C2551

Code

Generic C — Chassis

Brake hydraulic pump motor circuit malfunction

Brand: Generic

Type: C — Chassis

Views: UK: 4 EN: 6 RU: 5

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Page language: EN

Causes

Blown fuse or tripped relay in pump motor supply
Open, shorted or corroded wiring or connector to the pump motor
Faulty pump motor (internal short, open winding, high resistance)
Faulty ABS/BAS/ESP control module or driver output transistor
Poor ground connection at the pump motor or module
Water ingress, contamination or mechanical seizure of the pump

Symptoms

ABS, traction control or brake warning lamp illuminated
Reduced or lost ABS functionality, loss of hill-hold or stability assist
Unusual pump noise (noisy, grinding) or no pump noise when activated
Longer-than-normal brake pedal build or unexpected pedal feel
Recurring or intermittent warning lamp

What to check

Retrieve freeze-frame and stored codes with a capable scan tool; note related codes
Visual inspection of pump, wiring harness, connectors and fuse/relay(s)
Check battery voltage and general charging system health
Measure supply voltage at pump connector with ignition on / during activation
Verify ground continuity from pump motor ground to chassis/negative battery
Measure motor winding resistance (compare to spec) and check for shorts to ground

Signal parameters

Battery supply voltage at pump: ~11.5–14.5 V (ignition on/run)
Motor winding resistance (typical): commonly 1–20 ohm depending on design — refer to OEM spec
Crank-in/activation current draw: can range from a few amps to 20–40 A peak (consult OEM)
Control module output: PWM or switched 0–12 V (duty cycle varies with command)
PWM frequency (if used): commonly 50–500 Hz (refer to vehicle spec)
Ground continuity: near 0 ohm between pump ground and chassis

Diagnostic algorithm

Safety: Park on level, chock wheels, disable ignition and disconnect battery if performing repairs on wiring. Follow vehicle-specific safety procedures.
Connect scan tool: Read and record C2551 and any related codes; note freeze-frame and live data during an ABS pump request.
Visual inspection: Check fuses, relays, pump connector(s) for corrosion, bent pins, moisture, or damage. Inspect harness for abrasion or heat damage.
Power check: With ignition on, measure battery voltage at the pump power pin. If missing, trace back to fuse/relay and repair as needed.
Ground check: Measure resistance between pump ground pin and battery negative; repair high resistance or open ground.
Motor winding test: Disconnect pump, measure DC resistance across motor terminals; compare to spec. High/open indicates motor or connector fault; low/short to ground indicates internal fault.
Control signal test: Reconnect harness, backprobe control line and use oscilloscope or lab scope to observe PWM/drive signal while commanding pump via scan tool. No signal — suspect module/relay; abnormal waveform — suspect wiring or module output.
Current draw test: With safe clamp meter/probe, measure motor current while pump runs. Excessive current may indicate mechanical seizure; no current indicates open circuit or driver fault.
Wiggle / load test: Wiggle harness and connectors while monitoring voltage/signal to reproduce intermittent faults.
Isolate faults: If wiring and power/ground are good but pump motor failure confirmed, bench-test or replace pump assembly. If pump good but no proper control signal, continue module and wiring diagnosis per OEM procedures.
Repair and retest: Repair or replace failed components, clear codes, perform system relearn (if required), and verify proper operation and no return of C2551.

Likely causes

Corroded or loose connector at the pump motor
Failed pump motor winding or brushes
Blown fuse or bad pump relay
Open or short in supply/ground wiring
Control module output driver fault

Fault status

⚠️ Status

Brake hydraulic pump motor circuit malfunction detected — control module has identified abnormal electrical condition (open/short/high resistance/intermittent) in pump motor circuit. Brake/ABS warning lamp may be illuminated.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-2.5 hours