ABS Pump Switch Circuit Failure
The ABS pump motor isn't responding to electrical commands from the brake control module, like a light switch that won't turn the lamp on. This prevents the ABS system from building pressure to prevent wheel lockup during hard braking.
The ABS module sends a control signal to the pump motor relay and monitors the pump's feedback voltage or current draw to confirm operation. It expects to see a change in voltage or resistance when the pump activates during ABS events.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Pump Motor Control Signal | 5V switching signal present, motor draws 3-8A when active | No signal response or open/short circuit detected; 0V or excessive resistance |
| Pump Feedback Voltage | 12V nominal when pump runs; drops during pressure buildup | Stuck at 0V or 12V; no change in voltage state |
Code C1100 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, C1100 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.