What is checked about O2 sensors other than presence?

• A. Electrical resistance of the wiring only.
• B. Temperature reading.
• C. Sensor color.
• D. Proper mounting and secure wiring; no signs of tampering.

Answer: (D)

Beyond simply confirming an O2 sensor is present, a visual inspector checks that the sensor is properly mounted and the wiring is secure with no signs of tampering. This matters because loose or damaged wiring, improper mounting, or tampering can cause inaccurate readings, exhaust leaks, or sensor failure, which can lead to incorrect emissions results or engine problems. The other ideas—checking the electrical resistance of the wiring, reading a temperature value, or judging by the sensor’s color—aren’t reliable visual checks in the standard inspection. Temperature isn’t something you can verify by sight, color isn’t a dependable indicator, and resistance testing requires tools, not a visual check.