Toyota Yaris: Smart Key System (for Start Function) / Antenna Coil Circuit Voltage Out of Range (B27841C)

Toyota Yaris XP210 (2020-2024) Reapir and Service Manual / Vehicle Interior / Theft Deterrent / Keyless Entry / Smart Key System (for Start Function) / Antenna Coil Circuit Voltage Out of Range (B27841C)

DESCRIPTION

When an open or short circuit is detected in the transponder key amplifier coil built into the engine switch, the certification ECU (smart key ECU assembly) stores this DTC. This DTC is also stored as a history DTC.

DTC No.	Detection Item	DTC Detection Condition	Trouble Area	Note
B27841C	Antenna Coil Circuit Voltage Out of Range	The transponder key amplifier coil built into the engine switch is open (see below) or shorted (determined by communication with certification ECU (smart key ECU assembly)). (1 trip detection logic*)	Engine switch Certification ECU (smart key ECU assembly) Wire harness or connector	The electrical key transmitter sub-assembly held near the engine switch, an engine start operation is performed by pressing and holding the engine switch when the transmitter battery is depleted.

*: Only output while a malfunction is present.

Vehicle Condition and Fail-safe Operation when Malfunction Detected

Vehicle Condition when Malfunction Detected	Fail-safe Operation when Malfunction Detected
Engine cannot be started when transmitter battery is depleted by holding electrical key transmitter sub-assembly near engine switch and pressing and holding engine switch.	-

Related Data List and Active Test

DTC No.	Data List and Active Test
B27841C	-

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

When using the GTS with the ignition switch off, connect the GTS to the DLC3 and turn a courtesy light switch on and off at intervals of 1.5 seconds or less until communication between the GTS and the vehicle begins. Then select the vehicle type under manual mode and enter the following menus: Body Electrical / Smart Key. While using the GTS, periodically turn a courtesy light switch on and off at intervals of 1.5 seconds or less to maintain communication between the GTS and the vehicle.
The smart key system (for Start Function) uses the LIN communication system and CAN communication system. Inspect the communication function by following How to Proceed with Troubleshooting. Troubleshoot the smart key system (for Start Function) after confirming that the communication systems are functioning properly.
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Before replacing the certification ECU (smart key ECU assembly), refer to Registration.
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After performing repairs, confirm that no DTCs are output by performing "DTC Output Confirmation Operation".

PROCEDURE

1.	CHECK CONNECTION OF CONNECTOR

(a) Check that the connectors are properly connected to the engine switch and certification ECU (smart key ECU assembly).

OK:

Connectors are properly connected.

CONNECT CONNECTORS PROPERLY

2.	CHECK HARNESS AND CONNECTOR (CERTIFICATION ECU (SMART KEY ECU ASSEMBLY) - ENGINE SWITCH AND BODY GROUND)

(a) Disconnect the H46 certification ECU (smart key ECU assembly) connector.

(b) Disconnect the H68 engine switch connector.

Standard Resistance:

Tester Connection	Condition	Specified Condition
H46-12 (ANT1) - H68-1 (ANT1)	Always	Below 1 Ω
H46-12 (ANT1) or H68-1 (ANT1) - Body ground	Always	10 kΩ or higher
H46-13 (ANT2) - H68-7 (ANT2)	Always	Below 1 Ω
H46-13 (ANT2) or H68-7 (ANT2) - Body ground	Always	10 kΩ or higher

REPAIR OR REPLACE HARNESS OR CONNECTOR

3.	CHECK CERTIFICATION ECU (SMART KEY ECU ASSEMBLY)

(a) Connect the H46 certification ECU (smart key ECU assembly) connector.

(b) Using an oscilloscope, check the waveform.

Component with harness connected

(Certification ECU (Smart Key ECU Assembly))

Waveform 1

OK:

Tester Connection	Condition	Tool Setting	Specified Condition
H46-12 (ANT1) - H46-29 (E)	Ignition switch off, electrical key transmitter sub-assembly not in cabin, within 30 seconds of engine switch pressed	20 V/DIV., 200 ms./DIV.	Pulse generation (See waveform 1)
H46-13 (ANT2) - H46-29 (E)	Ignition switch off, electrical key transmitter sub-assembly not in cabin, within 30 seconds of engine switch pressed	20 V/DIV., 200 ms./DIV.	Pulse generation (See waveform 2)

Tester Connection

Condition

Tool Setting

Specified Condition

H46-12 (ANT1) - H46-29 (E)

Ignition switch off, electrical key transmitter sub-assembly not in cabin, within 30 seconds of engine switch pressed

20 V/DIV., 200 ms./DIV.

Pulse generation

(See waveform 1)

H46-13 (ANT2) - H46-29 (E)

Ignition switch off, electrical key transmitter sub-assembly not in cabin, within 30 seconds of engine switch pressed

20 V/DIV., 200 ms./DIV.

Pulse generation

(See waveform 2)

REPLACE ENGINE SWITCH

REPLACE CERTIFICATION ECU (SMART KEY ECU ASSEMBLY)

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