Underdog's Occupant Detection System Bypass for Aftermarket Seats (MY06+ Style)

[Underdog]

Copying this information over from my build thread to make it easier to find. This modification came about when I installed Bride seats in my 2006 Legacy, and needed a way to bypass the occupant detection system and get rid of the airbag light on the dash. The original post was here if you'd like to see info about the Brides elsewhere in that thread, but the ODS Bypass Module and other airbag light information has been reformatted and moved to this thread for clarity.

Note: These modifications can affect the operation of your airbag system and if you choose to do it you are doing so at your own risk! Death or serious injury may occur if the airbag system does not function as designed!

To summarize, there are three things that must be done to prevent an airbag light with aftermarket seats:

1. Delete the airbags themselves. -> Bend a 3.3ohm resistor as shown below and insert into the airbag plug. Wrap with a quality electrical tape like 3M.

 

2. Transfer driver's seat position sensor (driver-side only, the sensor picks up a "flag" welded to the seat which disables the airbag when the seat is all the way forward). -> Remove sensor from bottom of seat by drilling out two rivets and unclipping the plug from the metal bracket. Coil up the pigtail and install plug into the floor harness.

 

3. Transfer occupant detection module and bypass occupant detection sensor. -> See below.

Note: This only applies for the MY06-09 which uses a bladder-style ODS; the MY05 uses four load cells which all communicate with the ODS module. For more information on the MY05 and a possible workaround to use the method below, please see 2005 Seat Swap to 2006+ with Full Airbag Function by @Harrimat.

The occupant detection module collects the signals from the passenger seat belt receptacle, the side airbag, and the occupant sensor. The module must be removed from the stock seat and plugged into the harness under the new seat. Be careful when drilling out the rivets that secure the ODS Module or you may drill through and pop the bladder in the seat - if you can get something behind the rivet to protect it, all the better. After you've removed the rivets you can unplug the ODS sensor and unclip the module plug from the bracket.

 

The sensor that detects the pressure in the bladder and communicates with the ODS module is a simple active 5V pressure sensor with three pins: 5V input, the signal output ("Vout"), and ground reference (GND). In order to vary the voltage on Vout we will create a switchable voltage divider by putting a resistor of fixed value between the 5V and Vout pins (R1), and resistors of two separate values - let's call them R2(empty) and R2(occupied) - between Vout and GND, with a switch selecting which resistor completes the circuit.

 

To simulate an empty seat R2 must be ~3x the value of R1. To simulate an occupied seat R2 must to be ~1/2 of R1 (the signal varies based on the weight of the person - the following is for a ~160lb person)

We can make things easy by selecting a value for R1 of 1kΩ, which means R2(empty) will be 3.3kΩ and R2(occupied) will be 470Ω, all common resistor values.

Now we can use a simple SPDT switch (preferably one that is ON-ON, with no OFF position in the middle) to toggle between two resistors for R2. Please see attached wiring diagram.

 

To make this mod plug-and-play I used the following parts:

Switch: "Baomain Car Toggle switch SPDT ON-ON 3 Pin 2 Position 12V 25A with waterproof cover for Auto Car"

Enclosure: "uxcell Waterproof Plastic Electric Project Case Junction Box (2.3x1.4-Inches, 5pcs)"

Connector: "GM Delphi / Packard - 3-Way GT 150 Receptacle Pigtail" (I ordered with 6" of wire on the pigtail and it was enough for my install, however you can order with any length and always cut it to fit.)

Otherwise you just need a few resistors and standard electrical work supplies (solder, heatshrink, wire loom, electrical tape, grommet, and hot glue/zipties for strain relief).

I used a step drill bit to drill 1/2" holes for both the grommet and switch. To keep things compact I soldered the R2 resistors directly to the terminals of the switch and encased them in hot glue to prevent movement that would lead to fatigue failure or a short circuit. The R1 resistor is soldered to the 5V and Vout wires from the receptacle pigtail, with the white wire connecting the Vout side to the common leg of the switch. Heatshrink everything and tuck it into place.

 

The completed module can now be plugged into the pressure sensor receptacle on the ODS Module harness. 3M double-stick tape was plenty to attach the enclosure to the frame rail of my Bride seat, and I added a ziptie for extra security.

 

With the switch mounted under the seat you can toggle between armed and disarmed, and everything behaves normally. Congratulations - you have completed the ODS bypass modification.

[08Spec_B]

Awesome write up! For the switch resistors, what W rating did you use? That is the one part thats I dont quite understand how its figured/calculated. 

 

[Underdog]

6 hours ago, 08Spec_B said:

Awesome write up! For the switch resistors, what W rating did you use? That is the one part thats I dont quite understand how its figured/calculated. 

 

Thanks! I used regular 1/4W resistors. It’s just a rating how much heat the resistor can dissipate, which is the product of voltage and amperage in a DC circuit. I don’t know the current draw of the sensor but figured it’s likely on the order of 10-100mA, which would mean a resistor power rating of 1/8W to 1W would be sufficient. Only downside to overspec’ing is cost and having to find room for the larger resistors. Of course going too low on the power rating means the resistor performance will degrade over time due to overheating. Haven’t had any issues since I did the mod in ~2018, but will certainly update here if that changes. 

