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P0504 after replacing brake switch, what to test next?

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Hey, long time reader, first time poster here.   Thanks for all the helpful advice so far!  Apologies if this is answered somewhere else, there seem to be a lot of similar cases, but I couldn't find exactly my situation.

I've got a '04 RX330 with the brake lights, VSC, tire pressure, etc...  on the dash.  I went ahead and replaced the brake light switch and the lights went away for about a day, and then they came back.  I then replaced it again with a different switch, and again, the lights went away for a day and came back.   (I tried both the bigger blue switch and the smaller white switch)

Both times, I pulled a P0504 code over OBD2 and I cleared it both times.  Both times that code came back.   

Other diagnostics:

  • I tested both switches with my multimeter, they both seem fine
  • I measured 12V, (well, 11.7V) across the plug when the key is in the ON position.   
  • I've also tested all my fuses in the box underneath the steering wheel.  
  • The car operates totally fine, it runs.
  • The brake lights turn on as expected (all bulbs are working).

Does anyone have any ideas of what else it could be, or what I may need to replace?

Thanks in advance!

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Hello, James.

This is also recommended:

  • Repairing or replacing wiring harness or connectors that leads to the brake switch or circuit

Sometimes vibration will cause a wire/connector electrical connection to be intermittent.

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Okay, that sounds like a good idea.

I assume that there is some ECU that is reading the switch position, and the fault could be inside that component.  Do you happen to know what/where that component is? 

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