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B1999 OBD-II Trouble Code: Passenger Side Side-Mount Air Bag Low Resistance on Squib

check engine light

B1999 code definition

The B1999 trouble code detects a side mount air bag inflation circuit error on the passenger side.

What the B1999 code means

The B1999 code is a standard OBD-II trouble code that signals a circuit malfunction in the side mount air bag inflator for the passenger seat. The side mount air bag is placed on the passenger side B-pillar, and inflates when the car is in an accident to provide protection for the passenger. Whenever the air bag control module, body control module, or powertrain control module (PCM) detect an abnormal or insufficient voltage reading from the side mount air bag inflator circuit on the passenger side, the B1999 trouble code may be triggered.

What causes the B1999 code?

The B1999 trouble code is usually caused by damaged or defective electrical components, such as blown fuses, open or loose connectors, or, most commonly, shorted wires. These damaged electrical components may be in the side mount air bag inflator, in the general side mount air bag system, or in the air bag control module. The code is also commonly caused by a defective squib, which is the component responsible for beginning the air bag inflation process, or a broken clockspring. Less common, but also possible, is a defective air bag control module. Finally, the code may also be triggered by a faulty PCM or body control module, though this is extremely rare.

What are the symptoms of the B1999 code?

If the B1999 code has been detected, it is likely that the side mount air bag on the passenger side will fail to inflate in the event of a crash. It is also possible that the entire air bag system will be inoperable, and no air bags will deflate should an accident occur. This code is commonly accompanied by an illuminated check engine soon Warning Light and air bag Warning Light on the gauge cluster.

How does a mechanic diagnose the B1999 code?

The B1999 code will be diagnosed using a general OBD-II trouble code scanner. A trustworthy mechanic will use the scanner to view the freeze frame data and gather information about the code. The scanner will also be utilized to see if there are any other trouble codes present. If numerous codes are detected, they will need to be diagnosed in the order that they appear in. The trouble codes will then be reset, the vehicle restarted, and the presence of the B1999 code checked for. If the code is no longer present, then it was likely detected erroneously, or was caused by an intermittent problem.

If the code remains detected, then the mechanic will begin by thoroughly inspecting all of the electrical components in the air bag system, particularly in the side mount air bag circuit and inflator. All damaged or compromised parts should be replaced. The squib should then be closely inspected, followed by the clockspring. If the problem has not yet been identified, a deeper inspection of the air bag control module will follow.

After the mechanic replaces or repairs any parts, the inspection should be paused while the codes are reset, the vehicle restarted, and the B1999 code checked for. By doing this, the technician will be informed as soon as the issue is resolved.

Common mistakes when diagnosing the B1999 code

The most frequently made mistake when diagnosing this code comes from a failure to properly adhere to the OBD-II trouble code diagnosis protocol. The protocol should be observed at all times, to increase the chances of an accurate and efficient diagnosis and repair.

It is fairly common for damaged wires to be overlooked, which often leads to unnecessary repairs of the side mount air bag squib, or the air bag control module.

How serious is the B1999 code?

A vehicle with the B1999 code will be drivable, and will not experience drivability problems. The side mount air bag on the passenger side will likely fail to inflate in an accident, however, and it is very possible that all of the air bags will experience failure. The air bag system is one of the most crucial safety features in the vehicle, and can save the life of the driver and passengers. Because of this, a vehicle with this code should not be driven until it has been inspected.

What repairs can fix the B1999 code?

Repairs for the B1999 trouble code are:

  • Replacement of wires, connectors, and fuses
  • Replacement of the side mount air bag squib
  • Replacement of the clockspring
  • In rare cases, replacement of the air bag control module
  • In very rare cases, replacement of the body control module or PCM

Additional comments for consideration regarding the B1999 code

This code is a manufacturer specific code, which means that the definition can vary based on the automaker. While the B1999 trouble code notes a side mount air bag circuit error in many cars, it can represent an entirely different body issue for other manufacturers. As always, the mechanic should be cognizant of the vehicle that is being inspected when diagnosing the B1999 code.

Need help with a B1999 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.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
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