ANTI THEFT INPUT SIGNAL SHORT TO GROUND
Your car's anti-theft system is detecting a broken wire or loose connection that's touching ground, like a severed phone line shorting out. The security module can't properly read the signal, so it flags this fault.
The ECU monitors the anti-theft input signal voltage, expecting a specific range when the system is armed or disarmed. A short to ground pulls the signal voltage to 0V, which the module detects as an abnormal condition outside safe operating parameters.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Anti-Theft Input Signal Voltage | 5V or specified operating range | 0V or below minimum threshold (short to ground) |
| Signal Resistance | Above 10 kΩ to ground | Below 1 kΩ (indicates short path) |
Code B2478 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, B2478 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.