B1402

What Does Code B1402 Mean?

DTC B1402 signifies a detected failure within the electrical circuit of the driver’s side power window ‘down’ switch. This code is typically set by the Body Control Module (BCM) or a dedicated Door Control Module (DCM), which monitors the electrical signals from the power window switches. The control module detects an abnormal voltage or resistance reading on the circuit associated with the ‘down’ function of the driver’s window switch. This abnormality could manifest as an open circuit (no signal when expected), a short to ground, a short to voltage, or an out-of-range resistance, indicating that the module is not receiving the correct input when the switch is actuated or is receiving an erroneous signal. This directly impacts the comfort and convenience subsystem, specifically preventing the driver’s side window from lowering as commanded.

Common Symptoms

• The driver’s power window does not respond when the ‘down’ button on the master switch is pressed.
• The driver’s power window operates intermittently, or only partially, when attempting to lower it.
• The driver’s master window switch may exhibit partial or complete loss of function for other windows or features, depending on the nature and location of the circuit failure within the switch assembly.
• Absence of illumination on the driver’s window ‘down’ switch, if the illumination circuit is integrated and affected by the primary fault.

What Causes the Code B1402?

• Faulty Driver Power Window Down Switch: Internal wear, corrosion, or breakage of the electrical contacts within the switch itself, preventing proper circuit completion or signal transmission.
• Damaged Wiring Harness: An open circuit, short to ground, or short to voltage in the wiring between the driver’s power window switch and the BCM/DCM. This is frequently observed in the flexible wiring conduit located in the door jamb due to repeated stress from opening and closing the door.
• Corroded or Loose Electrical Connections: Poor electrical contact at the driver’s window switch connector, the BCM/DCM connector, or any inline connectors within the door panel, leading to high resistance or intermittent signal loss.
• Faulty Door Control Module (DCM) or Body Control Module (BCM): An internal failure of the control module’s input circuit responsible for monitoring the driver’s power window switch signal. This is less common but should be considered after ruling out the switch and wiring.

How to Diagnose and Troubleshoot

Diagnosis of B1402 requires a methodical approach using appropriate diagnostic tools:

1. Visual Inspection: Begin by carefully inspecting the driver’s door panel, paying close attention to the power window switch assembly for any signs of physical damage, foreign objects, or moisture intrusion. Remove the door panel and inspect the wiring harness for pinched, chafed, or severed wires, particularly in the door jamb area and where the harness passes through grommets. Check for corrosion at the switch connector.
2. OBD-II Scan Tool Data: Connect an advanced diagnostic scan tool capable of communicating with the BCM/DCM. Access and monitor live data parameters related to the driver’s power window switch input. Actuate the ‘down’ switch and observe if the switch status changes on the scan tool. A lack of change or an erroneous status indicates a circuit issue.
3. Power and Ground Verification (DMM): Using a Digital Multimeter (DMM) and referring to the vehicle’s factory wiring diagram, identify the power and ground circuits supplying the driver’s power window switch. Test for proper voltage (typically 12V) on the power input wire and verify a solid ground connection. Inadequate power or ground can prevent switch operation.
4. Continuity and Resistance Test of Switch (DMM): Disconnect the electrical connector from the driver’s window switch. Using the wiring diagram, identify the specific terminals for the ‘down’ function. Test for continuity across the relevant terminals while actuating the switch to the ‘down’ position. Compare resistance readings to factory specifications. An open circuit or excessively high resistance indicates an internal switch fault.
5. Continuity and Short Circuit Test of Wiring Harness (DMM): With the switch disconnected and the BCM/DCM connector disconnected (if applicable), perform continuity tests on the signal wire(s) from the switch connector to the BCM/DCM connector. Look for an open circuit. Then, test for shorts to ground and shorts to battery voltage on the signal wire(s) by checking resistance between the signal wire and a known good ground, and between the signal wire and a constant 12V source, respectively.

Recommended Repairs and Solutions

Addressing DTC B1402 typically involves the following repairs, ordered by probability:

• Replace Driver Power Window Master Switch: If diagnostic tests confirm an internal fault within the switch (e.g., no continuity when pressed, incorrect resistance), the most common solution is to replace the entire driver’s side master power window switch assembly. Ensure the replacement part is compatible with the vehicle’s specific make and model.
• Repair or Replace Damaged Wiring Harness: If visual inspection or DMM tests reveal an open circuit, short, or high resistance in the wiring, precisely repair the damaged section using appropriate automotive-grade wire, crimp connectors, and heat-shrink tubing. For extensive damage, replacement of the entire door wiring harness may be a more reliable and durable solution.
• Clean and Secure Electrical Connections: If corrosion or loose pins are identified at any connector in the circuit, thoroughly clean the terminals using an electrical contact cleaner and a small brush. Ensure all connectors are securely seated and latched, verifying firm pin tension.
• Replace Door Control Module (DCM) or Body Control Module (BCM): If the switch and all associated wiring test perfectly within specifications, and live data from the scan tool still indicates a fault with the switch input, then the BCM or DCM itself may be faulty. Note that replacement of these control modules almost invariably requires programming or coding using a factory-level scan tool to integrate them with the vehicle’s existing systems.

Mechanic’s Tip: Always consult the vehicle’s factory service manual for model-specific wiring diagrams, connector pin-outs, and diagnostic flowcharts. These resources are invaluable for accurately identifying the correct wires and expected voltage/resistance values. Pay particular attention to the multi-pin connector in the door jamb, as it is a high-stress area prone to wire fatigue and breakage over time.