Introduction:
The B1939 diagnostic trouble code (DTC) indicates a fault within the passenger airbag system, specifically a short to ground in the circuit for the passenger pressure switch. This switch plays a crucial role in determining whether the passenger airbag should deploy in a collision, based on the weight and presence of a front seat passenger. A short to ground in this circuit can lead to incorrect airbag deployment or a complete system failure, compromising passenger safety.
Table: B1939 Air Bag Passenger Pressure Switch Circuit Short To Ground Details
| Topic | Description | Potential Causes |
|---|---|---|
| Definition | Indicates a short to ground in the circuit of the passenger seat pressure switch. | Damaged wiring harness, faulty pressure switch, corroded connectors, shorted circuit within the airbag module. |
| Function of Pressure Switch | Determines if a passenger is present in the front seat and their approximate weight. | Allows the airbag control module to adjust airbag deployment force or disable the airbag altogether (if appropriate). |
| Symptoms | Airbag warning light illuminated, passenger airbag may not deploy in a crash, possible unintended deployment. | Airbag system disabled, incorrect weight readings, error messages on diagnostic scan tool. |
| Affected Components | Passenger seat pressure switch, wiring harness, airbag control module (ACM). | Connectors, fuses, ground points, and potentially other sensors within the airbag system. |
| Troubleshooting Steps | Visual inspection, multimeter testing, wiring diagram analysis, scan tool diagnostics. | Component replacement (pressure switch, wiring harness), connector cleaning, ACM reprogramming. |
| Severity | High - compromises passenger safety in the event of a collision. | Could lead to serious injury or death if the airbag system doesn't function correctly. |
| Common Vehicle Brands | Widely applicable across various manufacturers (Ford, GM, Chrysler, Toyota, Honda, etc.). | Specific wiring and component designs vary by manufacturer and model year. |
| Location of Components | Pressure switch is typically located within the passenger seat cushion. Wiring runs under the seat. | ACM is usually located under the center console or dashboard. Ground points are found throughout the vehicle. |
| Tools Required | Multimeter, scan tool, wiring diagram, basic hand tools. | Terminal crimpers, wire strippers, dielectric grease, replacement connectors. |
| Related DTCs | B1938 (Open Circuit), B1937 (Circuit High), other airbag system codes. | These codes may indicate related issues within the same circuit or elsewhere in the airbag system. |
| Typical Resistance Values | Resistance should be within the manufacturer's specified range; a near-zero reading indicates a short. | Consult the vehicle's service manual for specific resistance values for the pressure switch circuit. |
| Actuator Type | Piezoelectric pressure sensor or strain gauge sensor. | Convert pressure into an electrical signal. |
| Wiring Color Codes | Varies by manufacturer; consult the wiring diagram for specific color codes. | Color codes are essential for identifying the correct wires when troubleshooting. |
| ECM/PCM Involvement | While the ACM primarily controls the airbags, the ECM/PCM may monitor the overall system. | The ECM/PCM may store related diagnostic information. |
| Potential for Fire | Low, but a severe short circuit can potentially damage wiring and cause a fire hazard. | Inspect for melted or burned wires during troubleshooting. |
| Warranty Considerations | Airbag system components are often covered under the vehicle's warranty. | Check the warranty terms and conditions for specific coverage details. |
| DIY Repair vs. Professional | Diagnosing and repairing airbag systems can be complex and dangerous; professional help is recommended. | Improper repairs can render the airbag system ineffective or cause unintended deployment. |
| Alternative Names | Passenger Occupant Detection System (PODS) circuit short to ground. | This term is often used interchangeably with the passenger pressure switch circuit. |
| Impact on Insurance | Improper airbag function can affect insurance claims in the event of an accident. | Ensure that the airbag system is functioning correctly for maximum safety and proper insurance coverage. |
| Testing Procedures | Using a multimeter to check for continuity between the circuit wire and ground. | Inspect the pressure switch harness connections for corrosion and damage. |
Detailed Explanations:
Definition: The B1939 DTC signals that the electrical circuit connected to the passenger seat pressure switch is experiencing a short to ground. This means that the circuit is unintentionally making contact with the vehicle's chassis or another grounded component, diverting the electrical current.
Function of Pressure Switch: The passenger seat pressure switch is a critical component of the airbag system. It measures the pressure exerted on the seat cushion, allowing the airbag control module (ACM) to determine if the seat is occupied and estimate the occupant's weight. This information is vital for deciding whether to deploy the passenger airbag and, if so, at what force.
Symptoms: The most common symptom of a B1939 code is the illumination of the airbag warning light on the instrument panel. Other possible symptoms include the passenger airbag failing to deploy during a collision or, in rare cases, unintended airbag deployment. The vehicle's diagnostic scan tool will also report the B1939 DTC.
Affected Components: The primary components affected by a B1939 code are the passenger seat pressure switch itself, the wiring harness connecting the switch to the ACM, and the ACM. The wiring harness includes the connectors, wires, and insulation that transmit the electrical signal. The ACM is the central control unit for the airbag system.