[shralp]

On 1/31/2023 at 7:17 PM, Underdog said:

Copying this information over from my build thread to make it easier to find. This modification came about when I installed Bride seats in my 2006 Legacy, and needed a way to bypass the occupant detection system and get rid of the airbag light on the dash. The original post was here if you'd like to see info about the Brides elsewhere in that thread, but the ODS Bypass Module and other airbag light information has been reformatted and moved to this thread for clarity.

Note: These modifications can affect the operation of your airbag system and if you choose to do it you are doing so at your own risk! Death or serious injury may occur if the airbag system does not function as designed!

To summarize, there are three things that must be done to prevent an airbag light with aftermarket seats:

1. Delete the airbags themselves. -> Bend a 3.3ohm resistor as shown below and insert into the airbag plug. Wrap with a quality electrical tape like 3M.

 

2. Transfer driver's seat position sensor (driver-side only, the sensor picks up a "flag" welded to the seat which disables the airbag when the seat is all the way forward). -> Remove sensor from bottom of seat by drilling out two rivets and unclipping the plug from the metal bracket. Coil up the pigtail and install plug into the floor harness.

 

3. Transfer occupant detection module and bypass occupant detection sensor. -> See below.

Note: This only applies for the MY06-09 which uses a bladder-style ODS; the MY05 uses four load cells which all communicate with the ODS module. For more information on the MY05 and a possible workaround to use the method below, please see 2005 Seat Swap to 2006+ with Full Airbag Function by @Harrimat.

The occupant detection module collects the signals from the passenger seat belt receptacle, the side airbag, and the occupant sensor. The module must be removed from the stock seat and plugged into the harness under the new seat. Be careful when drilling out the rivets that secure the ODS Module or you may drill through and pop the bladder in the seat - if you can get something behind the rivet to protect it, all the better. After you've removed the rivets you can unplug the ODS sensor and unclip the module plug from the bracket.

 

The sensor that detects the pressure in the bladder and communicates with the ODS module is a simple active 5V pressure sensor with three pins: 5V input, the signal output ("Vout"), and ground reference (GND). In order to vary the voltage on Vout we will create a switchable voltage divider by putting a resistor of fixed value between the 5V and Vout pins (R1), and resistors of two separate values - let's call them R2(empty) and R2(occupied) - between Vout and GND, with a switch selecting which resistor completes the circuit.

 

To simulate an empty seat R2 must be ~3x the value of R1. To simulate an occupied seat R2 must to be ~1/2 of R1 (the signal varies based on the weight of the person - the following is for a ~160lb person)

We can make things easy by selecting a value for R1 of 1kΩ, which means R2(empty) will be 3.3kΩ and R2(occupied) will be 470Ω, all common resistor values.

Now we can use a simple SPDT switch (preferably one that is ON-ON, with no OFF position in the middle) to toggle between two resistors for R2. Please see attached wiring diagram.

 

To make this mod plug-and-play I used the following parts:

Switch: "Baomain Car Toggle switch SPDT ON-ON 3 Pin 2 Position 12V 25A with waterproof cover for Auto Car"

Enclosure: "uxcell Waterproof Plastic Electric Project Case Junction Box (2.3x1.4-Inches, 5pcs)"

Connector: "GM Delphi / Packard - 3-Way GT 150 Receptacle Pigtail" (I ordered with 6" of wire on the pigtail and it was enough for my install, however you can order with any length and always cut it to fit.)

Otherwise you just need a few resistors and standard electrical work supplies (solder, heatshrink, wire loom, electrical tape, grommet, and hot glue/zipties for strain relief).

I used a step drill bit to drill 1/2" holes for both the grommet and switch. To keep things compact I soldered the R2 resistors directly to the terminals of the switch and encased them in hot glue to prevent movement that would lead to fatigue failure or a short circuit. The R1 resistor is soldered to the 5V and Vout wires from the receptacle pigtail, with the white wire connecting the Vout side to the common leg of the switch. Heatshrink everything and tuck it into place.

 

The completed module can now be plugged into the pressure sensor receptacle on the ODS Module harness. 3M double-stick tape was plenty to attach the enclosure to the frame rail of my Bride seat, and I added a ziptie for extra security.

 

With the switch mounted under the seat you can toggle between armed and disarmed, and everything behaves normally. Congratulations - you have completed the ODS bypass modification.

Quick question for you Underdog. I may choose to swap in an aftermarket drivers seat into my ‘05 track car but still need airbag functionality until I can afford a cage.  Does this mean that I only need to do the first two steps of your three step process, (The resistor and seat position sensor), to make it work since I’m not touching the passenger seat? 

[Underdog]

3 hours ago, shralp said:

Quick question for you Underdog. I may choose to swap in an aftermarket drivers seat into my ‘05 track car but still need airbag functionality until I can afford a cage.  Does this mean that I only need to do the first two steps of your three step process, (The resistor and seat position sensor), to make it work since I’m not touching the passenger seat? 

Yep, you got it. Very easy if you’re only replacing the driver’s seat, and easy to reverse the mod as well.