no evidence leading me to believe that this oxygen sensor has a fault. When I did the experiment as to make the car run rich, I opened the throttle a bit and received a voltage reading of 0.781V. When I did the experiment as to make the car run lean, I slowly opened up the throttle and then closed it suddenly, this made the car run lean and I obtained an expected reading of 0.147V. These results tell me that this oxygen sensor can accurately tell the ECU how rich or lean the exhaust is.
Engine Load MAP 0.9 V
Engine RPM RPM 750 RPM
Throttle Angle TPS 9 %
Engine Coolant Temp ECT 85 °C
Intake Air Temp IAT 56 °C
Fuel Inj. Opening Pulse PWM 1.8 ms
Vehicle Speed VSS 0 km/h
Oxygen Sensor 02 0.8 V
Idle Control ICV 265 mA
No fault codes were displayed.
Code Number System Affected Cause of Problem
3 MAP Disconnected Plug
6 ECT Disconnected Plug
7 TPS Disconnected Plug
Engine Coolant Temperature (ECT), Circuit High Input
Throttle Angle (TPS), Low Voltage
Engine Load (MAP), High Voltage
I used the information from the fault codes to help me find the fault visually under the bonnet. I found that the TPS, MAP sensor and ECT sensor plugs had all been disconnected.
I repaired the fault by simply plugging back in the disconnected plugs.
Engine Coolant Temp ECT 85 °C
Throttle Angle TPS 9 %
Engine Load MAP 0.9 V
I then cleared the fault codes by removing the negative terminal of the battery.
I rechecked the fault codes and none were displayed.
Live data is very important when fault finding because the data can visually show you the readings of most of the engine components. This will allow you to quickly find which engine component is showing incorrect readings. You can now go and check that component to see if it is indeed faulty and needs to be replaced.
Parameters when checking live data are very helpful because they can describe symptoms that your car may have, which further assists you in finding a fault. For example, if your ICV showed abnormal readings then that sensors parameter is Fuel Injection Opening Pulse. So if you think about whether your car has been running to lean or to rich lately then you will further suspect the ICV to be the problem because the Fuel Injection Opening Pulse may be held open for to long, or not long enough, resulting in your vehicle running either rich or lean.
A Scan Tool can very easily assist you in fault finding by showing you readings of a lot of your cars components. If these readings show up abnormal or not right then you know where to begin your fault finding.
Fuel Pressure Worksheet
Due to the extremely high flammability of petrol it is always good to know the locations of the two closest fire extinguishers. One was located in the car beside us, and also on the wall in the workshop.
Standard fuel pressure specifications, 32-36PSI
No fuel leaks were found.
Fuel pressure was measured under different conditions:
With Key-On Engine-Off (KOEO): 0PSI, This is expected as no fuel is flowing with the car off.
Idling: 40PSI
Maximum: 70PSI, This was done by clamping the fuel return line.
WOT: 50PSI, This was achieved by disconnecting the plug on the vacuum line.
Residual (Rest) pressure: 41PSI
Fuel Pressure is important to know because it determines how fast the petrol is flowing in your car.
A car with low fuel pressure will run lean. This is beacause less petrol will be sprayed at the injectors over the same opening time, due to the low fuel pressure forcing the petrol to flow slowly through the fuel system.
A car with high fuel pressure will run rich. This is because more petrol will be sprayed at the injectors over the same opening time, due to the high fuel pressure forcing the petrol to flow fast through the fuel system.
A faulty fuel pressure regulator can seize open or closed. Seized open will result in low fuel pressure, and a seized closed fuel pressure regulator will result in high fuel pressure. See above for flow-on effects.
Flash Code Worksheet
A plug is located underneath my glove box. A paper clip needs to be inserted into each of the two pin holes, bridging them together. The check engine light then should begin to flash.
3 MAP Disconnected Plug
6 ECT Disconnected Plug
7 TPS Disconnected Plug
After a visual inspection under the bonnet, I found that the MAP sensor, TPS and ECT sensor plugs were all disconnected.
I easily repaired the faults by reconnecting the disconnected plugs.
I then erased the flash codes by disconnecting and reconnecting the negative terminal on the battery.
After rechecking the flash codes, as expected, their were none to be displayed.
The MAP sensor fault will cause the car to run bad because the ECU does not know how much air is coming into the engine. The confused ECU will then cause bad spray patterns at the injectors, resulting in jerking of the car whilst driving.
The ECT fault will also cause trouble in the fuel system because the ECU will not know how hot or cold the car is so the injection spray pattern will be inconsistent, possible jerking of the car whilst driving may occur.
Incorrect data provided by the TPS is invaluable for proper startup, idle and easy throttle response of the car. These operations are affected when a bad throttle position sensor feeds the wrong data to the car's computer. Syptoms such as bucking and jerking of the car, idle surging and sudden stalling may occur.
Once the fault codes have been found, it can be beneficial to run a full scan tool diagnosis of the car to get further information about the faults that you may be dealing with.
