C0594

Code

Generic C — Chassis

Brake Booster Motor A Performance

Brand: Generic

Type: C — Chassis

Views: UK: 24 EN: 27 RU: 14

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Page language: EN

Causes

Open, short or high-resistance wiring/connectors to brake booster motor
Faulty brake booster motor or internal gearbox
Weak battery or charging system (low supply voltage)
Poor or corroded ground
Blown fuse or failed relay for the booster motor
Mechanical binding or seized booster components

Symptoms

Increased brake pedal effort or longer pedal travel
Reduced or inconsistent brake assist
Brake warning light and/or ABS light illuminated
Stored fault code C0594 (and possibly related codes)
Possible unusual motor noise from booster area
Intermittent or degraded regenerative braking behavior on some vehicles

What to check

Read DTCs and freeze-frame data with a capable scanner; note related codes
Verify battery state-of-charge and charging system voltage (engine running ~13.5–14.5 V)
Visual inspection of motor, connector, wiring harness and ground points for damage or corrosion
Check fuses and relays for booster motor power
Backprobe motor connector while commanding motor with scan tool; observe voltage and waveform
Measure motor supply voltage and ground continuity with connector disconnected

Signal parameters

Supply voltage to motor: nominally 11–14.5 V when system healthy
Control input: PWM or switched drive from brake/ABS module (0–12 V range dependent on design)
Motor current draw: typically low at idle; expect nominal operating current under full load to be within manufacturer spec (peaks can be significantly higher) — unusually high current indicates binding or shorted windings
Connector pin resistance: low ohms between motor power and ground when motor not energized; open/high resistance indicates wiring/connector issue
Diagnostic commands should produce consistent command voltage and corresponding motor current

Diagnostic algorithm

Capture DTCs, freeze-frame and live data. Note any related ABS/brake codes and events that coincide with the fault.
Verify battery and charging system health. Recharge or replace weak battery before further testing.
Perform thorough visual inspection of booster motor, harness, pins and grounds. Repair any damaged wiring or corrosion.
Check fuses and relays for the booster motor circuit; replace as needed.
With a scan tool, command the booster motor/actuator while monitoring supply voltage, control signal (PWM) and motor current. Look for expected responses.
Backprobe the motor connector with harness connected to measure voltage at the motor during commanded operation. Confirm stable supply and proper control signal.
Disconnect motor and measure DC resistance across motor terminals. Compare to service values if available; an open or very low resistance indicates a fault.
If wiring and inputs are good but motor fails to operate or draws abnormal current, remove and bench-test or replace the motor/booster assembly.
If motor bench test shows good operation, suspect module/motor driver fault. Inspect module grounds and power; consider module replacement only after wiring and actuator are proven good.
After repair, clear codes and perform calibration/actuator relearn if required. Road test and re-scan to confirm repair.

Likely causes

Damaged motor power lead or connector causing intermittent voltage
Motor windings or internal bearings failed causing abnormal current draw
Low system voltage during motor operation (battery/alternator issue)
Faulty motor driver inside ABS/brake control module
Contaminated/corroded ground at booster motor

Fault status

⚠️ Status

Brake Booster Motor A Performance — the brake control module detected abnormal operation of the electric brake booster motor (motor A). Possible causes include wiring/connector faults, low system voltage, a failing motor, mechanical binding or module driver failure.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5 - 3.0 hours

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