This morning when I drove out of my garage, I noticed the brake light was on solid. I checked the parking brake pedal but it was not engaged. As I started driving, the light started flashing and there was continuous beeping. A quick internet search indicated 3 possible reasons: parking brake cable sticking, the master cylinder reservoir low on brake fluid or the reservoir cap switch being defective. I unplugged the connector to this reservoir cap and the symptoms went away.
I know I can replace the cap assembly for $150+ but being the frugal person that I am, I'm wondering if the switch is a user replaceable item.
Secondly, if I have to replace it, which newer model Toyota/Lexus would have the same reservoir cap for me to buy from a parts recycling business?

 

You are putting the cart before the horse.

Please determine the cause of the problem and then we can suggest solutions.

Salim

 

The most common one is the cap being defective. It's easy to add more brake fluid and check to see if the parking brake is sticking.

 

Soooo.... is the brake fluid level OK?

 

So here's the troubleshooting I did:
1- Checked parking brake. Pedal goes down about 6 clicks and it works - brake applies when engaged, no braking when released.
2- Looked for the parking brake cable sticking. Couldn't find either end sticking. (visual inspection without getting under the car).
3- Checked brake fluid level. It is full.
4- Disconnected reservoir cap cable from harness. Light flickering and beeping stopped.

This led me to suspect the problem may be with the float or the switch in the cap. I may be wrong and will appreciate additional troubleshooting advice.

 

Parking brake pedal activates a switch. There is no mechanism that looks for binding. You have to ensure that when released the pedal moves sufficiently high to activate the switch. You can assume the astronaut position and depress the parking brake and fiddle with the switch. Similarly you can open the master cylinder cap and physically slide the flat to see if ti makes a difference in the display.

Salim

 

Pull the cap off and check to see if the stem holding the float is loose. If so, push it back into the cap. It should snap in easily. This will stop that annoying alarm.

 

There is another thread about this same problem, rmk. It drove me crazy! A new brake reservoir cap for about $100 solved the problem. If you know anyone with another RX300, I would swap caps temporarily to see if that solves it. Good luck!

 

Parking brake has anything to do with brake light??? Parking light and brake light is two different thing. Was fluid level low? Probably the sensor is optical kind.
Try to clean dirt build up on the sensor.

 

The light being discussed is the "warning light" in the instrument cluster.

Salim

 

Yes, and if I remember correctly, the warning light and chime both activate if you drive with the parking brake engaged. Salim, you can probably tell me if I have that right or not.

 

I didn't see a sensor so not sure where to clean. I have only one BRAKE light for both the Parking brake and brake fluid level.
The light I'm referring to is the BRAKE light. It turns on when parking brake is engaged or the brake fluid in the master cylinder is low. In my case it is also turning on while the parking brake is released and I am driving. The light flickering and accompanying chime keep going on even when the car is stopped at an intersection. The only way to turn these off is to disconnect the reservoir cap switch.
I opened the master cylinder reservoir and there's nothing loose. The float moves without obstruction and the BRAKE light goes on when the float is manually moved down.Unless the experts here think otherwise, it's looking like a bad switch in the reservoir cap. so back to my original questions:
1- Is the reservoir cap switch a user replaceable item?
2- If I have to replace it, which newer model Toyota/Lexus would have the same reservoir cap for me to buy from a parts recycling business?

 

Found a very useful thread with the same issue. All indications are the problem being in the reservoir cap float sensor.
Taking Salim's advice in that thread, I'm going to have brake fluid flushed so the car gets all new brake fluid. The old fluid in the reservoir make have become gummy, making float movement problematic.