B1399 — Driver Power Window One Touch Window Relay Circuit Open

The diagnostic trouble code B1399 generally indicates an issue within the driver’s power window system, specifically related to the one-touch window relay circuit. This code suggests that the relay responsible for the one-touch window operation is either open or has a circuit fault. It’s important to note that label variations may differ between vehicle manufacturers, so always cross-reference with specific OEM documentation.

System affected: Power Window Control System
Severity: Moderate
Main symptoms: Window not operating in one-touch mode, relay sounding, or electrical issues in the door panel
Driveability: Limited (primarily related to the affected window)

Manufacturer variations for trouble code B1399

The B1399 code may be labeled differently depending on the vehicle manufacturer. Since manufacturers often assign their own coding or descriptive terms, here are some common variations:

Honda: DTC P0550 – Power Window Relay Circuit Open
BMW: 358E – Driver Window One Touch Relay Circuit Open
Volkswagen/Audi: 00972 – Window Control Module Circuit Error
Ford: B1399 – Power Window Relay Circuit Open (may vary in description)
General Motors: P1810 – Power Window Relay Circuit Issue

Remember, always consult the specific OEM factory repair information, as labels and code descriptions may vary slightly.

What does trouble code B1399 mean?

At its core, B1399 signifies that the Electronic Control Unit (ECU), which manages the power windows, has detected a problem in the circuit controlling the one-touch window relay. The ECU monitors the relay’s electrical circuit—including wiring, connectors, and the relay itself. When it detects an open circuit, a short circuit, or a malfunction in this system, the code is stored.

This fault typically occurs during the operation of the driver’s side window, particularly when using the one-touch function. For example, pressing the window switch in one-touch mode should send a signal that engages the relay to automatically lower or raise the window fully. If the relay circuit is compromised—due to wiring issues, relay faults, or connector problems—the system signals a fault, resulting in the B1399 code.

In the typical context, this code may appear if the relay is faulty, if the wiring harness is damaged, or if there’s a glitch in the control module. It often presents when attempting to use the one-touch window feature—experience suggests that the system’s inability to complete one-touch commands triggers the diagnostic trouble code.

Severity and risks of trouble code B1399

The severity of B1399 is generally considered moderate. While it often does not affect the overall drivability of the vehicle (since other electrical and mechanical systems are unaffected), it does inhibit the quick and convenient operation of the driver’s window. The risk primarily involves the inability to use the one-touch feature, which can be inconvenient or problematic for accessibility.

Potential risks include:

Failure of the window to operate in one-touch mode, which could lead to manual operation being the only option.
Possible electrical issues if the relay or wiring is damaged or shorted, potentially affecting other systems.
In rare cases, electrical faults could pose a risk of fire or further damage if left unaddressed.

Can the vehicle be driven with this code? Yes, typically, the vehicle remains drivable, but the driver’s window may not operate in one-touch mode, limiting functionality.

Symptoms of trouble code B1399

When B1399 is active, several specific symptoms may manifest, primarily related to the window’s behavior. You might notice the following:

The driver’s side window does not respond when using the one-touch switch.
The window may require manual hold or no movement at all when using the switch.
The relay responsible for the one-touch operation may produce unusual clicking sounds or noise during operation.
Potentially, other electrical concerns within the door panel, such as flickering lights or door lock issues, if related wiring problems exist.
Warning indicators on the dashboard related to the power window system, depending on vehicle make and model.

Most likely causes of trouble code B1399

While diagnosing B1399, understanding the most common causes can greatly streamline the repair process. The causes typically include:

Faulty relay—The relay responsible for the one-touch window operation may have failed or become internal to the ECU, leading to an open circuit.
Damaged wiring or connectors—Corrosion, wear, or physical damage to the wiring harness within the door panel can interrupt the relay circuit.
Malfunctioning control module—The vehicle’s body control module (or equivalent) may have a fault affecting relay control signals.
Failed switch or switch wiring—The window switch itself or its wiring may be defective, preventing proper signals from reaching the relay.
Electrical short circuit—A short circuit within the door wiring can cause circuit open detections and relay issues.

How to diagnose trouble code B1399

This diagnostic process involves systematic checks to isolate the fault. Always start with visual inspections before moving to electrical tests.

Visual Inspection: Check the wiring and connectors around the driver’s door and window switch for corrosion, damage, or loose connections.
Relay Check: Locate the relay associated with the one-touch window system, and test or replace it to see if the fault clears.
Live Data Monitoring: Use an OBD-II scan tool to observe the relay control signals and verify if the relay is being activated when pressing the switch.
Continuity Tests: Conduct continuity tests on wiring harnesses to ensure there are no open circuits or shorts.
Control Module Diagnostics: If applicable, run OEM-specific diagnostics to check the body control module and related controllers for faults.

Possible repairs for trouble code B1399

Based on diagnostics, repairs for B1399 often involve replacing or repairing faulty components. Here are probable fixes:

Replace the relay—A common and straightforward fix; this is generally a basic repair requiring only the replacement of the relay (professional help recommended).
Repair wiring or connectors—Wiring harness repair, replacement of damaged sections, or cleaning corrosion is typically a professional job.
Correct switch issues—If the window switch is defective, replacing it can restore normal operation.
Control module reprogramming or replacement—In cases of control module failure, reprogramming or replacing the module may be necessary (professional expertise required).
Address electrical shorts—Fixing shorts or damaged wiring to prevent future circuit faults (professional diagnosis recommended).

Vehicles commonly associated with trouble code B1399 in Europe

The B1399 code can be found across multiple makes and models, especially those with advanced power window controls. In Europe, vehicles from the following brands are more frequently associated with this fault:

Volkswagen Group: Volkswagen, Audi, SEAT, Škoda
Ford
BMW
Mercedes-Benz
Peugeot and other PSA group vehicles

The prevalence may depend on the age of the vehicle and usage conditions.

Frequent mistakes with trouble code B1399

When diagnosing or repairing B1399, technicians and vehicle owners should be cautious of common mistakes:

Assuming the relay is functional without testing—Replacing relays blindly can lead to misdiagnosis; always confirm with testing.
Overlooking wiring and connector integrity—Ignoring potential wiring damage or corrosion can result in recurring faults.
Confusing relay control signals with power supply issues—Ensure the problem is isolated to the relay circuit, not power supply faults.
Ignoring OEM specifications and wiring diagrams—Using generic solutions without proper reference can complicate diagnosis.

Quick FAQ — trouble code B1399

Can this code disappear on its own? It is unlikely; unless the cause was temporary contact issues or moisture, the fault typically persists until repaired.

Can I keep driving? Generally, yes. The vehicle remains operational, but the driver’s window may not work in one-touch mode, which could affect convenience.

Why does the code return after clearing? If underlying wiring issues, faulty relays, or control module problems are unresolved, the code may reappear after reset. Proper diagnosis and repair are essential for a lasting fix.