DTC B1127: Driver's Door Key Cylinder Switch Input Circuit Malfunction (Simultaneous Input Of Lock and Unlock Signal)

NOTE: If you are troubleshooting multiple DTC's, be sure to follow the instruction B-CAN System Diagnosis Test Mode A. (see TROUBLESHOOTING - B-CAN SYSTEM DIAGNOSIS TEST MODE A )

NOTE: You will need two keys to do this troubleshooting.

Clear the DTCs with the HDS.
Turn the ignition switch to LOCK (0) and then back to ON (II).
Insert the ignition key into the driver's door key cylinder switch, and turn the key to the LOCK and UNLOCK positions 10 times.
Check for DTCs with the HDS.
Is DTC B1127 indicated?

YES - Go to step 5.

NO - Intermittent failure, the driver's door key cylinder switch system is OK at this time. Check for loose or poor connections.
With the driver's door key cylinder in the neutral position, select KEYLESS with the HDS, and enter the DATA LIST.
Check the ON/OFF information of the DRIVER'S DOOR KEY CYLINDER SWITCH (LOCK) and DRIVER'S DOOR KEY CYLINDER SWITCH (UNLOCK) in the DATA LIST.
Are both information indicators OFF?

YES - Faulty MICU, replace the under-dash fuse/relay box:
- For USA model (see USA MODELS ).
- For Canada model (see CANADA MODELS ).
NO - Go to step 7.
Disconnect the driver's door lock actuator 10P connector.
Check the ON/OFF information of the DRIVER'S DOOR KEY CYLINDER SWITCH (LOCK) and DRIVER'S DOOR KEY CYLINDER SWITCH (UNLOCK) in the DATA LIST.
Are both information indicators OFF?

YES - Faulty driver's door key cylinder switch; replace the driver's door lock actuator.

NO - Go to step 9.
Turn the ignition switch to LOCK (0).
Disconnect under-dash fuse/relay box connector E (12P).
Check for continuity between under-dash fuse/relay box connector E (12P) terminals No. 4 (UNLOCK) and No. 3 (LOCK) and body ground individually.
Is there continuity?

YES - Repair short to ground in the LOCK or UNLOCK wire.

NO - Go to step 15.

Fig 1: Checking Continuity Between Under-Dash Fuse/Relay Box Connector E (12P) Terminals No. 4, No. 3 & Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Turn the ignition switch to LOCK (0).
Disconnect the driver's door lock actuator 10P connector.
Disconnect under-dash fuse/relay box connector E (12P).
Check for continuity between under-dash fuse/relay box connector E (12P) terminals No. 4 (UNLOCK) and No. 3 (LOCK).
Is there continuity?

YES - Repair short in the wire between the LOCK and UNLOCK wires.

NO - Faulty MICU, replace the under-dash fuse/relay box:
- For USA model (see USA MODELS ).
- For Canada model (see CANADA MODELS ).
Fig 2: Checking Continuity Between Under-Dash Fuse/Relay Box Connector E (12P) Terminals No. 4 & No. 3
Courtesy of AMERICAN HONDA MOTOR CO., INC.