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Home / DTC / B1349 — Heated rear window relay short to positive

B1349 — Heated rear window relay short to positive

Detailed page for trouble code B1349.

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Code

B1349

ALFA ROMEO B — Body

Heated rear window relay short to positive

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

Causes

  • Short to battery positive on heated rear window relay control or power feed
  • Failed/shorted relay (internal short between coil and supply)
  • Damaged wiring or pinched harness near hatch/boot/roof area
  • Corroded or damaged relay connector or terminals
  • Faulty Body Control Module / relay driver output
  • Aftermarket accessory incorrectly tapped into the relay circuit

Symptoms

  • Heated rear window does not operate normally or remains on
  • Related fuses may blow or show evidence of overheating
  • Battery drain when vehicle is off (parasitic draw)
  • Interior warning lamp or message related to rear window heater
  • DTC B1349 stored; possible intermittent function of rear demister

What to check

  • Read freeze frame and freeze data with a diagnostic scan tool; confirm current status of the code
  • Visually inspect relay, relay socket and associated fuses for heat damage or corrosion
  • Inspect wiring harness between relay, switch, rear window grid and battery for chafing, damage or aftermarket taps, especially at trunk/hatch hinge areas
  • With ignition off, unplug the relay and inspect pins for corrosion, melted insulation or shorts
  • Measure voltage at relay control pin with ignition on and with demister commanded off and on using a multimeter or oscilloscope
  • Check continuity from relay control pin to BCM and to constant positive feed to identify unintended connections

Signal parameters

  • Control line expected: ~0 V (low) when OFF; ~battery voltage (≈12–14 V) when relay commanded ON
  • Power feed to relay: battery voltage (≈12–14 V) constant
  • Typical relay coil resistance (varies by relay) commonly around 50–200 Ω (check specific relay spec)
  • Expected coil current when energized depends on coil resistance; typically 0.1–2 A (use relay spec)
  • Fault condition: battery voltage present on control/driver pin when relay should be OFF

Diagnostic algorithm

  1. Retrieve code and relevant freeze frame data with a scan tool; record exact conditions when fault set
  2. Visually inspect relay, socket and fuse for heat, melting or corrosion; replace if visibly damaged
  3. With ignition off and battery connected: disconnect the heated rear window relay; clear the code and see if it returns — if it does with relay removed, suspect wiring or MODULE output
  4. With wiring diagram, identify the relay control wire and backprobe it. With ignition on, command the demister ON/OFF and observe voltage on the control pin. Note if voltage is present when commanded OFF (indicates short to positive or stuck driver)
  5. If voltage present when OFF, disconnect the harness at convenient intermediate connectors and retest to isolate the section with the short. Pay attention to trunk/hatch hinge areas for chafe points
  6. Inspect and isolate any aftermarket accessories tied to the rear demister circuit; disconnect and retest
  7. If fault is tied to relay only (no external short), replace relay and retest. If fault persists with known-good relay removed, suspect BCM/driver output — consult module diagnostics and perform module-level tests
  8. If BCM/driver suspect, verify grounds and supply voltages, check for software updates, and follow manufacturer module repair/replacement procedures. Replace wiring or connector parts as needed. After repairs, clear codes and verify repair by cycling the function several times and by a road/usage test to ensure no parasitic draw
  9. Always follow safety procedures: if performing voltage/isolation tests, use appropriate PPE, avoid shorting terminals, and if major wiring repairs are required disconnect battery before performing splices or connector replacements

Likely causes

  • Damaged insulation allowing contact with constant 12V feed (harness rubbing or chafing)
  • Relay stuck or internally shorted, tying control pin to positive
  • Connector corrosion allowing conductive path to battery positive
  • Incorrectly installed aftermarket accessory (rear window accessory, amplifier, etc.) connected to relay feed
  • Faulty BCM output stage that is sourcing voltage when it should be off

Fault status

⚠️ Status
Heated rear window relay control circuit fault: short to positive detected (B1349). Possible short or stuck relay tying control to battery voltage.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

B1348 B1350 B1310 B1320 B13A0
89

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