Oscilloscope Patterns Worksheet
Signal Name: RPM (Magnetic, Distributor)
Volt/division: 10V
Time/division: 10ms
The magnetic type RPM sensor uses a magnet to sense notches in the crankshaft or harmonic balancer. As the notch passes underneath, it causes a change in the magnetic field that produces an alternating current signal as displayed above.
Their may be a short in the circuit. This would cause no waveform to be seen because the circuit is not complete. The RPM sensor would have no power to it and not function at all. With this fault caused, the waveform would just show a flat line along the oscilloscope.
With the RPM sensor not functioning at all the vehicle engine may experience cylinder misfires, the CPK may not be providing the computer with accurate information on piston position. If the vehicle hesitates during acceleration, the CPK may not be providing cylinder position data to the computer fast enough to fire the appropriate cylinder to accelerate the vehicle in response to driver input. The most serious indication of CPK malfunction is intermittent start, and eventually no start. When the sensor fails, the computer will register a malfunction code and illuminate the check engine light on the instrument panel.
Signal Name: Alternator Ripple
Volt/division: 188mV
Time/division: 2.1ms
The above waveforms are of analternator ripple. The Alternator produces AC voltage and current. The battery requires DC voltage and current to charge properly. Diodes located within the alternator rectify the AC to DC. However, a small amount of AC can still be present and no harm is done. Problems can develop when alternator diode faults permit unacceptable amounts of AC to pass into the vehicle electrical system.
High voltage from the alternator ripple test could imply an undercharged battery, stalling or rough idle.
Signal Name: Primary Ignition
Volt/division: 20V
Time/division: 2ms
The waveform above shows charging voltage of 14.4V, the voltage then drops to 0V when the ECU earths the primary winding which begins the dwell time (charging time of the primary coil). When the earth is removed, the magnetic field in the coil collapses enducing a back EMF spike of 45V, also creating a spark at the spark plugs. Next is the burn time which is the duration of the spark, followed by oscillations and back to charging voltage.
If the ground at the ECU was shorted, (short to earth), then the ECU will not be able to begin charging of the coil by earthing it. With no charge being built up, no back EMF can be created, resulting in no spark occuring. If no spark occurs then the engine will stop because their is no spark to complete the combustion process.
With a short to earth the waveform displayed will just be a line at charging voltage (14.4V).
Signal Name: Ground Circuit
Volt/division: 0.5V
Time/division: 2ms
This waveform above displays that their is a small amount of voltage/resistance at earth. This earth tested has a voltage of 6mV. This reading tells me that the earth is okay. An earth with 50mV or more is not good. The small spikes shown along the waveform above is just noise and signal interruptions.
Signal Name: MAF sensor
Volt/division: 2V
Time/division: 50ms
The waveform above was recorded as the accelerator was opened quickly. The result is shown above which is that as the throttle is opened, the voltage output signal increases, dependant upon the amount the throttle is opened. This waveform also shows me that as the throttle is opened, more air is entering the engine and seeing as the MAF sensor measures incoming air by mass this assures me that the voltage signal will increase as the throttle is opened because more air by mass is entering past the throttle butterfly.
If the MAF sensor had corroded connections to the ECU then inaccurate voltage readings would be supplied to the ECU. The waveform above would fluctuate and a steady voltage increase as the throttle is opened, will not be seen. If the MAF sensor sends the ECU fluctuating voltage signals then the ECU wont know how much air is entering the engine. The ECU calculates the required fuel based on the measured air flow. With these readings being incorrect the air fuel ratio will not be constant and the car may cycle from rich to lean, causing a bucking and jerking effect whilst driving.
Signal Name: MAP Sensor
Volt/division: 2V
Time/division: 100ms
The waveform above was recorded as the throttle was slowly opened and then slowly closed. The effect can be seen above by, as the throttle is opened, the voltage increases with it. When the throttle is closed again the voltage drops back down with the throttle position. The MAP sensor generates a signal that is proportional to the amount of vacuum in the intake manifold. The engine computer then uses this information to adjust ignition timing and fuel enrichment.When the engine is working hard, intake vacuum drops as the throttle opens wide. The engine sucks in more air, which requires more fuel to keep the air/fuel ratio in balance. In fact, when the computer reads a heavy load signal from the MAP sensor, it usually makes the fuel mixture go slightly richer than normal so the engine can produce more power. At the same time, the computer will retard ignition timing slightly to prevent detonation that can damage the engine and hurt performance.
Anything that interferes with the MAP sensor's ability to monitor the pressure differential may upset the fuel mixture and ignition timing. This includes a problem with the MAP sensor itself, grounds or opens in the sensor wiring circuit, and/or vacuum leaks in the intake manifold or hose that connects the sensor to the engine. All of these electrical problems will cause a rough idle, detonation and rich running.
