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Home / DTC / B1055 — Rear air mix damper motor

B1055 — Rear air mix damper motor

Detailed page for trouble code B1055.

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Code

B1055

MITSUBISHI B — Body

Rear air mix damper motor

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

Causes

  • Open or shorted wiring in the rear air mix damper motor circuit
  • Corroded or loose connector at the actuator
  • Failed rear air mix damper motor (electrical or mechanical)
  • Damper gear stripped or mechanical binding in duct or linkage
  • Faulty HVAC control module or incorrect actuator calibration/software

Symptoms

  • Rear cabin temperature not responding to controls (stuck hot or cold)
  • Rear air distribution works but temperature does not change
  • Unusual noise from rear HVAC area (grinding or clicking)
  • HVAC displays fault codes or rear climate functions inoperative

What to check

  • Visually inspect actuator and wiring harness for damage, corrosion, or disconnection
  • Check fuses related to HVAC/rear blower and accessory power
  • Operate rear temperature controls and listen for actuator movement
  • Use scan tool to read freeze frame data and live actuator status/position
  • Check for diagnostic trouble codes in HVAC/control module (additional codes may relate)

Signal parameters

  • Supply voltage to actuator: ~11–14 V (battery voltage) when the motor is commanded on (depends on vehicle and mode)
  • Ground: continuity to chassis ground (near 0 Ω) when checked at connector
  • Actuator resistance: typical DC motor/actuator coil resistance usually low (single-digit to tens of ohms) — expect roughly 5–50 Ω depending on actuator type (consult vehicle spec)
  • Position sensor/feedback voltage: often 0.5–4.5 V across travel (varies by design); should change smoothly as actuator moves
  • Current draw: actuator stall or excessive draw may exceed expected (often

Diagnostic algorithm

  1. Read and record all HVAC-related fault codes and freeze frame data with a scan tool.
  2. Perform a visual inspection: connectors, wiring harness, actuator mounting, and ducts for obstructions or broken gears.
  3. With ignition on, command the rear air mix actuator using a scan tool actuator test (or cycle rear temperature) and observe movement and feedback values.
  4. Measure supply voltage and ground at the actuator connector while commanding movement. Voltage should be near battery voltage; ground should be good.
  5. If there is power and ground but no movement, measure motor coil resistance for open/short. Compare to service data or look for abrupt open circuit.
  6. Probe the feedback/position signal while commanding movement. The voltage should change progressively; a fixed or erratic value indicates sensor or internal actuator failure.
  7. If electrical checks look OK but actuator does not move, remove actuator and attempt to move damper manually to check for mechanical binding or damaged gears/linkage.
  8. Direct bench test the actuator (apply proper battery voltage briefly, observing movement and current). Do not apply prolonged power to avoid damage.
  9. If actuator works off-vehicle, re-check harness continuity and connector while mounted; repair or replace wiring as needed.
  10. Clear codes, re-run actuator tests and road/test verify rear temperature control operation. If intermittent or unexplained failures persist, consider HVAC control module diagnosis or software/calibration update.

Likely causes

  • Connector corrosion or loose terminal at rear actuator
  • Motor armature or internal gears seized/worn
  • Broken or stripped actuator gear or linkage causing stall
  • Open/short in power, ground, or feedback signal wire

Fault status

⚠️ Status
Rear air mix damper motor circuit malfunction — actuator not responding or feedback out of range.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-1.5 hours

Similar codes

B1056 B1057 B1065 B1045 B1001
406

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