Ignition Switch Illegal Input Code
Your car's ignition switch is sending a signal that doesn't match what the computer expects, like a key that's partially turned. The vehicle's body control module can't understand the ignition position and triggers this fault.
The body control module monitors voltage signals from the ignition switch across multiple positions (Off, Acc, Run, Start). It expects specific voltage levels and switch state sequences. When the signal falls outside normal parameters or transitions illegally, the fault code triggers.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Ignition Switch Voltage | Discrete levels: 0V (Off), ~5V (Acc), ~12V (Run), variable (Start) | Voltage outside expected range or invalid state transitions detected |
| Signal Transition Timing | Sequential state changes within 500ms per transition | Rapid or erratic switching, missing states, or stuck positions |
Code B1595 is a low-severity fault. Your vehicle is generally safe to drive to a workshop for diagnosis. However, do not ignore it indefinitely — low-severity codes often indicate developing problems that become expensive if neglected. Book a diagnostic appointment within 2–4 weeks. If you notice any additional symptoms (rough running, power loss, unusual smells), treat it as higher priority.
Once the fault is repaired, B1595 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.