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Home / DTC / B28F4 — Window relay output:open line

B28F4 — Window relay output:open line

Detailed page for trouble code B28F4.

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Code

B28F4

MITSUBISHI B — Body

Window relay output:open line

Brand: MITSUBISHI
Type: B — Body
Views: UK: 19 EN: 26 RU: 26
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or broken wire between the body control module (BCM) / window ECU and the window relay
  • Corroded, loose or damaged relay connector or pin(s)
  • Failed window relay (coil or contacts open)
  • Blown fuse or fusible link feeding the relay or module
  • Poor ground for the relay or a related ground point
  • Faulty BCM / window control module output transistor or connector

Symptoms

  • One or more power windows will not operate
  • No clicking sound from the window relay when switch is operated
  • Windows stuck in one position or operate intermittently
  • No voltage present at window motor/relay output when commanded

What to check

  • Scan the vehicle and confirm B28F4 is stored; note freeze frame/occurrence conditions
  • Visually inspect window relay, fuse(s) and relay connector for corrosion, water ingress or damage
  • Verify fuse(s) related to power windows are intact
  • Check for relay operation (listen for click) while operating the window switch
  • Measure battery voltage at relay power terminal with key ON
  • Measure voltage at the relay output and at the window motor while commanding the window

Signal parameters

  • Battery voltage at relay power feed: ~12 V (key ON or when circuit powered)
  • Relay control output (command from module): switches between approx. 0 V (ground) and battery voltage or open when not commanded (use scan tool/oscilloscope if available)
  • Relay coil resistance (typical for standard automotive relays): roughly 50–200 ohms (varies by relay) — an open coil reads infinite resistance
  • Continuity check: expected low resistance between module output pin and relay control pin; an open line shows infinite/OL

Diagnostic algorithm

  1. Confirm the fault: read and record the code and any related codes. Clear codes and attempt to reproduce the fault to verify.
  2. Visual inspection: inspect relay, socket, related fuses, wiring harnesses and connectors for damage, corrosion or signs of water ingress. Repair obvious issues.
  3. Verify power and ground: with key ON, verify battery voltage at the relay power terminal and continuity of the relay ground to chassis.
  4. Relay bench test: remove relay and bench-test by applying 12 V to the coil terminals to confirm it clicks and the contacts close. If relay is open internally, replace it.
  5. Signal verification: command the window switch (or use a diagnostic actuator) while measuring at the relay control terminal. If the control module should drive the relay, you should see the expected switching signal (voltage change or ground switching).
  6. Wiring continuity: with ignition OFF and battery disconnected, perform continuity checks between the control module output pin and the relay control terminal. Repair any open circuits or broken wires.
  7. If wiring and relay are good but no drive signal from the module: inspect the module connector for bent pins and check for power/grounds to the module. Consider swapping or testing the module as per manufacturer procedure.
  8. After repair, clear codes and verify proper operation of windows and that the code does not return.

Likely causes

  • Broken/disconnected harness near door or relay mounting
  • Relay coil/contacts internally open
  • Corroded relay connector causing intermittent open
  • Open fuse or fusible link in the power feed
  • Output driver in the control module has failed

Fault status

⚠️ Status
Window relay output circuit open (no drive detected). Check relay, fuse, wiring and control module.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

B28F0 B28F1 B2800 B2900 P0627
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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