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Home / DTC / C0566 — Brake Booster Solenoid Circuit/Open

C0566 — Brake Booster Solenoid Circuit/Open

Detailed page for trouble code C0566.

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Code

C0566

Generic C — Chassis

Brake Booster Solenoid Circuit/Open

Brand: Generic
Type: C — Chassis
Views: UK: 15 EN: 27 RU: 22
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Page language: EN

Causes

  • Open or broken wiring in the solenoid circuit
  • Disconnected or corroded connector at solenoid or control module
  • Failed (open) brake booster solenoid coil
  • Blown fuse or faulty relay supplying the circuit
  • Poor or missing ground
  • Faulty ABS/brake control module

Symptoms

  • Brake warning lamp and/or ABS warning light illuminated
  • Increased brake pedal effort or reduced brake assist
  • Possible change in idle or engine running when braking (if vacuum/assist affected)
  • Diagnostic trouble code stored and faults present in ABS/brake module
  • Intermittent loss of brake assist if connection is intermittent

What to check

  • Retrieve freeze frame and related codes with a scan tool; note conditions when C0566 set
  • Visual inspection of wiring and connectors between booster solenoid and control module
  • Check fuses and relays that feed the solenoid circuit
  • Measure continuity and resistance of solenoid supply and ground circuits
  • Backprobe connector to verify presence of supply voltage and ground when commanded
  • Command solenoid from scan tool (if supported) and observe response

Signal parameters

  • Supply voltage: typically battery voltage (near 12 V) when circuit is powered; varies by design
  • Control signal: either switched 12 V or ground, sometimes PWM; refer to vehicle-specific wiring diagram
  • Solenoid coil resistance: typically low ohms (example range 5–50 Ω depending on design) — check service manual for exact value
  • Open-circuit condition: infinite/very high resistance or no voltage present at solenoid connector when expected

Diagnostic algorithm

  1. Confirm code and any related DTCs with a scan tool. Note whether code is current or historic.
  2. Visually inspect connectors and harness to the brake booster solenoid and ABS/brake module for damage, corrosion, or disconnection.
  3. Check related fuses and relays. Replace any blown fuses and test relays for proper operation.
  4. With ignition ON, backprobe the solenoid connector. Verify supply voltage and ground presence. If no voltage or ground, trace back toward the fuse/relay and module.
  5. Measure solenoid coil resistance with the connector disconnected. Compare to service manual specification. An open (infinite) reading indicates a failed solenoid.
  6. Check continuity between the solenoid connector and the control module pins. Repair any open circuits, broken wires, or bad grounds found.
  7. If wiring and solenoid are good, command the solenoid with a scan tool (or apply proper test voltage briefly) to verify operation. Observe voltage and current behavior while commanded.
  8. If wiring and solenoid test good but code persists, inspect the ABS/brake control module outputs and grounds. Consider module replacement or repair only after confirming external circuit integrity.
  9. After repairs, clear codes, perform functional tests and a road test to confirm the fault does not return.

Likely causes

  • Damaged harness or chafed wire near steering column or engine bay causing an open
  • Connector pins corroded or pushed out at the solenoid or module
  • Solenoid coil internally open (electrical failure)
  • Fuse for solenoid circuit blown or relay contacts failed
  • Ground strap or ground terminal loose/corroded near booster

Fault status

⚠️ Status
Brake Booster Solenoid Circuit/Open — electrical open or high resistance in solenoid circuit detected. Check wiring, connectors, fuse/relay, solenoid coil, and control module.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

C0565 C0567 C0570 C0555
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