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.
Component description for a O2 sensor - GF07.04-P-6100T
ENGINE 642.920 in MODEL 211.020/220/620, 219.322
ENGINE 642.921 in MODEL 211.084/089/284/289
ENGINE 642.920 in MODEL 211.022 except CODE (494) USA version
ENGINE 642.920 in MODEL 211.022/222 except CODE (498) Japan version
Shown on model 211.0 up to 31.5.06
Location
The O2 sensor upstream TWC is located at the front in the oxidation catalytic converter, behind the turbocharger.
Task
The O2 sensor upstream TWC detects the residual oxygen content in the exhaust and passes on an appropriate signal to the CDI control unit (N3/9).
Design
The O2 sensor used upstream TWC is designed as a wideband oxygen sensor. The wideband oxygen sensor consists of a pump cell, a concentration cell and a heating element. The heating element maintains the temperature of the ceramic probe body constant at 780°C. The conductivity of the ceramic probe body is temperature-dependent.
Function
Via a small gas entry hole in the pump cell, the exhaust gas reaches the measuring chamber of the concentration cell.
The oxygen from the exhaust is pumped into a reference chamber which serves as the oxygen reference. By application of a voltage to the platinum electrodes of the pump call. oxygen can be pumped into or out of the reference chamber. An evaluation module in the CDI control unit regulates the voltage applied to the pump cell so that the mixture composition in the measuring chamber is continuously adjusted to the value λ = 1. In the case of lean exhaust gas the pump cell pumps oxygen out of the measuring chamber. The pump flow is thus positive. If, however, the exhaust gas is rich, then oxygen at the platinum electrodes is pumped via the catalytic decomposition of carbon dioxide (CO2 ) and water out of the ambient exhaust gas into the measuring chamber. The pump flow is thus negative. If λ = 1 is available in the measuring housing, oxygen must not be transported. In this case the pump flow = 0 mA. The respective required pump flow is the measurement for the oxygen:air ratio and is processed in the CDI control unit for the corresponding functionality.
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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.