B1347 — Heated Backlite Relay Circuit Failure

How much does it cost to fix B1347?

BCM repair or replacement — $300–$900; Replace the switch or actuator — $120–$450; Repair wiring or connectors — $80–$250. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

What are the symptoms of B1347?

Drivers most often notice: the affected function (locks, windows, lighting, wipers) works intermittently or not at all, no impact on engine operation in most cases, warning light on the dashboard.

What does OBD2 code B1347 mean?

Heated Backlite Relay Circuit Failure (B1347): a body electrical fault affecting the body electrical system. The car is usually drivable while you plan the repair. Most often caused by corroded or loose connectors, damaged wiring in door jambs or wet areas, blown fuse or failed relay.

Will B1347 clear itself?

Sometimes B1347 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

How do I diagnose B1347 myself?

Start with a scan: confirm B1347, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the heated backlite relay circuit, and verify the suspect component against live data before buying parts.

The rear window defogger—also called a heated backlite—relies on a relay that toggles power to the heating grid on your rear glass. The engine control module or body control module continuously watches this relay circuit, expecting specific voltage patterns when you turn the defogger on. When the module detects a reading that falls outside normal parameters—meaning the relay either fails to activate, shows an unexpected open circuit, or registers a short—the system logs trouble code B1347. Think of it as the module's way of flagging "something is wrong with the heated backlite control circuit and I don't like what I'm seeing."

Modern vehicles run dozens of these body electrical subsystems simultaneously, and the control module logs B1347 only after the anomaly persists across enough drive cycles to rule out a temporary glitch. Once stored, the module captures freeze frame data—essentially a snapshot of engine RPM, load, temperature, and vehicle speed at the exact moment the fault triggered. That snapshot is your roadmap for diagnosis. Code B1347 itself lives in the body electrical category of OBD2 diagnostics, which covers comfort and convenience systems rather than engine management.

Symptoms of B1347

• The rear window defogger refuses to activate or shuts off unexpectedly when turned on
• The defogger indicator light on the switch stays dark or flickers when pressed
• The dashboard body system warning light illuminates (check engine light may stay off in many cases)
• Intermittent operation—the defogger works sometimes but not others, especially in cold or damp weather
• No heat visible on the rear glass when the system should be active
• Other body electrical functions (power locks, windows, or exterior lights) may behave erratically alongside the defogger issue

Causes of B1347

• Corroded or loose electrical connectors at the relay, switch, or rear glass feed-through
• Blown fuse dedicated to the heated backlite circuit
• Failed relay controlling power to the rear window heating element
• Damaged wiring, particularly at flex points like door jambs or where wiring passes through the body
• Faulty defogger switch or actuator on the dashboard control
• Body control module itself malfunctioning and misinterpreting circuit status

How to Diagnose B1347

1. Hook up an OBD2 scanner and confirm B1347 is actively stored—not just in history. Record the freeze frame data carefully; it tells you what the engine was doing when the module flagged the fault.
2. Look for any related body electrical codes. Codes appearing alongside B1347 often point toward the actual root cause—a failing switch might throw its own code, or a BCM fault might generate multiple body codes at once.
3. Inspect the wiring harness and connectors tied to the heated backlite circuit. Focus on areas exposed to moisture or repeated flexing—door sills, hatch hinges, and anywhere wires pass through sheet metal.
4. Test the relay itself with a multimeter or swap it with a known-good unit if possible. Check for battery voltage at the relay coil and switched output sides.
5. Operate the defogger switch while monitoring voltage at the rear glass connectors. No voltage when switched on points toward a supply or ground problem upstream.
6. Clear the code, run a complete drive cycle under conditions similar to the freeze frame data, and verify B1347 does not reappear. If it returns, you are dealing with a hard failure rather than an intermittent issue.

Repair Options and Costs

The repair strategy depends entirely on which part of the circuit has failed:

• Relay replacement: $30–$120 for the part, $60–$120 labor if you pay someone to install it. This is often the culprit and the cheapest fix.
• Fuse replacement: Under $20 for the fuse itself—virtually free if you do it yourself.
• Wiring repair or connector replacement: $80–$250 depending on labor time and whether connectors need full replacement versus simple cleaning and pin reseating.
• Defogger switch or actuator replacement: $120–$450 for parts and labor combined on most models.
• Body control module repair or replacement: $300–$900 including programming and calibration on some vehicles where the BCM must be matched to the car.

Total Cost to Fix B1347

Most B1347 repairs fall between $80 and $900 depending on the root cause. If a blown fuse or bad relay is to blame, expect to spend under $150 total. Wiring repairs and connector work typically run $150–$250 at an independent shop. BCM replacement represents the high end and is usually only necessary after all other circuit components check out healthy. Always pursue accurate diagnosis before purchasing expensive modules—replacing the BCM when a $40 relay failed would be an expensive mistake.

Can You Drive with B1347?

Yes, in most cases you can continue driving. Body electrical codes like B1347 typically do not affect engine performance, transmission operation, or braking systems. The main safety consideration is reduced rear visibility during cold, foggy, or wet weather when you cannot clear condensation or frost from the rear window. If the defogger failure also involves exterior lighting or windshield wipers, address those promptly—especially in poor weather or if the central locking circuit is affected and leaves the vehicle in an unsecured state.

Related OBD2 codes

• B1300: Power Door Lock Circuit Failure
• B1301: Power Door Lock Circuit Open
• B1302: Accessory Delay Relay Coil Circuit Failure
• B1303: Accessory Delay Relay Coil Circuit Open
• B1304: Accessory Delay Relay Coil Circuit Short To Battery
• B1305: Accessory Delay Relay Coil Circuit Short To Ground