04 Toyota 4Runner Brake Light Issue

I own a 2004 toyota 4runner. I am getting a P0504 code on my OBD2 sensor. My brake light comes on sporadically when I accelerate from a stop. It tends to be on more frequently when the car is still cold and when the weather is colder. All of my brake lights work like normal with no flickering, my car drives like normal and I don’t notice any issues. I have replaced the brake switch and checked all of the fuses. All of the fuses seem to be in working order and the new switch didn’t change anything. The VSC Trac, VSC OFF lights have both been on since I got the vehicle a year and a half ago but it doesn’t impair my driving at all. There is no check engine light on either. What am I likely dealing with here?


You are dealing with the facts that a) you were willing to purchase this vehicle with an inoperative stability control,and b) continued to drive it that way for over a year.

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I guess if I had that problem my first step would be to get on my hands & knees, door open & carefully inspect the brake pedal area with a bright flashlight. I’d be especially looking for a cracked or loose electrical connector, or something amiss in the brake pedal linkage, whatever moves when you press on the brake pedal, like a failing bushing, broken support rod, etc.

On some cars the dashboard brake warning light is designed to turn on also for other-than-brake-related reasons. On my 30 year old Corolla IIRC it turns of if the alternator fails. I think the idea is the brake warning light provides a fail-safe in case the alternator is starting to fail and the alternator dash warning light has burned out. Probably not the case with OP’s car, but something to consider anyway.

When checking the actual brake lights at the rear of vehicle, be sure to check all three, the two at each side, and the single high-mounted brake light. If problem continues, no joy, ask friend to drive behind you in their car, on a short trip, looking for anything unusual happening with your car’s brake lights. Check brake fluid level too.