differential AUDI A4 1999 B5 / 1.G AFC Engine Oxygen Sensor Control Checking Workshop Manual

24-42
If the voltage does not fluctuate, or the sensor responds too slowly (lazy), the following conditions are possible causes:

Slits or holes in the oxygen sensor tip are plugged
Sensor was thermally overloaded
Sensor damaged via silicone contamination (various sprays)
Sensor was lead poisoned with fuel containing lead. Check for lead content using a "PLUMBTESMO" test strip
Terminal resistance in the signal wire
Oxygen sensor too cold-oxygen sensor heater does not function and sensor does not reach ideal operating temperature
Oxygen sensor control switched off (fuel injection system malfunctions stored in DTC memory)
Oxygen sensor damaged with electrical contact cleaner (or equivalent). The spray is drawn in through the signal wire via
capillary action resulting from pressure differential and temperature fluctuation and ends up coating the sensor element
and air passages causing reduced sensitivity or control failure.
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