Diagnosis of Universal Lambda Sensor - UEGO

Diagnosis of Universal Lambda Sensor - UEGO (911 Turbo)

General Description

Offset
Incorrect lambda measurement due to shunting effects. Diagnosis: Lambda-offset of downstream control exceeds threshold.

Heater Coupling
Low impedance coupling between heater and sensor can cause lambda modulations with the heater pulse rate.

Dynamics - Slow Response
Due to aging the sensor dynamics can decrease. Diagnosis: Comparison of measured and estimated (model-based) lambda-error caused by artificial lambda modulation.

Plausibility
a. Power Stage - Diagnosis:
Output Voltage of the Power Stage will be switched to ≥ 4.775 Volts, if a hardware malfunction has been detected by IC.
b. UEGO (Universal lambda Sensor = LSU) not active:
Diagnosis: lambda LSU is close to 1.0, but downstream sensor indicates lean or rich mixture
c. Sensor current high (lambda LSU lean):
lambda LSU > 1.2 while downstream sensor indicates rich mixture
d. Sensor current low (lambda LSU rich):
lambda LSU < 0.8 while downstream sensor indicates lean mixture

Oxygen Sensor Output Voltage Characteristic Diagram







Monitoring Overview Diagram

Offset:







Heater Monitoring of Universal Lambda Sensor - UEGO (911 Turbo)

Diagnosis

Operation readiness
Time for "operation readiness" after "heater on". Malfunctioning heater will lead to "sensor fault" detection.

Power stage diagnosis
Comparison of control signal (input) with output signal.

Heater Monitoring of Universal Lambda Sensor - UEGO (911 Turbo).

Operation Readiness