DTC Troubleshooting: B1931
DTC B1931: Backup Control Unit No Response
DTC Description
DTC
B1931 Backup Control Unit No Response
  

1.
Problem verification:

Problem verification
?1.
Clear the DTCs with the HDS.


?2.
Open the driver's window all the way down, and close all the doors, then press the engine start/stop button to select the OFF mode.

?3.
Remove all the keyless remotes from inside the vehicle. Hold one keyless remote outside of the opened driver's window at least 8.0 in (20 cm) away from the vehicle.

?4.
With holding the keyless remote outside of the opened driver's window, press the engine start/stop button, and wait for 30 seconds. Repeat this procedure a total of 5 times.

?5.
Check for DTCs with the HDS.
DTC Description
DTC
B1931 Backup Control Unit No Response
  

Is DTC B1931 indicated?

     
YES
     
     
     
Go to step 2.
     
NO
     
     
     
Intermittent failure, the system is OK at this time. Check for loose or poor connections.?
2.
Connector check:

Connector check
?1.
Press the engine start/stop button to select the OFF mode.

?2.
Check for loose connections in the engine start/stop switch 10P connector.

Is the connection OK?

     
YES
     
     
     
Go to step 3.
     
NO
     
     
     
Repair the poor connection of engine start/stop switch 10P connector, and then recheck the system.?
3.
Backup control unit SS1 (+), SS2 (-) lines check:

Backup control unit SS1 (+), SS2 (-) lines check
?1.
Disconnect the following connector.

?2.
Press the engine start/stop button to select the ON mode.

?3.
Measure the voltage between test points 1 and 2.
Test condition
ON mode
Keyless access control unit connector B (28P): disconnected
Test circuit
SS1(+), SS2 (-)
Test point 1
Keyless access control unit connector B (28P) No. 8 (GRN)
Test point 2
Keyless access control unit connector B (28P) No. 12 (BLU)


Is there battery voltage when the engine start/stop button is pressed?

     
YES
     
     
     
Go to step 5.
     
NO
     
     
     
Go to step 4.
4.
Engine start/stop switch check:

Engine start/stop switch check
?1.
Press the engine start/stop button to select the OFF mode.

?2.
Test the engine start/stop switch.

Is the switch OK?

     
YES
     
     
     
Repair an open or high resistance in the wire.?
     
NO
     
     
     
The SS1 (+) and SS2 (-) wires are OK. Replace the engine start/stop switch.?
5.
Engine start/stop switch SS SW VCONT line check:

Engine start/stop switch SS SW VCONT line check
?1.
Press the engine start/stop button to select the OFF mode.

?2.
Reconnect the follwing connector.

?3.
Press the engine start/stop button to select the ON mode.

?4.
Measure the voltage between test points 1 and 2.
Test condition
ON mode
Engine start/stop switch 10P connector: connected
Test circuit
SS SW VCONT
Test point 1
Engine start/stop switch 10P connector No. 7 (PUR)
Test point 2
Body ground


Is there battery voltage?

     
YES
     
     
     
Go to step 6.
     
NO
     
     
     
Go to step 8.
6.
Shorted wire check (DIN/DOUT, DCK lines):

Shorted wire check (DIN/DOUT, DCK lines)
?1.
Press the engine start/stop button to select the OFF mode.

?2.
Disconnect the following connectors.

?3.
Check for continuity between test points 1 and 2 individually.
Test condition
OFF mode
Keyless access control unit connector B (28P): disconnected
Engine start/stop switch 10P connector: disconnected
Test circuit
DIN/DOUT
Test point 1
Keyless access control unit connector B (28P) No. 24 (LT BLU)
Test point 2
Body ground

Test circuit
DCK
Test point 1
Keyless access control unit connector B (28P) No. 23 (WHT)
Test point 2
Body ground


Is there continuity?

     
YES
     
     
     
Repair a short to ground in the wire.?
     
NO
     
     
     
The DIN/DOUT and DCK wires are not shorted. Go to step 7.
7.
Open wire check (DIN/DOUT, DCK lines):

Open wire check (DIN/DOUT, DCK lines)
?1.
Check for continuity between test points 1 and 2 respectively.
Test condition
OFF mode
Keyless access control unit connector B (28P): disconnected
Engine start/stop switch 10P connector: disconnected
Test circuit
DIN/DOUT
Test point 1
Keyless access control unit connector B (28P) No. 24 (LT BLU)
Test point 2
Engine start/stop switch 10P connector No. 9 (LT BLU)

Test circuit
DCK
Test point 1
Keyless access control unit connector B (28P) No. 23 (WHT)
Test point 2
Engine start/stop switch 10P connector No. 10 (WHT)


Is there continuity?

     
YES
     
     
     
The DIN/DOUT and DCK wires are OK. Replace the keyless access control unit.?
     
NO
     
     
     
Repair an open or high resistance in the wire.?
8.
Shorted wire check (SS SW VCONT line):

Shorted wire check (SS SW VCONT line)
?1.
Press the engine start/stop button to select the OFF mode.

?2.
Disconnect the following connectors.

?3.
Check for continuity between test points 1 and 2.
Test condition
OFF mode
Keyless access control unit connector B (28P): disconnected
Test circuit
SS SW VCONT
Test point 1
Keyless access control unit connector B (28P) No. 25 (PUR)
Test point 2
Body ground


Is there continuity?

     
YES
     
     
     
Repair a short to ground in the wire.?
     
NO
     
     
     
The SS SW VCONT wire is not shorted. Go to step 9.
9.
Open wire check (SS SW VCONT line):

Open wire check (SS SW VCONT line)
?1.
Disconnect the following connector.

?2.
Check for continuity between test points 1 and 2.
Test condition
OFF mode
Keyless access control unit connector B (28P): disconnected
Engine start/stop switch 10P connector: disconnected
Test circuit
SS SW VCONT
Test point 1
Keyless access control unit connector B (28P) No. 25 (PUR)
Test point 2
Engine start/stop switch 10P connector No. 7 (PUR)


Is there continuity?

     
YES
     
     
     
     
NO
     
     
     
Repair an open or high resistance in the wire.?