Fix B0084 service airbag message
What is a B0084 trouble code?
The two basic codes are:
B0084 Front End Sensor 1
B0085 Front End Sensor 2
But you may have additional digits after the basic trouble code. Here’s what those additional numbers mean:
B0084 39 Electronic Front End Sensor 2 Internal Electronic Failure (Right)
B0084 3A Electronic Front End Sensor 2 Incorrect Component Installed (Right)
B0084 71 Electronic Front End Sensor 2 Invalid Serial Data Received (Right)
B0085 00 LF Side Impact Sensor No Additional Information
B0085 0F LF Side Impact Sensor Erratic
B0085 39 LF Side Impact Sensor Internal Electronic Failure
B0085 3A LF Side Impact Sensor Incorrect Component Installed
B0085 71 LF Side Impact Sensor Invalid Serial Data Received
How GM airbags work
GM uses a Sensing and Diagnostic Module (SDM) to monitor crash sensors, set trouble codes, illuminate the service airbag message and activate the airbags. The front end sensors (FES) (crash sensors) are located directly under the radiator, protected by a skid plate. The SDM sends power to the FES using a 2-wire circuit. The FES modulates current back to the SDM to send ID information, state of health and deployment commands. The SDM provides ground.
When you start the vehicle, the SDM sends power to the FES and the FES responds by performing an internal diagnostic. It then sends an ID to the SDM. If the FES sends the correct ID in less than 5-secs, it passes the test. From that point on, the FES communicates continually with the SDM. If the SDM loses contacts with the FES, it will attempt a reset up to two times by removing power and reapplying power. If it still can’t communicate, it sets a trouble code.
Diagnose and fix a B0084-00 service airbag message
GM C and K series trucks are known for setting airbag trouble codes B0084 and B0085, which also may set a service airbag message. Here are some tips to diagnose and fix a B0084 or B0085 code.
If you get any of these codes: B0083 00, B0084 00, B0085 00, B0086 00, B0087 00, B0088 00
• The front end sensor has been shorted to voltage, open, or shorted to ground.
• The front end sensor current has been above 23 mA for longer than 5 milliseconds.
• The SDM has not received a message from the front end sensor for more than 375 milliseconds.
If you get any of these codes: B0083 0F, B0084 0F, B0085 0F, B0086 0F, B0087 0F, B0088 0F
The SDM has received erratic messages from the front end sensor.
If you get any of these codes: B0083 39, B0084 39, B0085 39, B0086 39, B0087 39, B0088 39
• The SDM has received a Not Ok (NOK) message from the front end sensor.
• The SDM has not received a message.
• The SDM has received invalid serial data from the front end sensor.
If you get any of these codes: B0083 3A, B0084 3A, B0085 3A, B0086 3A, B0087 3A, B0088 3A
• The SDM has received an ID message from the front end sensor, which does not match the ID stored in
the SDM memory.
• The SDM has reset the front end sensor twice without detecting the correct ID message.
If you get any of these codes: B0083 71, B0084 71, B0085 71, B0086 71, B0087 71, B0088 71
The SDM has received invalid serial data from the front end sensor.
Check for corrosion
Corroded FES components are common on GM trucks. FES 1 is the right side sensor.
FES 2 is the left side sensor. Since these sensors are located up front under the radiator, they’re subjected to very harsh and corrosive conditions. So your first step should be to check for corrosion. Remove the skid plate to access the sensors. Check for corrosion on the sensor pins as well as corrosion on the connector pins. If you find corrosion, do NOT attempt to clean the pins. You must replace the connector with a new pigtail or replace the FES.
Next, check for water intrusion into the FES. If you detect corrosion or water, replace the pigtail and FES with new parts. If there’s no corrosion, swap the FES 1 With FES 2 and see if the code moves to the other side. The code and the same suffix should move to the other side. If the code doesn’t move, inspect the wiring harness.
Diagnose and fix B0085 trouble code
GM also uses crash sensors inside the front doors. These sensors detect air pressure change during a crash as the door is crushed. If the vehicle is used as a service or delivery vehicle, B0085 trouble codes are often traced to a break in the wiring in the hinge area where the wires flex. So start there.
©, 2018 Rick MuscoplatPosted on by Rick Muscoplat