Troubleshooting Steps: Troubleshooting a B1939 code involves a systematic approach. Begin with a visual inspection of the wiring harness and connectors for any signs of damage, corrosion, or loose connections. Next, use a multimeter to test the continuity of the circuit and check for a short to ground. Consult the vehicle's wiring diagram to identify the correct wires and test points. A scan tool can be used to read the DTCs and monitor the pressure switch's readings.
Severity: The severity of a B1939 code is considered high because it directly impacts the safety of the passenger in the event of a collision. A malfunctioning airbag system can lead to serious injuries or even death. It is crucial to address this issue promptly and correctly.
Common Vehicle Brands: The B1939 code is not specific to any particular vehicle brand. It can occur in a wide range of vehicles, including those manufactured by Ford, GM, Chrysler, Toyota, Honda, and others. However, the specific wiring and component designs will vary depending on the manufacturer and model year.
Location of Components: The passenger seat pressure switch is typically located within the passenger seat cushion, often integrated into the seat frame or foam. The wiring harness runs underneath the seat, connecting the switch to the vehicle's main wiring system. The ACM is usually located under the center console or dashboard. Ground points are dispersed throughout the vehicle's chassis.
Tools Required: To diagnose and repair a B1939 code, you will need a multimeter, a diagnostic scan tool, a wiring diagram specific to the vehicle, and basic hand tools such as screwdrivers and pliers. Terminal crimpers, wire strippers, dielectric grease, and replacement connectors may also be necessary.
Related DTCs: Other DTCs that may be related to a B1939 code include B1938 (Open Circuit in Passenger Pressure Switch Circuit) and B1937 (Passenger Pressure Switch Circuit High). These codes indicate different types of faults within the same circuit. Other airbag system codes may also be present, indicating related issues elsewhere in the system.
Typical Resistance Values: The resistance of the passenger seat pressure switch circuit should be within the manufacturer's specified range. A near-zero reading indicates a short to ground. Consult the vehicle's service manual or wiring diagram for specific resistance values.
Actuator Type: The pressure switch typically uses either a piezoelectric pressure sensor or a strain gauge sensor. These sensors convert the pressure exerted on the seat into an electrical signal that the ACM can interpret.
Wiring Color Codes: Wiring color codes vary by manufacturer. Consult the vehicle's wiring diagram for specific color codes for the passenger seat pressure switch circuit. Using the correct color codes is essential for identifying the correct wires during troubleshooting.
ECM/PCM Involvement: While the ACM is the primary controller for the airbag system, the engine control module (ECM) or powertrain control module (PCM) may monitor the overall system for faults. The ECM/PCM may store related diagnostic information.
Potential for Fire: While the risk of fire is relatively low, a severe short circuit can potentially damage the wiring and cause a fire hazard. Inspect the wiring harness for any signs of melted or burned wires during troubleshooting.
Warranty Considerations: Airbag system components are often covered under the vehicle's warranty. Check the warranty terms and conditions for specific coverage details.
DIY Repair vs. Professional: Diagnosing and repairing airbag systems can be complex and dangerous. Improper repairs can render the airbag system ineffective or cause unintended deployment, potentially leading to serious injuries. Professional help is highly recommended.
Alternative Names: The passenger pressure switch circuit is sometimes referred to as the Passenger Occupant Detection System (PODS) circuit. This term is often used interchangeably with the passenger pressure switch circuit.
Impact on Insurance: Improper airbag function can affect insurance claims in the event of an accident. Ensure that the airbag system is functioning correctly for maximum safety and proper insurance coverage.
Testing Procedures To test for a B1939 code, use a multimeter to check for continuity between the circuit wire and ground. Disconnect the pressure switch and check the harness side. A reading of 0 ohms indicates a short to ground. Also, inspect the pressure switch harness connections for corrosion and damage, cleaning or replacing as necessary.
Frequently Asked Questions:
Question: What does the B1939 code mean? Answer: It means there's a short to ground in the passenger seat pressure switch circuit, preventing the airbag system from functioning correctly.
Question: Is it safe to drive with a B1939 code? Answer: It's not recommended. The airbag system may not deploy properly in an accident, compromising passenger safety.
Question: Can I fix the B1939 code myself? Answer: Airbag system repairs are complex and potentially dangerous. Professional diagnosis and repair are strongly recommended.
Question: How do I find the passenger pressure switch? Answer: It's typically located within the passenger seat cushion. Check the seat frame or foam.
Question: What tools do I need to diagnose a B1939 code? Answer: You'll need a multimeter, a scan tool, a wiring diagram, and basic hand tools.
Conclusion:
The B1939 code indicates a serious issue with the passenger airbag system, potentially compromising passenger safety. Due to the complexity and potential hazards involved, professional diagnosis and repair are highly recommended to ensure the airbag system functions correctly in the event of a collision.