B1350

What Does Code B1350 Mean?

DTC B1350 signifies a detected electrical fault within the control or power circuit of the heated backlite (rear window defogger/defroster) relay, specifically indicating a Short to Ground condition. The vehicle’s Body Control Module (BCM), or in some architectures, the Generic Electronic Module (GEM) or an integrated control unit, is responsible for monitoring this circuit. When the module attempts to energize the heated backlite relay, it expects to see a specific voltage range or current draw profile. If the BCM detects an abnormally low voltage reading across the relay control circuit, or an excessively high current draw that implies an unintended direct path to vehicle chassis ground, it interprets this as a short. This prevents the relay from being properly activated or deactivates it prematurely to protect the circuit, leading to the illumination of the Malfunction Indicator Lamp (MIL) or a service message, and setting code B1350. The primary subsystem affected is the rear window defogger/defroster system, rendering it inoperative.

Common Symptoms

• Rear window defroster/defogger element fails to activate or heat up.
• The heated backlite indicator light on the dashboard or HVAC control panel may not illuminate, illuminate briefly, or flash erratically.
• Repeated blowing of the fuse associated with the heated backlite circuit.
• In some cases of a constant short, a subtle, unexplained battery drain may occur over time.
• Warning messages related to the defroster system may appear on the vehicle’s information display.

What Causes the Code B1350?

• Faulty Heated Backlite Relay: An internal short circuit within the relay itself, where the control coil or power contacts inadvertently short to the relay’s metal casing or an internal ground path.
• Damaged Wiring Harness: A physical short to ground in the wiring for the heated backlite relay’s control circuit (e.g., the wire from the BCM to relay terminal 85 or 86) or its power circuit (e.g., the fused battery feed to relay terminal 30). This can result from chafing against metal components, pinching, rodent damage, or heat damage causing insulation breakdown.
• Corrosion or Water Intrusion: Significant corrosion within the relay socket or the associated electrical connectors, creating an unintended conductive bridge to ground. Water intrusion into the relay box or wiring harnesses can also lead to similar shorting conditions.
• Internal BCM/GEM Fault: Although less common, an internal malfunction within the Body Control Module or the integrated control unit itself could cause it to falsely detect a short or, in rare instances, provide an erroneous ground path internally.

How to Diagnose and Troubleshoot

Diagnosis of B1350 requires methodical electrical testing using a Digital Multimeter (DMM) and a comprehensive OBD-II scan tool.

1. Visual Inspection: Begin with a thorough visual inspection. Locate the heated backlite relay, typically found in the under-hood fuse box or an interior fuse panel. Inspect the relay, its socket, and the surrounding wiring harness for any signs of damage, such as chafing, pinching, melted insulation, corrosion, or burning. Check the fuse for the heated backlite circuit; if blown, do not replace it immediately without further diagnosis as it will likely blow again.
2. OBD-II Scan Tool Data: Connect an advanced OBD-II scan tool. Read any present, pending, or historical DTCs. Pay attention to freeze frame data, which records engine conditions at the moment the code was set. If available, use the scan tool’s bi-directional control functions to attempt to command the heated backlite relay ON/OFF. Monitor live data for the relay’s status and any associated voltage/current readings from the BCM.
3. Heated Backlite Relay Testing:
   • Relay Removal and Inspection: Carefully remove the heated backlite relay from its socket. Inspect the relay terminals for corrosion or damage.
   • Coil Resistance Test: Using a DMM set to ohms, measure the resistance across the relay’s control coil terminals (typically 85 and 86). Compare this reading to the manufacturer’s specifications (usually 60-120 ohms). An extremely low resistance (near 0 ohms) indicates an internal short within the coil.
   • Continuity to Ground (Relay Itself): Check for continuity between any relay terminal and the metal casing of the relay (if applicable). This would indicate an internal short.
   • Bench Test (Optional): Apply 12V and ground to the relay’s coil terminals (85 and 86) to audibly confirm it clicks. Then, with the coil energized, check for continuity across the switch terminals (30 and 87/87a).
4. Wiring Harness Short to Ground Test (Relay Socket):
   • Isolate the Circuit: With the heated backlite relay removed and the ignition OFF, use a DMM set to ohms.
   • Control Circuit Test: Identify the relay socket terminal corresponding to the BCM’s control signal to the relay coil (often terminal 86, but consult a wiring diagram). Place one DMM lead on this terminal and the other on a known good chassis ground. A reading close to 0 ohms indicates a short to ground in this wire.
   • Power Circuit Test: Identify the relay socket terminal that receives constant or switched battery voltage (often terminal 30). Test for continuity between this terminal and chassis ground. A low resistance reading indicates a short to ground in the power feed to the relay.
   • Isolation of BCM: If a short is found in the control wire, disconnect the BCM connector that provides this signal. Retest the wire for a short to ground. If the short disappears, the fault may be internal to the BCM. If it persists, the short is in the wiring between the relay socket and the BCM connector.
5. Voltage and Ground Presence (Relay Socket):
   • With the relay still removed, key ON, and the defroster commanded ON (if possible without the relay), use the DMM set to DC volts.
   • Verify 12V at the constant power terminal (30) and the BCM’s control signal terminal (85 or 86, depending on the design for either power or ground activation).
   • Verify a good ground connection at the appropriate ground terminal (85 or 86).

Recommended Repairs and Solutions

The repair strategy for B1350 is directly dependent on the root cause identified during diagnosis:

1. Replace the Heated Backlite Relay: If the relay itself is determined to be internally shorted, not switching, or exhibiting incorrect coil resistance, replace it with a new, OEM-equivalent relay. Ensure the new relay matches the original’s specifications (e.g., amperage rating, voltage, and pin configuration).
2. Repair or Replace Damaged Wiring Harness: If the diagnosis points to a short to ground in the wiring harness, the damaged section of wire must be meticulously repaired.
   • Locate and Isolate: Trace the affected wire to pinpoint the exact location of the short.
   • Sectional Repair: Cut out the damaged section. Splice in a new piece of wire of the identical gauge and type using appropriate soldering techniques (e.g., western union splice) and heat-shrink tubing for a robust, moisture-resistant connection. Avoid using crimp connectors where possible, especially in areas exposed to vibration or moisture.
   • Full Harness Replacement: In cases of extensive damage or multiple short circuits within a critical harness, full harness replacement might be the most reliable, albeit more expensive, solution.
   • Protection: Reroute the repaired/replaced wiring to prevent future chafing or damage, using conduit, loom, and zip ties as necessary.
3. Clean or Repair Corroded Connectors: If corrosion in the relay socket or connectors is the cause, thoroughly clean the affected terminals using electrical contact cleaner and a small wire brush. If the corrosion has led to severe terminal damage or loss of spring tension, the connector pigtail or the entire connector housing may need to be replaced.
4. BCM/GEM Replacement: If all other components (relay, wiring, and fuses) test conclusively good, and diagnostic procedures unequivocally indicate an internal fault within the Body Control Module or integrated control unit, then replacement of this module will be necessary. This often requires specialized programming or calibration by a dealership or a shop equipped with manufacturer-specific diagnostic tools to ensure proper vehicle function and to marry the new module to the vehicle’s network.