Code
B1348
FIAT
B — Body
Heated rear window relay open circuit
AI status
Completed
Completed
100%
Causes
- Faulty or open relay coil or internal relay failure
- Broken/open wiring or connector between relay and Body Control Module (BCM)
- Corroded or loose relay socket/terminal
- Blown fuse supplying the relay
- Poor ground at relay or defogger circuit
- Faulty BCM or driver output (less common)
Symptoms
- Rear window defogger/heater does not operate
- Defogger indicator lamp may not illuminate or may flash
- No audible click from the relay when defogger is requested
- DTC B1348 stored in body/comfort module
What to check
- Scan for B1348 and read freeze-frame / related codes
- Verify fuse(s) for rear window heater/relay are intact
- Visual inspection of relay, socket and wiring for corrosion, damage or overheating
- Listen for relay click when defogger switch is activated
- Back-probe relay coil and switched terminals with defogger command active
- Measure continuity/resistance of wiring between relay and heated glass grid
Signal parameters
- Relay control (BCM) output: ~0 V when off, ~battery voltage (11–14.5 V) when commanded ON
- Relay coil resistance (typical, vehicle dependent): approx. 50–200 ohms (open coil indicates failure)
- Switched output terminal: battery voltage with relay energized; ~0 V or open when not energized
- Heated rear window grid resistance: usually low (tens of ohms to a few ohms) — check vehicle spec
- Coil current when energized: small (tens to a few hundred mA); contact current to grid can be high (several amps)
Diagnostic algorithm
- Connect a diagnostic scanner, confirm B1348 and note any related codes or freeze data.
- Visually inspect relay, socket and harness for corrosion, loose terminals, heat damage or water ingress.
- Check related fuse(s) for continuity; replace if blown and re-test. If fuse blows again, stop and diagnose short.
- With ignition ON, activate rear defogger and listen for relay click. If no click, back-probe the relay coil terminals:
- Verify BCM control pin changes from 0 V to battery voltage when switch is pressed.
- Check coil resistance with relay removed; open coil = replace relay.
- If BCM output is present but relay does not click, supply battery voltage directly to the relay coil to confirm relay operation (bench test) and verify switched output goes to battery voltage.
- If relay operates but grid doesn’t heat, measure voltage at relay switched terminal and at heated glass connector while energized to find open circuit in wiring or at grid.
- Check ground continuity for the defogger/relay ground path.
- Repair or replace damaged wiring, connectors or relay as indicated. After repairs clear codes and confirm proper operation and no reoccurrence of B1348.
- If wiring, fuse and relay are good but BCM does not command the relay, inspect BCM connectors and wiring; consider BCM testing/replacement per manufacturer procedure.
Likely causes
- Corroded/loose relay socket or connector at the relay
- Open wire or damaged harness to the relay coil or switched output
- Failed relay (coil open or contacts open)
- Blown fuse upstream of the relay
Fault status
Status
Heated rear window relay open circuit (B1348) — open circuit detected in rear window heater relay circuit.
Repair difficulty: Medium
Diagnostic time: 0.5-1.5 hours
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