What this code means
B1140 may indicate that the driver's power window master switch is detecting a mismatch between the learned or recognized window position and the actual driver's window position.
What the vehicle may do
- The driver's power window may operate with position-learning or initialization issues.
- The vehicle may store the code when the switch-recognized window position does not match the actual window position.
- Related power-window or multiplex-control faults may affect the diagnostic direction.
Possible fault areas
- Power window master switch position-detection logic
- Driver's power window position recognition
- Related power-window or multiplex-control fault areas
Diagnostic path
Opening context
On this Civic, B1140 points to a driver's power window position detect circuit malfunction. In plain terms, the power window master switch may be seeing the driver's window in one position while the actual glass position is different. When that mismatch is detected, the switch can store the code. The driver window may operate normally, may lose learned position behavior, or may need initialization-type service. Broadly, the possible fault area is the driver's power window master switch and its position-detection logic, with related power-window or multiplex-control faults handled first if they are present.
Start with the basic path
Before getting deep into B1140, start with the basic troubleshooting checks for this system. If the vehicle has multiple stored codes, do not jump straight into this one. Follow the multiple-code diagnostic path first, and if there are related power-window or multiplex-control faults stored, diagnose those first. That matters here because B1140 depends on the master switch knowing where the driver's window actually is.
Main B1140 check
For the B1140 path itself, the inspection item is the power window master switch, and the work item is resetting the power window master switch. Turn the vehicle to the ON mode. Then use the power window master switch to manually open and close the driver's power window. The diagnostic idea is simple: the switch is being checked against the actual movement and position of the driver's window after the reset process.
Verification and takeaway
Keep the verification separate from the reset action. After the reset and manual window operation, confirm the original complaint and code status according to the normal scan-tool workflow for the vehicle. If the path does not clearly move forward from there, pause, recheck the earlier diagnostic path, and avoid guessing. Takeaway: for B1140, handle other stored faults first, reset the power window master switch, then manually run the driver's window and verify the code stays gone. For more diagnostic training, visit stepdiagnostics.com.
Final check
B1140 is approached by handling other related stored faults first, then resetting the power window master switch and manually operating the driver's window before verification.
For more guided automotive diagnostics, visit STEP Diagnostics.
