Brake Pressure Switch Mechanical Failure
The brake pressure switch has stopped working properly, so your vehicle can't detect when you're pressing the brake pedal. It's like a light switch that's physically broken and won't click on or off anymore.
The ECU monitors voltage signals from the brake pressure switch, which toggles between closed and open circuits as brake pressure changes. The switch should activate at a specific pressure threshold (typically 3-5 bar) when brakes are applied. A mechanical failure prevents proper signal transmission to the ABS module.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Brake Pressure Switch Signal | 0V (off) / 5V (on) with brake application | No signal change or stuck at one state |
| Pressure Activation Point | 3-5 bar brake pressure | Switch unresponsive at normal pressure range |
Code C1940 is classified as a serious fault. If your check engine light is flashing — not just steady — pull over safely and do not continue driving. A flashing CEL indicates an active misfire or critical failure that can cause catalytic converter damage within minutes or permanent engine harm within miles. Contact a certified mechanic immediately. Do not attempt roadside repairs on high-severity codes unless you are trained to do so.
Once the fault is repaired, C1940 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.