DTC B1242: Wireless Door Lock Tuner Circuit Malfunction [12/2019 - 11/2023]: Procedure

1. Disconnect the M51 electrical key and tire pressure warning ECU and Receiver connector.
2. Measure the voltage and resistance and check for pulses according to the value(s) in the table below.

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

   *A	For Gasoline Model	-	-
   *a	Component with harness connected (Certification ECU (Smart Key ECU Assembly))	-	-

   Standard Resistance

   Tester Connection	Condition	Specified Condition
   H48-18 (E) - Body ground	Always	Below 1 Ω

   Standard Voltage

   Tester Connection	Condition	Specified Condition
   M5-19 (RDAM) - H48-18 (E)	Always	11 to 14 V
   M5-18 (RCO) - H48-18 (E)	Always	Below 1 V → 4.5 to 5.5 V pulse generation at regular intervals

   Result

   Proceed to
   OK
   NG

Result: 

OK 

REPLACE ELECTRICAL KEY AND TIRE PRESSURE WARNING ECU AND RECEIVER. Refer to  REMOVAL [12/2019 - 11/2023] 

Result: 

NG 

See step  2

1. Disconnect the M5 certification ECU (smart key ECU assembly) connector.
2. Measure the resistance according to the value(s) in the table below.

   Standard Resistance

   Tester Connection	Condition	Specified Condition
   M51-2 (DATA) - M5-19 (RDAM)	Always	Below 1 Ω
   M51-8 (+5) - M5-18 (RCO)	Always	Below 1 Ω
   M51-12 (GND) - Body ground	Always	Below 1 Ω
   M51-2 (DATA) or M5-19 (RDAM) - Other terminals and body ground	Always	10 kΩ or higher
   M51-8 (+5) or M5-18 (RCO) - Other terminals and body ground	Always	10 kΩ or higher

   Result

   Proceed to
   OK
   NG

Result: 

OK 

REPLACE CERTIFICATION ECU (SMART KEY ECU ASSEMBLY). Refer to  REMOVAL [12/2019 - 11/2023] 

Result: 

NG 

REPAIR OR REPLACE HARNESS OR CONNECTOR