An oxygen or lambda sensor provides exhaust-gas feedback to the engine-control system. An upstream sensor supports fuelling control; a downstream sensor commonly monitors catalyst operation. The number and position of sensors depend on the engine and exhaust layout.
A narrowband sensor mainly indicates rich or lean operation around stoichiometric combustion. A conventional zirconia sensor switches roughly between 0.1V and 0.9V and is unsuitable for measuring a broad air-fuel range.
A wideband system uses a sensing cell, pump cell and controller. The controller manages the heater and pump current, then provides data to an ECU or gauge, for example through an analogue signal or CAN. A sensor alone cannot supply a calibrated wideband reading without the appropriate control electronics.
Bosch LSU 4.2, LSU 4.9 and LSU 4.9 MINI, and NTK wideband sensors require compatible controllers. Check the specific sensor and controller documentation rather than assuming interchangeable wiring or calibration. Heater control, mounting position, temperature and exhaust pressure affect installation and measurement.
For tuning, use the appropriate sensor and log its reading alongside the other engine data. A rich or lean indication needs interpreting with the operating conditions, fuel supply, ignition and any air or exhaust leaks. Refer to the linked Bosch datasheets for model-specific limits.
