Usually around 100k miles...At $35 if you have any thought that it could be original, I'd replace it. If it is getting old the refresh rate could be slowing. You can always probe it and see whats going on although it may be easier just to replace it.

1990 Mustang GT Bosch sensor ~$35.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k