What this code means
B1129 may indicate that the driver’s door lock knob switch input is being interpreted abnormally by the power window master switch.
What the vehicle may do
- Door lock operation may act inconsistent.
- The code may appear during body electrical or door lock diagnosis.
Possible fault areas
- Possible driver’s door lock knob switch signal circuit issue.
- Possible wiring or connector issue between the driver’s door latch and power window master switch.
- Possible power window master switch involvement after circuit checks are normal.
Diagnostic path
Opening context
On this 2016 through 2024 Honda Civic with the 1.5 turbo engine, B1129 points to a possible driver’s door lock knob switch malfunction. In plain terms, the power window master switch may be seeing the driver’s door lock and unlock switch signals at the same time, which it treats as an abnormal input. The driver may notice door lock operation that acts inconsistent, or the code may show up during body electrical diagnosis. The broad areas to keep in mind are the driver’s door lock knob switch signal circuits, the wiring between the latch and power window master switch, connector condition, and the power window master switch itself.
Start with the basic checks
Before getting into pinpoint testing, start with the basic system checks and follow a structured diagnostic approach. If other body network codes are present at the same time, handle that network diagnosis first so you are not chasing a symptom caused by a larger communication or input issue.
Confirm the fault
To confirm the complaint for B1129, operate the driver’s door lock knob switch on and off several times. The logic behind this code is simple: if the power window master switch detects the lock signal and the unlock signal at the same time, it stores the fault. So the goal is to reproduce the operating condition before separating the circuit for testing.
Set up the circuit test
Next, isolate the circuit. Disconnect the power window master switch 37P connector, then disconnect the driver’s door latch 10P connector. With those connectors separated, you can check the DR_SILCON_LOCK and DR_SILCON_UNLOCK circuits without the components influencing the reading.
Check for a wire-to-wire short
Now perform the shorted wire inspection between DR_SILCON_LOCK and DR_SILCON_UNLOCK. With IG Mode OFF, check for a shorted wire-to-wire condition between those two circuits. Normal is more than 1 MΩ. If the reading is abnormal, treat that as a circuit problem and stay with the wiring diagnosis.
Check each signal circuit to ground
After the wire-to-wire check, use the normal open and short inspection method and continue based on what you find. With IG Mode OFF, inspect DR_SILCON_LOCK for a short to ground. Normal is not shorted. Then inspect DR_SILCON_UNLOCK for a short to ground. Normal is also not shorted. If either circuit is abnormal, the problem is in that circuit, so pause, recheck the earlier diagnostic path, and avoid guessing.
When the circuits test normal
If the other inspection items all indicate normal, the remaining suspect in this diagnostic path is the power window master switch. At that point, the circuit checks have not shown the lock or unlock signal wiring shorted together or shorted to ground, so the fault is being narrowed to the master switch side of the system.
Verify the result
Keep verification separate from the circuit testing. After the fault path is corrected, verify the repair and confirm the code stays gone by operating the driver’s door lock knob switch again under the same type of conditions used to confirm the fault. The takeaway: for B1129, do not jump straight to a part. Prove whether the lock and unlock signal circuits are shorted together, shorted to ground, or testing normal before calling the master switch suspect. For more diagnostic training, visit stepdiagnostics.com.
Final check
B1129 is best approached as a signal circuit diagnosis: confirm the condition, isolate the connectors, check the lock and unlock circuits for shorts, and only then narrow the fault to the remaining in
For more guided automotive diagnostics, visit STEP Diagnostics.
