Oxygen Sensor Signal Influence On Injector "Open" Time

The oxygen sensor controlled air/fuel ratio constantly cycles between lean and rich within a very narrow range (lambda window). This cycling produces a voltage signal from 0.15 (lean) to 0.85 (rich) volts on a Bosch system or changes the voltage drop of the resistive jump oxygen sensors of the Siemens systems causing a voltage swing to occur at the monitoring circuit(s) in the control module.

The voltage swings (hi to low) contain information on the amount of residual oxygen in the exhaust gas. This cycling in the oxygen sensor control circuit is caused by a "dead time" delay. The delay is from the point the fuel is metered to the point at which the exhaust gas is produced and detected at the oxygen sensor in the exhaust system.

The constantly changing oxygen sensor input to the ECM is needed to correct the ms injection time to ensure that the ideal air/fuel ratio is maintained.

Systems with stereo oxygen sensors (M60, M62 and M52-328i), the ECM can also adapt the ms injection time by bank.

The ECM monitors the;
- amplitude of the signal (highest voltage or range sensor is producing)
- switching time of the signal (how fast from lean to rich)
- frequency of complete cycles (how many within a period of time)

These characteristics provide info to the ECM that reflect the overall condition of the sensor.