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Home / DTC / B28F1 — Window relay output:short to BAT

B28F1 — Window relay output:short to BAT

Detailed page for trouble code B28F1.

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Code

B28F1

MITSUBISHI B — Body

Window relay output:short to BAT

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

Causes

  • Wiring damaged and shorted to battery voltage (pin-to-B+) on the window relay output circuit
  • Faulty power window relay stuck closed or contacts welded
  • Shorted output transistor or driver inside the body control module / window ECU
  • Corroded or bridged connector pins at relay, motor, or ECU
  • Aftermarket accessory or recent repair that tapped into the circuit incorrectly

Symptoms

  • Window operates unexpectedly or remains powered when switch is off
  • Blown fuse on power window circuit or repeated fuse failure
  • Battery drain when ignition off
  • DTC stored and possible loss of window control or erratic window operation

What to check

  • Retrieve all stored codes and freeze-frame data; record conditions when code set
  • Visually inspect wiring, connectors, and relay for heat damage, melting or corrosion
  • Check fuses for the power window circuit and any associated relays
  • With ignition OFF, measure resistance between the relay output wire and battery positive to check for a short
  • Backprobe relay output terminal with ignition ON/OFF to verify voltage state (compare to expected)
  • Disconnect window motor or relay output and confirm whether the fault code clears

Signal parameters

  • Expected (relay output OFF): ~0 V at relay output/wire
  • Expected (relay output ON): battery voltage (~11–14 V) at relay output/wire while operating
  • Fault condition: battery voltage present at output when relay/off or ignition off
  • If a short, measured continuity to B+ with ignition OFF (very low resistance)

Diagnostic algorithm

  1. Read and record DTC(s) and freeze-frame; check for related body network codes.
  2. Visually inspect wiring, connectors, relay socket, and window motor connectors for damage, melted insulation or corrosion.
  3. With ignition OFF, disconnect the window motor connector and the window relay connector. Check if the DTC clears after clearing codes; if it clears, the short is likely downstream (motor or harness).
  4. Backprobe the relay output terminal with ignition OFF and measure resistance to battery positive. Low resistance indicates a short to B+. If present, trace harness for chafing, pin contact with chassis or adjacent B+ feed.
  5. With ignition ON, backprobe the relay output and monitor voltage while operating the switch. Confirm output behaves: 0 V when off, ~battery voltage when on. If voltage is present while off, suspect relay stuck or internal module short.
  6. Swap with a known-good identical relay (if removable) and retest. If swapping clears the fault, replace the relay.
  7. If relay swap does not help and wiring checks show no external short, suspect internal fault in the body control/window ECU. Isolate and bench-test or consult manufacturer guidance for module testing and replacement.
  8. After repair, clear codes and perform multiple cycle tests of windows; verify no recurring codes and inspect for proper function.
  9. Safety note: avoid creating shorts while probing. Disconnect the battery when performing repairs on wiring harnesses; follow vehicle manufacturer safety procedures.

Likely causes

  • Short between the relay output wire and a constant B+ feed (chafed harness, pin pushed into wrong terminal)
  • Failed relay contacts holding the feed to the motor
  • Internal short in the BCM/window control module output stage
  • Connector contamination causing unintended continuity to battery

Fault status

⚠️ Status
Window relay output circuit — short to battery voltage detected (open/short fault in window relay output).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0 - 3.0 hours

Similar codes

B28F0 B28F2 B2801 B2850
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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