B1939 code definition
The B1939 code is manufacturer-specific body code related to air bags. In this case, it means that the engine control module (ECM) has detected a fault with the passenger-side air bag pressure switch.
What the B1939 code means
A code B1939 will be stored when the ECM has detected a short to ground from the passenger-side air bag pressure switch.
What causes the B1939 code?
Several problems may cause a B1939 code including:
- Damaged or corroded electrical wiring and related components
- Damaged or defective passenger-side air bag pressure switch
- Passenger-side air bag module malfunction
- SAS control module malfunction
What are the symptoms of the B1939 code?
Symptoms of a B1939 code may include:
- Check engine light may illuminate
- Air bag light may incorrectly illuminate
- Air bag light may flash
- Passenger-side air bags may not inflate
- There may be no symptoms other than a stored B1939 code
How does a mechanic diagnose the B1939 code?
A mechanic may use several methods to diagnose a B1939 trouble code, including:
- Utilize an OBD-II scanner to check for a stored B1939 trouble code
- Visually inspect wiring and related electrical components for signs of damage, wear, or corrosion
- Inspect the passenger-side air bag module connector
- Inspect the passenger-side air bag pressure switch
- Inspect the wiring harness between the SAS control module and clock spring for short to the power supply
- Inspect passenger-side air bag module
- Perform SAS control module DTC inspection
Common mistakes when diagnosing the B1939 code
Due to the danger involved with repairing most items related to a vehicle’s air bag system, it is recommended to seek assistance from a professional for repair. If performing repairs yourself, be sure to follow all possible safety precautions and procedures.
How serious is the B1939 code?
Because a vehicle’s safe driving operation can be impacted due to faults that store a B1939 code, this code is considered a potentially serious code. When this code appears, it is recommended to immediately take your vehicle to your local service center or mechanic for repair and diagnosis.
What repairs can fix the B1939 code?
Several repairs can fix a B1939 trouble code and include:
- Replace damaged, shorted, or corroded wiring and related electrical components
- Replace damaged or defective passenger-side air bag pressure switch
- Replace damaged or defective wiring harness between SAS control module and clock spring
- Replace damaged or defective passenger-side air bag module
- Replace damaged or defective SAS control module
Additional information related to a B1939 code
It cannot be stressed enough that improperly handling a vehicle’s air bag system components can accidentally deploy the air bag modules and pre-tensioner seat belts, which can seriously injure you and others in the vicinity. Read all service warnings and cautions before handling air bag system components. Anything related to air bag repairs can be both difficult and dangerous, and is often best left to professionals for diagnosis and repair. If making any repairs at home, take care with the air bags when removed from the vehicle.
Need help with a B1939 code?
YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.
This article originally appeared on YourMechanic.com as B1939 OBD-II Trouble Code: Air Bag Passenger Pressure Switch Circuit Short to Ground and was authored by Parker Hill.