B1347
Heated Backlite Relay Circuit Failure
Body Chassis/Safety Rear Defroster Control 🟢 Low — Fix at next service
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What This Actually Means
In plain language — no jargon

The heated rear window relay isn't working properly, so your defroster can't send power to warm up the backlite. Think of it like a light switch that's stuck or broken—the power wants to flow but the relay won't let it through.

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Symptoms You May Notice
3 known symptoms for this code
Rear window defroster doesn't heat up
Defroster button unresponsive or no indicator light
Possible electrical burning smell near rear of vehicle
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECU monitors voltage and current flow through the heated backlite relay circuit when the defroster is activated. It checks for proper relay engagement and continuous power delivery to the rear window heating element. A fault is detected when voltage drops unexpectedly, current draw is absent, or the relay fails to respond to activation commands.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Relay Coil Voltage 12V with activation command <10V or no voltage response
Backlite Circuit Current 15-30A during operation <5A or open circuit condition
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Fuse
Check and replace the heated backlite fuse in the fuse panel if blown.
2
Relay
Swap the heated backlite relay with an identical relay from another circuit to test if relay is faulty.
3
Wiring harness/connectors
Inspect and reseat all connectors at the relay, fuse, and rear window for corrosion or loose terminals.