USB Autoscope

Analytics and diagnosctic equipment for automotive industry

O2 sensor

The Zirconia Lambda sensor which is by far the most common narrow band sensor is used to determine the air/fuel ratio in the combustion chamber by reading the oxygen demand of the residual exhaust gas. The sensor tip is made of catalytic material, is hot, and is subject to hot exhaust gas. This exhaust gas may contain some unburned or partially burned fuel if the air/fuel ratio in the combustion chamber is “rich”. To complete the combustion of the unburned or partially burned fuel in/at the catalytic material at the hot sensor tip, additional oxygen is needed. This additional oxygen travels through the membrane at the sensor tip and causes a potential (voltage) difference to develop. This voltage potential is then read by the computer and interpreted as a rich condition. If the air/fuel ratio in the combustion chamber is “lean”, no additional oxygen is needed and a voltage potential does not develop. This low voltage condition is interpreted by the computer as a lean condition.
A very rare sensor is the Titania sensor. This sensor is a true oxygen sensor and it varies it’s resistance according to the oxygen content in the exhaust stream.
The sensors can be mounted before as well as after the catalytic converter.
Application:

  • narrowband lambda sensor;
  • wideband lambda or air/fuel ratio sensor.

o2_sensor_1

o2_sensor_3

Output voltage waveforms from a properly functioning zirconia narrowband lambda-sensor and power supply sensor heater.
1 – signal from a lambda sensor mounted before the catalytic converter;
2 – the power supply for the sensor heater.
A – engine start;
B – running at idle; the sensor is not hot enough to function properly;
C – the sensor is hot enough to start working;
D – start of smooth throttle valve opening;
E – closing of throttle valve.

o2_sensor_2

Engine running at idle.

o2_sensor_4

Engine running at high RPMs.

o2_sensor_5

o2_sensor_7

Output voltage waveforms from a properly functioning zirconia narrowband lambda-sensor and control voltage of sensor heater.
1 – signal from lambda-sensor mounted before the catalytic converter;
2 – PWM control signal for the the sensor heater.
A – engine start and running at idle;
B – the engine control unit increased the duty cycle of the sensor heater;
C – the sensor is heated sufficiently to work properly;
D – start of smooth throttle valve opening;
E – closing of throttle valve.

o2_sensor_6

Engine running at idle.

o2_sensor_8

Engine running at high RPMs.

o2_sensor_9

Engine running at high RPMs.

o2_sensor_10

Output voltage waveforms from a properly functioning zirconia narrowband lambda-sensors.
1 – signal from lambda-sensor mounted before the catalytic converter;
2 – signal from lambda-sensor mounted after the catalytic converter.
A – engine start and running at idle;
B – start of smooth throttle valve opening;
C – closing of throttle valve.

o2_sensor_11

Engine running at idle.

o2_sensor_12

Engine running at high RPMs.

o2_sensor_13

Sharp throttle closing at 3000 RPM.

o2_sensor_14

Output voltage waveform from a malfunctioning lambda-sensor mounted before the catalytic converter. The reaction rate of the sensor is very slow, signal amplitude is low.
A – engine start and running at idle;
B – sensor heated and starts to work.

o2_sensor_15

Engine running at idle.

o2_sensor_16

Sharp throttle closing at 3000 RPM.

o2_sensor_17

Output voltage waveform from a malfunctioning zirconia narrowband lambda-sensor. The sensor is not working.
A – engine start and running at idle;
B – start of smooth throttle valve opening;
C – deceleration and running at idle;
D – snap throttle.

o2_sensor_18

o2_sensor_19

Output voltage waveform from a malfunctioning lambda-sensor. The malfunction causes the sensor to output a negative voltage.
A – engine running at idle;
B – turning off the fuel injectors during deceleration after snap throttle;
C – turning on the injectors at the end of deceleration.

o2_sensor_20

Typical output voltage waveform from a properly functioning narrowband titanium oxide lambda-sensor.
A – engine start;
B – sensor heated and starts to work.

o2_sensor_21

Engine running at idle.

o2_sensor_22

Engine running at high RPMs.

o2_sensor_23

o2_sensor_25

Voltage waveforms from wires of wideband lambda sensor BOSCH LSU (VW Golf 1.6 2003).
1 – black wire;
2 – yellow wire;
3 – red wire;
4 – calibration resistor;
5 – white wire.
A – engine start and running at idle;
B – snap throttle;
C – deceleration;
D – engine shut off.

o2_sensor_24

Voltage waveform of the measurement cell and current of the pump cell of wideband lambda sensor BOSCH LSU, received in differential measuring mode.
1-2 – output voltage of the measurement cell;
3-4 – voltage drop on calibration resistor of the sensor.

The USB Oscilloscope program is required for waveform playback. Get the latest USB Oscilloscope program here.