C1100 — ABS Pump Switch Circuit Failure - Generic

Causes

• Blown fuse or tripped circuit breaker supplying ABS pump/switch
• Open or shorted wiring in the pump switch circuit (including chafing, pinched harness)
• Corroded, loose, or damaged connector at the ABS pump/switch
• Failed ABS pump switch (pressure switch) or internal switch contacts
• Faulty ABS pump motor or relay causing abnormal circuit conditions
• Faulty ABS hydraulic control module or internal driver

Symptoms

• ABS warning lamp illuminated; sometimes traction/ESP light as well
• ABS pump may run continuously, run abnormally, or not run at all
• Brake pedal pulsation or reduced ABS function during braking
• ABS/traction control disabled; possible illuminated stability control lamp
• Stored C1100 (may be accompanied by other ABS-related codes)
• Unusual noise from ABS pump (clicking or motor noise)

What to check

• Read and record all ABS-related codes and freeze-frame data with a scan tool; note any accompanying codes
• Visually inspect ABS pump, pressure/switch connector, and wiring harness for damage, corrosion, or water intrusion
• Check fuses and relays related to ABS pump power and replace if blown/faulty
• Backprobe connector pins with key ON and while commanding pump via scan tool to verify supply and ground
• Measure voltage at pump power terminal (key ON and cranking) and check for voltage drop under load
• Perform continuity and resistance checks on switch circuit to ground and to the ABS module

Signal parameters

• Battery supply to pump/pump switch: approx. battery voltage (~11–14 V with key ON/engine running)
• Control/switch output when activated: typically near 0 V (ground) if driven low, or close to battery voltage if driven high depending on design — verify with vehicle-specific wiring diagram
• Pump motor coil resistance (typical range varies by vehicle): commonly low ohms (examples 0.2–5 Ω) — consult service data for exact value
• Switch continuity: closed (low ohms) when switch reports "active"; open/infinite when "inactive" — confirm expected state with applied pressure or commanded actuator
• Normal ABS pump current during operation: moderate steady draw; excessive current (> specification) indicates mechanical bind or shorted windings (use vehicle-specific values)

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