Code
B1349
FIAT
B — Body
Heated rear window relay short to positive
Views:
UK: 2
EN: 3
RU: 2
AI status
Completed
Completed
100%
Causes
- Damaged wiring or chafed insulation contacting battery positive conductors
- Shorted relay (internally stuck closed or contact welded)
- Incorrectly fitted or corroded connector causing backfeed to the control circuit
- Faulty rear window heating element or harness with internal short to positive
- BCM or relay driver transistor fault causing incorrect voltage on the control line
- Aftermarket accessory incorrectly tied into the circuit
Symptoms
- Heated rear window remains on continuously or comes on unexpectedly
- Blown fuse for rear window/heater circuit
- Battery drain with vehicle off
- Rear window not responding to switch because module has disabled circuit
- Related lamp or instrument cluster warnings
What to check
- Read and record faults from BCM with a scan tool; clear and attempt to re-create
- Visual inspection of relay, socket, connectors, and harness for damage or corrosion
- Check fuse(s) for the rear window heater for blown condition and correct rating
- Measure voltage at the relay control terminal with switch off and with heater commanded on
- Remove relay and check if system still receives battery voltage (backfeed check)
- Continuity/resistance check between control circuit and battery positive with power removed
Signal parameters
- Control signal voltage (relay coil/BCM output): Off ≈ 0 V, On ≈ battery voltage (11–14.5 V)
- Relay coil resistance (if applicable): typically tens to a few hundred ohms (vehicle-specific)
- Heater circuit current when active: typically several amps to tens of amps (depends on vehicle)
- No continuity between control circuit and battery positive with power removed (in healthy circuit)
Diagnostic algorithm
- Connect a scan tool, read all related codes and freeze frame; note conditions when B1349 set. Clear codes.
- With ignition off, visually inspect relay, socket, wiring harness, and rear window connector for damage, melted insulation, corrosion or aftermarket splices.
- Remove heated rear window relay. With ignition off, check for continuity between the relay control terminal and battery positive. There should be no direct short. If there is continuity, trace wiring to locate damaged section.
- With relay removed and ignition on, measure voltage at the relay control pin while commanding the rear window heater ON/OFF via the switch/scan tool. Off = ~0 V, On = ~battery voltage. If control pin is stuck at battery voltage with the relay removed, suspect BCM/driver or a backfeed.
- Inspect and measure voltage at the heater grid/harness and return path. Check for unexpected battery voltage where it should be low or open.
- Swap in a known-good relay (if available) and re-test to rule out an internally shorted relay.
- If wiring checks point to no harness fault and relay swap doesn’t clear the issue, test or replace the BCM/relay driver following manufacturer procedures; consult wiring diagram and powertrain/body schematics.
- After repair, clear codes, verify normal operation across several on/off cycles, and re-check for parasitic drain if battery concerns were present.
- Safety: remove battery negative when doing major harness repairs. Use insulated tools and avoid creating shorts while testing under power.
Likely causes
- Shorted wiring near relay or rear window harness (most common)
- Failed/heavily corroded relay stuck closed
- Connector corrosion/backfeed at relay socket
- Faulty BCM/relay driver (less common)
Fault status
Status
Heated rear window relay circuit shorted to positive — possible stuck relay or wiring short to battery. Service required.
Repair difficulty: Medium
Diagnostic time: 1-2 hours
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