DTC B1242 Wireless Door Lock Tuner Circuit Malfunction

DESCRIPTION

The electrical key antenna and the door control receiver are used as antennas for the entry and wireless door lock functions of the entry and start system.

The certification ECU decodes the requested entry and start system operation by identifying a key code based on electric waves received via the electrical key antenna and the door control receiver. The ECU then sends a command, according to the requested operation, to each ECU. (e.g. If door lock operation is requested, the ECU sends a door lock command to the main body ECU RH.)

DTC No.	DTC Detection Condition	Trouble Area
B1242	If the certification ECU detects that terminal RDA or RSSI is short-circuited, this DTC is stored.	Electrical Key Antenna Door Control Receiver Wire harness Certification ECU

WIRING DIAGRAM

Dtc B1242 Wireless Door Lock Tuner Circuit Malfunction. DOOR LOCK. Lexus IS250 IS220d GSE20 ALE20

INSPECTION PROCEDURE

1.CHECK HARNESS AND CONNECTOR (CERTIFICATION ECU - DOOR CONTROL RECEIVER)

Dtc B1242 Wireless Door Lock Tuner Circuit Malfunction. DOOR LOCK. Lexus IS250 IS220d GSE20 ALE20

Disconnect the P33 ECU connector.

Disconnect the P31 receiver connector.

Measure the resistance according to the value(s) in the table below.

Standard resistance:

Tester Connection (Symbols)	Condition	Specified Condition
P33-37 (ASEL) - P31-4 (ASEL)	Always	Below 1 Ω
P33-39 (RSSI) - P31-5 (RSSI)	Always	Below 1 Ω
P33-38 (RDA) - P31-3 (DATA)	Always	Below 1 Ω
P33-29 (RCO) - P31-2 (+5)	Always	Below 1 Ω
P33-37 (ASEL) - Body ground	Always	10 kΩ or higher
P33-39 (RSSI) - Body ground	Always	10 kΩ or higher
P33-38 (RDA) - Body ground	Always	10 kΩ or higher
P33-29 (RCO) - Body ground	Always	10 kΩ or higher

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

2.CHECK HARNESS AND CONNECTOR (DOOR CONTROL RECEIVER - ELECTRICAL KEY ANTENNA)

Disconnect the P20 antenna connector.

Measure the resistance according to the value(s) in the table below.

HINT:

Perform the measurement with the P31 receiver connector disconnected.

Standard resistance:
Tester Connection
(Symbols) Condition Specified Condition
P31-7 (ANT) - P20-1 (ANT) Always Below 1 Ω
P31-7 (ANT) - Body ground Always 10 kΩ or higher

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

3.CHECK AND REPLACE DOOR CONTROL RECEIVER (RECONFIRM DTC)

Replace the receiver.

Clear the DTC and repeat the procedure to re-check for DTCs .

OK:
DTC is not output.

END (RECEIVER IS DEFECTIVE)

NG

4.CHECK AND REPLACE ELECTRICAL KEY ANTENNA (RECONFIRM DTC)

Replace the antenna.

Clear the DTC and repeat the procedure to re-check for DTCs .

OK:
DTC is not output.

END (ANTENNA IS DEFECTIVE)

NG

5.INSPECT CERTIFICATION ECU

Reconnect the P33 ECU connector.

Reconnect the P20 antenna connector.

Reconnect the P31 receiver connector.

Measure the voltage according to the value(s) in the table below.

Standard voltage:

Tester Connection (Symbols)	Condition	Specified Condition
P33-37 (ASEL) - Body ground	Engine switch OFF, luggage compartment door OPEN	Below 1 V
P33-37 (ASEL) - Body ground	Engine switch OFF, luggage compartment door CLOSE	4.6 to 5.4 V
P33-39 (RSSI) - Body ground	Engine switch OFF, all doors closed, the electrical key is not in the action area	10 to 14 V
P33-39 (RSSI) - Body ground	Engine switch OFF, all doors closed, the electrical key in the action area	Below 1 V
P33-38 (RDA) -Body ground	Engine switch OFF, all doors closed and electrical key switch OFF	10 to 14 V
P33-38 (RDA) -Body ground	Engine switch OFF, all doors closed and electrical key switch ON	Pulse generation
P33-29 (RCO) - Body ground	Engine switch OFF, all doors closed and electrical key switch OFF	Below 1 V
P33-29 (RCO) - Body ground	Engine switch OFF, all doors closed and electrical key switch ON	4.6 to 5.4 V

REPLACE CERTIFICATION ECU

PROCEED TO NEXT CIRCUIT INSPECTION SHOWN IN PROBLEM SYMPTOMS TABLE