how you know which bumper sensor you need to change ????????? im talking on a 04 front bumper. thanks for all your help.



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I've never had one fail to know personally, but just curious if the others continue working but you get a warning light? If so, you could have somebody else cover them up one at a time with a broom or something from beside of the car.

 

I have bad sensor too. When trying to activate the PA, it won't work. It'll only beep and tell you of the bad sensor.

 

Note: there are two sensor sizes. The two next to the license plate is different than the outers, so if you do find which one, replace accordingly.

First check to see if the lens of the sensors are dirty. Just wipe clean and try again.

 

You can check resistance of each sensor individually, from the system cable connector on the radiator support (IIRC raise hood and remove black trim piece inboard/below Drivers side headlight to expose the multiwire connector.) Spec calls for 10 ohm resistance (again IIRC, but you can make comparative readings easily and look for the odd resistance.)
But, that test can be inconclusive. Last time I needed one, the bad sensor was perfect in apperance, and checked at textbook ohms. That became a swap and test exercise to isolate the bad sensor. It's a lot of work: you must remove the bumper cover to get access; but you're gonna remove the cover anyway to replace any sensor.
Also that time, my Toyota dealer's diagnostic computer said "inconclusive".