Inspection Procedure

WARNING: This page is about a different car, the 2004 Lexus SC 430. However, it is still accessible from the selected car via links, so may be relevant.

INSPECT TELEPHONE SWITCH ASSY (MAYDAY SWITCH)
1. Disconnect the telephone switch connector.
2. Check that the continuity exists between each terminals of switch when each switch is pressed.
  
  Fig 1: Tester Specification Table - Mayday Switch
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  
  OK:
  
  There is a continuity when switch is pressed, and no continuity when not pressed.
  
  Fig 2: Identifying Telephone Switch Connector Terminals
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
1. NG: REPLACE TELEPHONE SWITCH ASSY (MAYDAY SWITCH)
2. OK: Go to next step.
CHECK HARNESS AND CONNECTOR (BETWEEN TELEPHONE ECU (MAYDAY ECU) AND TELEPHONE SWITCH (MAYDAY SWITCH) ASSY) (See HOW TO PROCEED WITH TROUBLESHOOTING )
1. NG: REPAIR OR REPLACE HARNESS OR CONNECTOR
2. OK: Go to next step.
  REPLACE TELEPHONE ECU ASSY (MAYDAY ECU)
HINT:

If DTC is not cleared even through the Mayday ECU is replaced, replace the Mayday Assembly (Transceiver, Back-up battery, Bus buffer ECU and Mayday ECU).