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. Turn the vehicle to the ON mode.

   - 2. Clear the DTCs with the HDS.

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

   - 4. 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.

   - 5. 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 5 times.

   - 6. Check for DTCs with the HDS.

   DTC Description	DTC
   B1931 Backup control unit no response

   Is DTC B1931 indicated?

   YES 

   Go to step 2 below.

   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 10P connector .

   Is the connections OK?

   YES 

   Go to step 3 below.

   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:

   - 1. Disconnect the following connector.

   Keyless access control unit connector B (36P)

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

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

   Test condition	Vehicle ON mode Keyless access control unit connector B (36P): disconnected
   Test point 1	Keyless access control unit connector B (36P) No. 10
   Test point 2	Keyless access control unit connector B (36P) No. 11

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

   YES 

   Go to step 5 below.

   NO 

   Go to step 4 below.

4. Engine start/stop switch check:

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

   - 2. Test the engine start/stop switch .

   Is the engine start/stop switch OK?

   YES 

   Repair an open or high resistance in the SS1 (+) and/or SS2 (-) wire(s).

   NO 

   The SS1 (+) and SS2 (-) wires are OK. Replace the engine start/stop switch .

5. Engine start/stop switch SS SW VCONT line check:

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

   - 2. Reconnect the following connector.

   Keyless access control unit connector B (36P)

   - 3. Turn the vehicle to the ON mode.

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

   Test condition	Vehicle ON mode
   Test point 1	Engine start/stop switch 10P connector No. 7
   Test point 2	Body ground

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

   Is there battery voltage?

   YES 

   Go to step 6 below.

   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 connectors.

   Keyless access control unit connector B (36P)

   Engine start/stop switch 10P connector

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

   Test condition	Vehicle OFF (LOCK) mode
   	Keyless access control unit connector B (36P): disconnected
   	Engine start/stop switch 10P connector: disconnected
   Test point 1	Keyless access control unit connector B (36P) No. 21
   Test point 2	Body ground

   Test point 1	Keyless access control unit connector B (36P) No. 20
   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 below.

7. Open wire check (DIN/DOUT, DCK lines):

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

   Test condition	Vehicle OFF (LOCK) mode
   	Keyless access control unit connector B (36P): disconnected
   	Engine start/stop switch 10P connector: disconnected
   Test point 1	Keyless access control unit connector B (36P) No. 21
   Test point 2	Engine start/stop switch 10P connector No. 9

   Test point 1	Keyless access control unit connector B (36P) No. 20
   Test point 2	Engine start/stop switch 10P connector No. 10

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

   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):

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

   - 2. Disconnect the following connectors.

   Keyless access control unit connector B (36P)

   Engine start/stop switch 10P connector

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

   Test condition	Vehicle OFF (LOCK) mode
   	Keyless access control unit connector B (36P): disconnected
   Test point 1	Keyless access control unit connector B (36P) No. 24

   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 below.

9. Open wire check (SS SW VCONT line):

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

   Test condition	Vehicle OFF (LOCK) mode
   	Keyless access control unit connector B (36P): disconnected
   	Engine start/stop switch 10P connector: disconnected
   Test point 1	Keyless access control unit connector B (36P) No. 24
   Test point 2	Engine start/stop switch 10P connector No. 7

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

   Is there continuity?

   YES 

   Replace the keyless access control unit .

   NO 

   Repair an open or high resistance in the wire.

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