B1399

What Does Code B1399 Mean?

Diagnostic Trouble Code (DTC) B1399 signifies an detected open circuit within the driver’s side power window one-touch window relay system. This code is typically set by the Body Control Module (BCM), Driver’s Door Module (DDM), or a similar dedicated power window control module, depending on the vehicle’s architecture. Modern power window systems, especially those with “one-touch” or “auto-up/auto-down” functionality, rely on dedicated relays or integrated relay drivers within a control module to provide the necessary high current for the window motor. These relays allow the module to briefly apply power to move the window fully up or down with a single press of the switch, often incorporating anti-pinch technology monitored via Hall effect sensors or current sensing.

The control module continuously monitors the electrical integrity of this relay circuit. When an open circuit is detected, it means the module senses an abnormally high resistance or a complete break in the electrical pathway leading to or from the relay coil, or within the relay’s power contact circuit itself. This prevents the relay from being energized or from passing current effectively, thereby disabling the one-touch function. The BCM/DDM interprets this lack of continuity or current flow as a circuit open fault, stores the B1399 code, and often defaults the window operation to manual mode, requiring the driver to hold the switch for the entire travel of the window.

Common Symptoms

• Driver’s Power Window One-Touch Function Inoperative: The primary symptom is the inability to use the auto-up or auto-down feature for the driver’s side window.
• Driver’s Power Window Operates Only in Manual Mode: The window may still function by holding the switch in the up or down position, but releases immediately upon switch release.
• Driver’s Power Window Completely Inoperative: In some cases, a critical open circuit could render the window completely unresponsive.
• Illumination of a Service or Warning Lamp: While B-codes do not typically trigger the Check Engine Light (MIL), a service light related to the body electrical system might illuminate.

What Causes the Code B1399?

• Faulty Driver’s Power Window One-Touch Relay: An internal open circuit within the relay coil or damaged contacts preventing current flow.
• Open Circuit in Wiring Harness: A broken, chafed, or severed wire in the power, ground, or control circuit leading to or from the one-touch relay. This often occurs in the flexible wiring loom within the door jamb.
• Corroded or Loose Electrical Connectors: Compromised connections at the relay socket, the window motor, the door module, or the window switch, leading to high resistance or an intermittent open circuit.
• Blown Fuse: A fuse protecting the power supply to the relay or the relay’s output circuit can cause an open.
• Faulty Driver’s Door Module (DDM) or Body Control Module (BCM): An internal fault within the module’s relay driver circuit, though less common, can manifest as an open circuit detection.

How to Diagnose and Troubleshoot

Diagnosing B1399 requires systematic electrical circuit testing. Prioritize safety by disconnecting the battery if working near airbag sensors or exposed wiring.

1. Verify the Complaint and Check for Related DTCs: Use an OBD-II scanner to confirm B1399 is present. Check for any other related body control or power window codes that might provide additional diagnostic direction. Clear the code and attempt to operate the one-touch window to see if it immediately returns.
2. Visual Inspection:
   • Carefully inspect the wiring harness running from the vehicle body into the driver’s door, specifically looking for pinched, cut, or chafed wires in the flexible boot.
   • Remove the door panel and inspect the wiring and connectors associated with the window switch, window motor, and the power window control module/relay (if external). Look for signs of corrosion, looseness, or damage.
   • Check all relevant fuses in the interior and under-hood fuse boxes that supply power to the driver’s power window circuit. Replace any blown fuses, but be aware that a blown fuse indicates an underlying short circuit.
3. Locate and Test the One-Touch Relay:
   • Identification: Consult the vehicle’s service manual or wiring diagrams to pinpoint the exact location of the driver’s power window one-touch relay. It may be a standalone relay, integrated into the DDM, or part of a multi-function relay block.
   • Relay Swap (if external): If the relay is external and accessible, swap it with a known good, identical relay from a non-critical circuit (e.g., horn, fog lights) if available and compatible. If the one-touch function returns, the original relay is faulty.
   • Relay Continuity Test (with DMM): If the relay can be removed, use a Digital Multimeter (DMM) to test its coil and contact continuity.
     • Measure resistance across the coil terminals; it should show a low, specific resistance (e.g., 50-150 ohms). An infinite reading indicates an open coil.
     • Measure continuity across the normally open (NO) contact terminals; it should show infinite resistance (open).
     • Apply fused 12V power and ground to the coil terminals (observing polarity if specified). Listen for a distinct click. While energized, the NO contacts should now show near-zero resistance (closed).
4. Circuit Continuity and Voltage Drop Testing (with DMM):
   • Power and Ground: With the relay (or DDM connector if integrated) disconnected, verify proper 12V battery voltage at the appropriate power supply terminals and a good ground at the ground terminals, as per the wiring diagram. Use the DMM.
   • Control Circuit: Backprobe the control signal wire from the DDM/BCM to the relay coil. While activating the window switch for one-touch operation, you should observe a momentary voltage change (e.g., 0V to 12V or 12V to 0V, depending on relay activation logic) at the coil control terminal.
   • Output Circuit: With the relay installed (or DDM connected) and the window switch activated for one-touch, measure voltage at the output terminal of the relay that feeds the window motor. Compare this to battery voltage; significant voltage drop indicates high resistance.
   • Wiring Continuity: Disconnect both ends of the suspect wiring section (e.g., between DDM and relay, or relay and motor). Measure resistance using the DMM; it should be near 0 ohms. Any reading above 5 ohms suggests an open or high resistance point. Also, check for short to ground or short to power.
5. Module Testing (If All Else Fails): If all external wiring, connectors, and relays test good, the fault may lie within the DDM or BCM. This typically requires specialized diagnostic tools or replacement of the module, followed by programming.

Recommended Repairs and Solutions

Once the root cause of the B1399 code has been accurately identified through thorough diagnostics, the following repairs are typically recommended:

• Replace Faulty Power Window One-Touch Relay: If the relay is found to have an internal open circuit or faulty contacts, replace it with a new, OEM-specified relay. Ensure the new relay is rated for the correct voltage and current.
• Repair or Replace Damaged Wiring Harness: If damaged wiring is identified, repair the affected section using appropriate automotive-grade wire and crimp connectors with heat shrink, or replace the entire damaged segment of the harness if extensive. Pay close attention to routing to prevent future chafing.
• Clean and Secure Corroded or Loose Electrical Connectors: Use electrical contact cleaner to remove corrosion from terminals. If terminals are severely corroded or deformed, they may need to be replaced. Ensure all connectors are fully seated and latched.
• Replace Blown Fuse: If a blown fuse was the culprit, replace it with a fuse of the correct amperage. Remember that fuses blow for a reason, so investigate for an underlying short circuit if the fuse blows again.
• Replace Driver’s Door Module (DDM) or Body Control Module (BCM): If all other components and wiring have been meticulously tested and confirmed to be in good working order, and the control module’s internal relay driver circuit is suspected, the DDM or BCM may need replacement. This often requires programming or “pairing” the new module to the vehicle, which typically necessitates factory-level scan tools.

Mechanic’s Tip: After any repairs involving the power window system, it is crucial to perform a window motor/module re-initialization or “learning” procedure. This process, unique to each vehicle manufacturer, teaches the control module the full travel limits of the window and is essential for the one-touch and anti-pinch functions to operate correctly. Failure to do so may result in continued inoperative one-touch features even after the B1399 code has been resolved.