B1871 – Airbag System Malfunction (Multiple Definitions)

By Benjamin Jerew (Contact Me)
Last Updated 2016-10-31
ASE Master Tech

Trouble CodeFault LocationProbable Cause
B1871 Passenger Air Bag Disable Module Fault

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What Does Code B1871 Mean?

Because this is a B-code, this DTC (diagnostic trouble code) refers to a fault in one of the body control systems, such as climate control, airbags, power windows, or lighting. Because it is a B1-code, each manufacturer has its own definition for this DTC, and a few automakers reserve this DTC for the airbag system. Here are a few common definitions:

  • Toyota – Airbag System – Occupancy Sensor System Error (Front Passenger Seat w/o Passenger Air Bag Deactivation (PAD) Switch)
  • Mercedes-Benz – Airbag System – Right Front Side Airbag Ignition Squib Short Circuit
  • Ford / Mazda – Airbag System – Passenger Air Bag Deactivation (PAD) Switch Fault
  • General Motors – Driver Head Restraint Up Switch Circuit Range / Performance

What are the common causes of code B1871?

Depending on year, make, and model, DTC B1871 may have number of causes. Here are some of the most common.

  • Mercedes-Benz released a TSB to replace the airbag connector locks.

What are the symptoms of code B1871?

In case this DTC refers to the airbag system, the controller will disable it and illuminate the SRS (supplemental restraint system) warning light. This also means that, in case of an accident, the airbags will not inflate, even if the accident is severe enough to set them off.

In case this DTC refers to the power-adjustable seats, the headrest height will not be adjustable. You can still drive the vehicle, but a poorly-adjusted headrest could increase the risk of injury in case of an accident.

How do you troubleshoot code B1871?

Warning: Diagnosing the airbag system can be dangerous if you don’t have a current wiring diagram and knowledge of the system. Never use a test light or DMM (digital multimeter) to check resistance on an airbag circuit (those incased in yellow sheathing). The system could literally blow up in your face!

Troubleshooting this DTC will depend entirely on what vehicle and what system you are working with. After checking for applicable technical service bulletins (TSB), here are a few pointers:

  • Toyota – The SRS controller cannot see a signal from the occupancy sensor. Check all fuses feeding the SRS and sensor. Check for open or short circuits between the SRS controller and the sensor. Barring circuit problems, this may indicate a fault in the sensor or SRS controller.
  • Mercedes-Benz – The SRS controller sends a very small signal to the right front side airbag to see if it is ready to deploy. This DTC indicates that the SRS controller has detected a short circuit. Check that the airbag connector is seated properly, as a short-bar engages when the connector is disconnected. Check for SRS harness damage between the controller and the airbag.
  • Ford / Mazda – On most pickup trucks, there is PAD switch somewhere on the dash. Using the ignition key, you can disable the passenger airbag, in case you are using a rear-facing child seat because there is no other seating position for it. If you do not have a PAD switch, suspect the SRS controller. Otherwise, check the circuit between the SRS controller and the PAD switch for problems and repair as needed.
  • General Motors – Check fuses that feed the driver seat adjustment switches. Check the harnesses between the switches and controller.

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