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.
Heated oxygen sensor diagnostics
The front heated oxygen sensor is of the linear type and works with current control. That is why it is not possible to measure the signals from the heated oxygen sensor with a multimeter. The rear heated oxygen sensor is of the binary type and functions as earlier heated oxygen sensors. The engine control module (ECM) checks the heated oxygen sensors when conditions for diagnostics have been fulfilled.
The following faults can be registered by the control module:
- Electrical faults in circuits for the actual heated oxygen sensors (HO2S) and in their preheating
- Adaptation. The control module checks that the long-term fuel trim is not higher or lower than the pre-defined values
- Heated oxygen sensor dynamics. The control module checks that the switch time between rich and lean mixture is not too long.
For further information about diagnostics for the heated oxygen sensor, see "Diagnostic trouble code (DTC) information" in VIDA, information manager.
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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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