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Home / DTC / B299D — Main cylinder open:close cycle

B299D — Main cylinder open:close cycle

Detailed page for trouble code B299D.

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Code

B299D

MITSUBISHI B — Body

Main cylinder open:close cycle

Brand: MITSUBISHI
Type: B — Body
AI status
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Completed 100%
Page language: EN

Causes

  • Electrical fault to actuator/valve (open/short/intermittent wiring, corroded connector)
  • Faulty solenoid valve or actuator in the main cylinder assembly
  • Faulty pump or motor that supplies hydraulic pressure
  • Low or contaminated brake fluid, air in hydraulic circuit
  • Mechanical internal failure in the master/main cylinder (seized valve, internal leakage)
  • ECU or hydraulic control module software/firmware fault or processor error

Symptoms

  • ABS / brake / traction control warning lamp illuminated
  • Brake pedal feels spongy, soft, or has inconsistent travel
  • Reduced or altered ABS/brake modulation during braking
  • Unusual pump motor noise (constant running or no running when commanded)
  • Diagnostic scanner shows failed or erratic actuator commands
  • Possible vehicle stability/traction intervention or degraded braking performance

What to check

  • Connect a diagnostic scanner and read B299D plus any other pending/related codes and freeze-frame data
  • Confirm vehicle battery voltage at rest and during actuator command (should stay within manufacturer spec)
  • Visually inspect wiring and connectors to the main cylinder/ABS hydraulic unit for damage, corrosion, or loose pins
  • Check brake fluid level and fluid condition; inspect for external leaks
  • Using the scan tool, command the main cylinder solenoid/pump and observe live data/actuator status and cycle counts
  • Measure solenoid coil resistance and compare to specification (refer to service manual)

Signal parameters

  • Command input to main cylinder solenoid: voltage 0–12 V (ON/OFF or PWM duty)
  • Solenoid duty cycle: 0–100% (manufacturer-specific active modulation)
  • Solenoid coil resistance: typically tens of ohms (check service spec)
  • Pump motor supply voltage: battery voltage during command (approx. 11–14 V)
  • Pump motor current draw: nominal running current per spec; very high or zero current indicates fault
  • Open/close cycle count: integer pulses per command (should match commanded cycles)

Diagnostic algorithm

  1. Record all active and historical codes and freeze-frame data with scan tool; note operating conditions when DTC set
  2. Attempt to reproduce fault by repeating diagnostic cycle while monitoring live data and actuation status
  3. Visually inspect hydraulic unit wiring, connectors, and harness for damage or corrosion; repair any issues and clear code to retest
  4. Check and top up brake fluid if low; bleed system if air is suspected and retest for code reset
  5. Using a scan tool, command the main cylinder solenoid(s) and pump while observing voltage, current, and status feedback; verify the unit responds to commands
  6. Measure solenoid coil resistance with multimeter; if out of specification, replace solenoid/valve assembly
  7. Measure pump motor supply voltage and current during commanded operation; if pump does not run or current is abnormal, test or replace pump/motor
  8. If electrical checks are good but the hydraulic response is incorrect, inspect internal master/main cylinder for mechanical failure and replace assembly if necessary
  9. If suspect ECU/hydraulic control module error after verifying harness and unit, check module power/ground and communications; consider reflashing software or replacing control module per manufacturer guidance
  10. After repairs, clear codes and perform road test/operational test to confirm the open/close cycle fault does not return

Likely causes

  • Intermittent wiring or connector fault to the main cylinder solenoid
  • Stuck or electrically failed open/close solenoid inside the main cylinder
  • Pump motor failure preventing correct pressure build/relief cycle
  • Low brake fluid level or air in lines causing abnormal cycle detection

Fault status

⚠️ Status
Main cylinder open/close cycle abnormal — hydraulic actuator (solenoid/pump) did not complete expected cycle
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

C1201 C0035 U0121 P0606 P0299
406

Browse 406 MITSUBISHI manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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