LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> BMW >> 1990 >> 325is Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System/Component Tests >> Engine Sensors & Switches >> Oxygen (O2) Sensor
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Oxygen (O2) Sensor

  1. Engine should be at normal operating temperature. Disconnect O2 sensor connector. Clamp vacuum line on fuel pressure regulator so no vacuum signal to pressure regulator).
  2. Start engine. Place gas analyzer probe in tailpipe. Analyzer CO level should read rich condition. Connect O2 sensor connector. CO level should drop to normal level. If CO level does not drop to normal level, O2 sensor or circuit may be defective.
  3. O2 sensor normally operates within a range from .25 volts (lean) to .85 volts (rich). If there is a short or open on O2 sensor connector wires, O2 sensor will output a constant .45 volt value to the MCU.
scientia non olet · About LEMON Manuals