Twenty Two Years And Counting.
ChatterBank19 mins ago
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For more on marking an answer as the "Best Answer", please visit our FAQ.Hi There, I have just successfully fixed the sensors on my BMW as follows. If you activate the parking sensors (on my car just engage reverse with the ignition on) and then put your ear to each sensor in turn they make a faint ticking noise. On my car the 4 at the rear all ticked as did the central 2 at the front but the outside ones at the front were silent. After removing the front lower grills and a fog light I could get my hand in and pull the sensors out. For some reason the rubber seal on the connectors had expanded pushing apart the connector which then worked loose and lost contact. The connectors could not be positively reconnected but nothing that a few turns of insulation tape couldn't fix. It now all works fine with 8 ticking sensors.
If this doesn't work then you can pull out all the sensors front and rear and buzz them out with a multimeter on a high resistance setting say 200KOhms. There are 3 pins so you would need to make 6 measurements per sensor to take into account polarity. I tried this approach first on the rear sensors and you do get meaningful readings, I would expect a faulty sensor to give a significantly different set of readings to the rest.
Also check you haven't picked up a parking scrape on one of your sensors or an impact from a stone or something.
good luck.