1.7.8 Diagnosis of electrical faults of the front oxygen sensor

P0130/P0150 (LSVEmax/LSVE2max) 

Lambda control can be disabled only when at least a pending fault code (service $07) has been entered in the fault code memory. Several operating conditions do exist under which faulty components can be pinpointed only after a time delay. Lambda control must however be disabled when fault symptoms are detected.

This diagnostic function (which is identical for both banks) sets a general electrical fault. The actual fault which is accompanied by a second entry into the fault code memory is then pinpointed afterwards by the appropriate diagnostic function. This second fault entry could either be a sensor line error or a heater fault of the front oxygen sensor (HO2S). In order to ensure timely MIL illumination (two-in-a-row principle) the general electrical fault is also set when a sensor line error or a heater fault of the front oxygen sensor is set. A general electrical fault LSVEmax of the front heated oxygen sensor will be set when at least one of the following conditions is fulfilled:

• The internal resistance of the oxygen sensor's Nernst cell is implausibly high or the ceramic temperature of the front HO2S is implausibly low. All of the following monitoring conditions must be fulfilled in both cases:
  • The exhaust gas temperature model must be valid.
  • The modeled exhaust gas temperature at the front oxygen sensor's hexagon lies above a calibrated minimum.
  • No fuel cut-off.
  • The front oxygen sensor's heater diagnostic has not been inhibited as a result of a faulty voltage supply.
  • The front oxygen sensor is ready for operation.
  • No malfunction of the front oxygen sensor's heater power stage.
  • No malfunction of the front oxygen sensor's evaluation IC.
  • No short circuits in the front oxygen sensor's circuitry.
• The front oxygen sensor's galvanic (Nernst) voltage line diagnostic is performed via its IC diagnostic and an interruption of that line is detected.
• The front oxygen sensor's virtual ground line diagnostic has been performed via its IC diagnostic and an interruption of that line is detected.
• The front oxygen sensor's heater circuit diagnostic is performed and a heater fault is detected.
• The heating power of the front oxygen sensor is too low.