The following warning indicates a possible problem in the brake system.
Immediately stop the vehicle in a safe place and contact your Toyota dealer.

If a warning light turns on or a warning buzzer sounds...
Stop the vehicle immediately.Problem Symptoms Table
PROBLEM SYMPTOMS TABLE
HINT:
Use the table below to help determine the cause of problem symptoms.
If multiple suspected areas are listed, the potential causes of the symptoms
are listed in order of probability in the "Suspected Area" ...
Vehicle Speed Sensor "A" Intermittent / Erratic / High (P0503)
DESCRIPTION
If a malfunction (a rapid change in vehicle speed) in the vehicle speed signal
being output from the skid control ECU is detected while the cruise control is in
operation, the ECM determines that there is a momentary interruption or noise, and ...
Inspection
INSPECTION
PROCEDURE
1. INSPECT COURTESY LIGHT SWITCH
(a) Measure the resistance according to the value(s) in the table below.
Standard Resistance:
Tester Connection
Switch Condition
Specified Condition
...