Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
1990 BMW 325is AutomaticFACTORY OEM SERVICE PROCEDURE
Oxygen (O2) Sensor
- 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).
- 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.
- 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.
Factory Service Tools
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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