C1100 indicates that the ABS control module has detected an electrical malfunction in the circuit that switches power to the hydraulic pump motor—typically a fault in the pump relay, its wiring, or the motor itself. When this code is set, the ABS function is usually disabled to prevent unsafe braking behavior, though conventional hydraulic braking remains operational. The "switch" refers to the high-current relay or driver circuit that energizes the pump, not a mechanical switch inside the passenger compartment.
The relay that supplies high-current power to the pump motor is often integrated into the ABS hydraulic control unit and can fail due to contact arcing, coil burnout, or internal corrosion, causing an open or shorted switch circuit.
Corroded, chafed, or loose terminals in the power, ground, or control wiring between the ABS module and the pump motor can create high resistance or intermittent opens that trigger the failure code.
A seized, binding, or internally shorted pump motor can draw amperage beyond the relay rating or cause voltage collapse, leading the module to flag the switch circuit as failed.
High resistance or corrosion in the main ground path for the ABS modulator or pump motor can cause voltage drop errors that the module interprets as a switch circuit malfunction.
Rarely, the transistor or driver circuit inside the ABS module that operates the pump relay can fail; this should only be considered after verifying all external wiring, relay, and motor integrity.
Yes, but with caution. Standard base braking remains fully functional; however, the anti-lock function is disabled, so wheels can lock up during emergency stops on slippery surfaces. Repair should be prioritized.
No. C1100 is a chassis code for the ABS pump circuit, which is managed by the ABS control module, not the powertrain control module. Replacing the engine computer will not resolve this issue and is an incorrect repair.
Usually not. In most systems, the pump motor relay is integrated into the ABS hydraulic control unit assembly. While some specialist services rebuild these units, the standard service part is often the complete hydraulic modulator or a pigtail repair for wiring faults.
An immediate return indicates a hard fault—such as a broken wire, blown fuse, or failed relay—rather than an intermittent glitch. The circuit must be repaired before the code will stay clear.