DTC : B1931

DTC B1931  : Backup Control Unit No Response

DTC (Backup Control Unit)

NOTE:  If you are troubleshooting multiple DTCs, be sure to follow the instructions in B-CAN System Diagnosis Test Mode A - Refer to:

Body Electrical Troubleshooting - B-CAN System Diagnosis Test Mode A - Initial Communication and DTC Checks .

1. Problem verification

   -1. Clear the DTCs with the HDS.

   Clear DTCs

   - 2. Open the driver's window all the way down, and close all the doors, then turn the vehicle to the OFF (LOCK) mode.

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

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

   -1. Turn the vehicle to the OFF (LOCK) mode.

   - 2. Check for loose connections in the engine start/stop switch 12P connector. Engine Start/Stop Switch - Removal and Installation

   Is the connection OK?

   YES 

   Go to step 3.

   NO 

   Repair the poor connection of engine start/stop switch 12P connector, and then recheck the system.

3. Keyless access/TPMS control unit SS1+, SS2- lines check

   -1. Disconnect the following connector.

   Keyless access/TPMS control unit connector B (36P)

   - 2. Connect terminals A and B with a jumper wire.

   Terminal A	Keyless access/TPMS control unit connector B (36P) No. 25
   Terminal B	Body ground

   - 3. Turn the vehicle to the ON mode, and keep pressing the engine start/stop switch.

   - 4. Measure the voltage between test points 1 and 2.

   Test condition	Vehicle ON mode Keyless access/TPMS control unit connector B (36P): disconnected
   Test point 1	Keyless access/TPMS control unit connector B (36P) No. 10 - Refer to: Keyless Access/TPMS Control Unit Connector for Inputs and Outputs (2016 2017 2018) or Keyless Access/TPMS Control Unit Connector for Inputs and Outputs (2019 2020 2021) .
   Test point 2	Keyless access/TPMS control unit connector B (36P) No. 11 - Refer to: Keyless Access/TPMS Control Unit Connector for Inputs and Outputs (2016 2017 2018) or Keyless Access/TPMS Control Unit Connector for Inputs and Outputs (2019 2020 2021) .

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

   YES 

   Go to step 5.

   NO 

   Go to step 4.

4. Engine start/stop switch check

   -1. Turn the vehicle to the OFF (LOCK) mode.

   - 2. Test the engine start/stop switch. Test

   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 - Removal and Installation .

5. Engine start/stop switch VCONT line check

   -1. Turn the vehicle to the OFF (LOCK) mode.

   - 2. Reconnect the following connector.

   Keyless access/TPMS control unit connector B (36P)

   - 3. Disconnect the following connector.

   Engine start/stop switch 12P connector

   - 4. Turn the vehicle to the ON mode.

   - 5. Measure the voltage between test points 1 and 2.

   Test condition	Vehicle ON mode Engine start/stop switch 12P connector: disconnected
   Test point 1	Engine start/stop switch 12P connector No. 2
   Test point 2	Body ground

   Courtesy of HONDA, U.S.A., INC.

   Is there battery voltage?

   YES 

   Go to step 6.

   NO 

   Go to step 8.

6. Shorted wire check (DIN/DOUT, DCK lines)

   -1. Turn the vehicle to the OFF (LOCK) mode.

   - 2. Disconnect the following connector.

   Keyless access/TPMS control unit connector B (36P)

   - 3. Check for continuity between test points 1 and 2.

   Test condition	Vehicle OFF (LOCK) mode Keyless access/TPMS control unit connector B (36P): disconnected Engine start/stop switch 12P connector: disconnected
   Test point 1	Keyless access/TPMS control unit connector B (36P) No. 21 - Refer to: Keyless Access/TPMS Control Unit Connector for Inputs and Outputs (2016 2017 2018) or Keyless Access/TPMS Control Unit Connector for Inputs and Outputs (2019 2020 2021) .
   Test point 2	Body ground

   Test point 1	Keyless access/TPMS control unit connector B (36P) No. 20 - Refer to: Keyless Access/TPMS Control Unit Connector for Inputs and Outputs (2016 2017 2018) or Keyless Access/TPMS Control Unit Connector for Inputs and Outputs (2019 2020 2021) .
   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)

   -1. Connect terminals A and B with a jumper wire.

   Terminal A	Keyless access/TPMS control unit connector B (36P) No. 20 - Refer to: Keyless Access/TPMS Control Unit Connector for Inputs and Outputs (2016 2017 2018) or Keyless Access/TPMS Control Unit Connector for Inputs and Outputs (2019 2020 2021) .
   Terminal B	Keyless access/TPMS control unit connector B (36P) No. 21 - Refer to: Keyless Access/TPMS Control Unit Connector for Inputs and Outputs (2016 2017 2018) or Keyless Access/TPMS Control Unit Connector for Inputs and Outputs (2019 2020 2021) .

   - 2. Check for continuity between test points 1 and 2.

   Test condition	Vehicle OFF (LOCK) mode Keyless access/TPMS control unit connector B (36P): disconnected Engine start/stop switch 12P connector: disconnected
   Test circuit	DIN/DOUT, DCK
   Test point 1	Engine start/stop switch 12P connector No. 9
   Test point 2	Engine start/stop switch 12P connector No. 11

   Courtesy of HONDA, U.S.A., INC.

   Is there continuity?

   YES 

   The DIN/DOUT and DCK wires are OK. Replace the Keyless Access/TPMS Control Unit - Removal and Installation .

   NO 

   Repair an open or high resistance in the wire.

8. Shorted wire check (VCONT line)

   -1. Turn the vehicle to the OFF (LOCK) mode.

   - 2. Disconnect the following connector.

   Keyless access/TPMS control unit connector B (36P)

   - 3. Check for continuity between test points 1 and 2.

   Test condition	Vehicle OFF (LOCK) mode Keyless access/TPMS control unit connector B (36P): disconnected Engine start/stop switch 12P connector: disconnected
   Test point 1	Keyless access/TPMS control unit connector B (36P) No. 24 - Refer to: Keyless Access/TPMS Control Unit Connector for Inputs and Outputs (2016 2017 2018) or Keyless Access/TPMS Control Unit Connector for Inputs and Outputs (2019 2020 2021) .
   Test point 2	Body ground

   Is there continuity?

   YES 

   Repair a short to ground in the wire.

   NO 

   The VCONT wire is not shorted. Go to step 9.

9. Open wire check (VCONT line)

   -1. Connect terminals A and B with a jumper wire.

   Terminal A	Keyless access/TPMS control unit connector B (36P) No. 24 - Refer to: Keyless Access/TPMS Control Unit Connector for Inputs and Outputs (2016 2017 2018) or Keyless Access/TPMS Control Unit Connector for Inputs and Outputs (2019 2020 2021) .
   Terminal B	Body ground

   - 2. Check for continuity between test points 1 and 2.

   Test condition	Vehicle OFF (LOCK) mode Keyless access/TPMS control unit connector B (36P): disconnected Engine start/stop switch 12P connector: disconnected
   Test point 1	Engine start/stop switch 12P connector No. 2
   Test point 2	Body ground

   Courtesy of HONDA, U.S.A., INC.

   Is there continuity?

   YES 

   The VCONT wire is OK. Replace the Keyless Access/TPMS Control Unit - Removal and Installation .

   NO 

   Repair an open or high resistance in the wire.