Signal Name: Secondary Ignition
Volts/division: 4KV
Time/division: 3.4ms
The waveform above displays the actions of the secondary ignition circuit. The waveform above is hard to distinguish all sections of it due to the very high Voltage per division range as the secondary winding back EMF spike on this waveform is 14KV.
The diagram above provides a better view of the secondary waveform and describes each part of the waveform's characteristics.
Primary and Secondary Ignition Patterns
Average Firing Voltage
Average Dwell Time
Average Burn Time
Primary Ignition Pattern
The diagram above emphasizes the high back EMF voltages produced each time the magnetic field collapses.
A stacked display, meaning one waveform stacked against another can help you to diagnose a fault by comparing differences between them.
Average Firing Voltage
Average Burn Time
Snap Acceleration
The above waveform shows the readings spiking up slightly from normal with the snap acceleration I created.
Secondary Waveform Pattern
Dual Pattern Oscilloscope Worksheet
Signal Name: MAP Sensor vs Injectors
Volt/division: 10V
Time/division: 5ms
MAP Sensor: The waveform above was recorded as the throttle was slowly opened and then slowly closed. The effect can be seen above by, as the throttle is opened, the voltage increases with it. When the throttle is closed again the voltage drops back down with the throttle position. The MAP sensor generates a signal that is proportional to the amount of vacuum in the intake manifold. The engine computer then uses this information to adjust ignition timing and fuel enrichment.When the engine is working hard, intake vacuum drops as the throttle opens wide. The engine sucks in more air, which requires more fuel to keep the air/fuel ratio in balance. In fact, when the computer reads a heavy load signal from the MAP sensor, it usually makes the fuel mixture go slightly richer than normal so the engine can produce more power. At the same time, the computer will retard ignition timing slightly to prevent detonation that can damage the engine and hurt performance.
Injectors: The injector waveform above shows, charging voltage, followed by the ECU earthing the injector, pulse width modulation. Next the back EMF is induced by the magnetic field in the injector windings collapsing. The voltage then goes back down to charging voltage.
These two components relate to each other by means of the MAP sensor sending a signal voltage to the ECU providing information of how much air is entering the engine. The ECU must adjust the air/fuel ratio dependant on the MAP readings. If the MAP readings tell the ECU of a high amount of air entering the engine then the injectors will have to spray more to provide more fuel to the mixture.
Signal Time: RPM Sensor vs Injectors
Volt/division: 10V
Time/division: 10ms
Injectors: The injector waveform above shows, charging voltage, followed by the ECU earthing the injector, pulse width modulation. Next the back EMF is induced by the magnetic field in the injector windings collapsing. The voltage then goes back down to charging voltage.
The magnetic type RPM sensor uses a magnet to sense notches in the crankshaft or harmonic balancer. As the notch passes underneath, it causes a change in the magnetic field that produces an alternating current signal as displayed above.
The RPM Sensor generates a signal that the ECU needs to determine the position of the crankshaft and the number one cylinder. This information is necessary to control ignition timing and the operation of the fuel injectors.
If the RPM Sensor were to stop working then the engine would stop all together followed by the injectors shutting down. The working of the RPM Sensor is necessary for the continued working of the injectors.
Signal Time: Oxygen Sensor vs Injectors
Volt/division: 10V
Time/division: 10ms
Injectors: The injector waveform above shows, charging voltage, followed by the ECU earthing the injector, pulse width modulation. Next the back EMF is induced by the magnetic field in the injector windings collapsing. The voltage then goes back down to charging voltage.
Oxygen Sensor: Provides a voltage signal from 0 - 1V to the ECU telling how rich or lean the car is operating. 1V for rich and 0V for lean.
These two components above relate in the way that if the oxygen sensor shows a voltage reading of 0.9V, the ECU will register the engine as running rich. The ECU will then counter this by lowering the injection opening time. The lower amount of fuel being sprayed into the engine will allow the engine to begin running lean.
Signal Name: Ignition Primary vs Injectors
Volt/division: 10V
Time/division: 10ms
Injectors: The injector waveform above shows, charging voltage, followed by the ECU earthing the injector, pulse width modulation. Next the back EMF is induced by the magnetic field in the injector windings collapsing. The voltage then goes back down to charging voltage.
The waveform above shows charging voltage of 14.4V, the voltage then drops to 0V when the ECU earths the primary winding which begins the dwell time (charging time of the primary coil). When the earth is removed, the magnetic field in the coil collapses inducing a back EMF spike of 45V, also creating a spark at the spark plugs. Next is the burn time which is the duration of the spark, followed by oscillations and back to charging voltage.
Injection and ignition relate in the way that the injection process must take place for the ignition process to be worth it. The injectors spray fuel into the combustion chamber followed by the ignition system providing a spark to ignite the fuel that has been sprayed by the injector. These two engine functions hold very similar waveforms to each other.
Injectors: Charging time, open the injector (spray time), back EMF, charging voltage.
Ignition: Charging voltage, coil charging time, back EMF, burn time, oscillations, charging voltage.
The two work in very similar ways as stated by their similarity's shown above.
