Code
B1349
ALFA ROMEO
B — Body
Heated rear window relay short to positive
Views:
UK: 2
EN: 3
RU: 1
AI status
Completed
Completed
100%
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
- Retrieve code and relevant freeze frame data with a scan tool; record exact conditions when fault set
- Visually inspect relay, socket and fuse for heat, melting or corrosion; replace if visibly damaged
- 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
- 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)
- 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
- Inspect and isolate any aftermarket accessories tied to the rear demister circuit; disconnect and retest
- 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
- 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
- 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
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Code
B1349
FIAT
B — Body
Heated rear window relay short to positive
Views:
UK: 2
EN: 4
RU: 2
AI status
Completed
Completed
100%
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
- Retrieve code and relevant freeze frame data with a scan tool; record exact conditions when fault set
- Visually inspect relay, socket and fuse for heat, melting or corrosion; replace if visibly damaged
- 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
- 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)
- 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
- Inspect and isolate any aftermarket accessories tied to the rear demister circuit; disconnect and retest
- 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
- 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
- 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
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Code
B1349
Other
B — Body
Heated Backlite Relay Short To Battery
Views:
UK: 9
EN: 14
RU: 10
AI status
Completed
Completed
100%
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
- Retrieve code and relevant freeze frame data with a scan tool; record exact conditions when fault set
- Visually inspect relay, socket and fuse for heat, melting or corrosion; replace if visibly damaged
- 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
- 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)
- 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
- Inspect and isolate any aftermarket accessories tied to the rear demister circuit; disconnect and retest
- 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
- 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
- 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
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