C0593

Code

Generic C — Chassis

Brake Booster Motor B Phase U-V-W Current Low

Brand: Generic

Type: C — Chassis

Views: UK: 19 EN: 19 RU: 14

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Page language: EN

Causes

Open or high-resistance wiring in the B-phase motor circuit (broken conductor, corroded connector)
Short/open in motor winding for the B phase
Loose, corroded or damaged motor connector pins
Blown fuse or faulty relay supplying the motor / motor controller
Faulty motor driver (inverter) or MOSFET/IGBT for B phase
Faulty current sensor or sensing circuit for the B phase

Symptoms

Brake assist reduced or unavailable; increased brake pedal effort
Brake warning lamp and/or ABS/ESP indicator illuminated
Stored fault code(s) C0593 (and possibly related motor phase codes)
Possible limp or reduced-function braking mode
Unusual motor noise or no motor movement when boost requested
Intermittent or permanent loss of electric boost depending on severity

What to check

Read and record freeze-frame and live data with a scan tool; note battery voltage and motor demand when code sets
Check for other related codes (other phase codes, current sensor, supply voltage, module faults)
Visual inspection of motor harness, connector seals, pin condition and for damage/corrosion
Check fuses and relays for motor and motor controller circuits
Measure supply voltage to motor controller and at motor connector while commanding boost
Measure resistance of motor windings (U-V-W) for continuity and similarity

Signal parameters

Expected: Similar current magnitude in all three motor phases (U, V, W) when motor is driven; values vary by design and load—check manufacturer specs
Actual: B-phase current significantly lower or near 0 A while other phases show normal current
Supply voltage to motor controller should be within battery/system spec during test
PWM frequency/duty cycle from controller should be present on all three phase outputs when motor commanded
Motor winding resistances (U-V, V-W, U-W) should be near-equal and within spec

Diagnostic algorithm

Connect a scan tool and confirm C0593 is present. Note freeze frame: battery voltage, vehicle speed, brake demand, motor duty.
Check battery state and charging system; ensure adequate supply voltage before current tests.
Visually inspect motor harness, connectors and ground points for corrosion, damage, or loose pins. Repair as needed.
Check related fuses/relays. Replace if faulty and clear codes, then attempt to reproduce the fault.
With vehicle secure, command the brake booster motor (if supported by scan tool) and monitor phase currents and controller outputs live.
Back-probe motor controller outputs (U, V, W) and measure current using an AC/DC clamp meter or current probe; compare B-phase to A/C phases.
With motor disconnected, measure winding resistances between U-V, V-W, U-W for continuity and matching values. A reading of open or very high resistance indicates winding or connector fault.
Inspect/replace any damaged wiring or connectors. Repair grounds and power feeds as required.
If wiring and motor windings are good but B-phase current remains low, suspect the motor controller driver stage or current sensing circuit. Test/replace the motor controller or perform bench diagnostics according to manufacturer procedures.
After repairs, clear codes and road-test to confirm the fault does not return and that brake assist performance is restored.

Likely causes

Intermittent or high-resistance connector at the motor harness
Open winding or broken wire to B-phase winding
Failed driver transistor for B-phase in the motor controller
Contamination/corrosion at motor connector causing poor current flow
Damaged ground or supply causing low effective voltage to B-phase

Fault status

⚠️ Status

Stored fault indicates low current detected in Brake Booster Motor B phase (U/V/W). Possible causes include open or high-resistance wiring, bad connector, faulty motor winding, failed motor driver or current sensor, or low supply voltage. Inspect supply, wiring, motor and controller.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1-3 hours

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