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Discussion Starter #1 (Edited)
First, the good stuff...

Center seat connector resistances [brackets include tested ranges]:
  • Occupancy Detection (white plug): 390 Ohm [360-400]
  • Seat Belt Pretensioner (half of yellow plug): 2.5 Ohm [2.3 - 3.2]
  • Seat Belt Buckle (half of yellow plug): 2300 Ohm [1900-4500]
59828


The longer story...

This has been beat to death on this forum, but as far as I can tell, there are no reported successes without purchasing another seatbelt buckle assembly ($280 MOPAR), or in rare cases, the "ebay dongle". Took me awhile to notice that. With countless hours dumped into this, I was at my wits end about to cave and purchase the MOPAR part or maybe hit up a junkyard for late-model FCA belt buckles.

The primary gotchya is that the seat belt switch is a Hall Effect sensor. Fucking Chrysler/FCA.
The Occupational Restraint Controller (OCR) applies a voltage to it every 100ms and reads the output current. If it is outside the expected range, your SRS light pops on after 2.5 seconds.

Notably, when you measure the switch resistance with a multimeter, you will find an open circuit whether the belt is buckled or unbuckled.
This is because the sensor requires a voltage across its leads to operate.

Couldn't find any spec on the Promaster Hall sensor but I found a datasheet for another hall-effect seat belt switch (attached).
Wondering if the switch could be spoofed with a resistor for a particular state, I used Ohms Law to calculate a substitution resistance. I assumed 12V "operating voltage" and 5mA output current:
12V/0.005A = 2400 Ohm

I was ready to test with a bunch of resistances and had set up a potentiometer to do so (pic attached). Miraculously, the first attempt nailed it.

Cycled ignition 3 times and the SRS light was off for the first time (10,000miles, 6 months) since removing the bench seat . Did not have to start engine. Dunno if I actually had to cycle ignition.

I did not unplug the battery for this. I used to, but came to the conclusion that the only thing we need to avoid is applying a voltage to an existing squib. Latent charge in the OCR could possibly do that so I would still recommend disconnection of battery before unplugging connectors from any seat. We are working only with resistors.


The occupant detection thing (white plug) measures 400-Ohm empty, begins registering the seat belt warning around 350 Ohm and goes down to 20 Ohm with a heavy person in the seat. I went with 390 Ohm as I did not want to risk a fault by going over 400 Ohm.
I have no code reader that can read SRS codes.

Other notes pertaining to misconceptions seen elsewhere in the forum:
  • The OCR system is "floating" as to prevent accidental discharge, so the ground is isolated from the chassis ground.
  • The short circuiting shunt is only applied on the seat-side of the yellow connector when it is disconnected. Not our problem here.
  • The Airbag system is almost certainly entirely disabled if the SRS light is on. If OCR is getting funky measurements, it does not want to risk accidental deployment.
OCR seat belt switch operation - From stolen Chrysler tech doc (posted elsewhere on forum)
59825


Big thanks to all the others who paved the way in other forum posts.

Good luck, hope this helps!
 

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First, the good stuff...

Center seat connector resistances [brackets include tested ranges]:
  • Occupancy Detection (white plug): 390 Ohm [360-400]
  • Seat Belt Pretensioner (half of yellow plug): 2.5 Ohm [2.3 - 3.2]
  • Seat Belt Buckle (half of yellow plug): 2300 Ohm [1900-4500]
View attachment 59828

The longer story...

This has been beat to death on this forum, but as far as I can tell, there are no reported successes without purchasing another seatbelt buckle assembly ($280 MOPAR), or in rare cases, the "ebay dongle". Took me awhile to notice that. With countless hours dumped into this, I was at my wits end about to cave and purchase the MOPAR part or maybe hit up a junkyard for late-model FCA belt buckles.

The primary gotchya is that the seat belt switch is a Hall Effect sensor. Fucking Chrysler/FCA.
The Occupational Restraint Controller (OCR) applies a voltage to it every 100ms and reads the output current. If it is outside the expected range, your SRS light pops on after 2.5 seconds.

Notably, when you measure the switch resistance with a multimeter, you will find an open circuit whether the belt is buckled or unbuckled.
This is because the sensor requires a voltage across its leads to operate.

Couldn't find any spec on the Promaster Hall sensor but I found a datasheet for another hall-effect seat belt switch (attached).
Wondering if the switch could be spoofed with a resistor for a particular state, I used Ohms Law to calculate a substitution resistance. I assumed 12V "operating voltage" and 5mA output current:
12V/0.005A = 2400 Ohm

I was ready to test with a bunch of resistances and had set up a potentiometer to do so (pic attached). Miraculously, the first attempt nailed it.

Cycled ignition 3 times and the SRS light was off for the first time (10,000miles, 6 months) since removing the bench seat . Did not have to start engine. Dunno if I actually had to cycle ignition.

I did not unplug the battery for this. I used to, but came to the conclusion that the only thing we need to avoid is applying a voltage to an existing squib. Latent charge in the OCR could possibly do that so I would still recommend disconnection of battery before unplugging connectors from any seat. We are working only with resistors.


The occupant detection thing (white plug) measures 400-Ohm empty, begins registering the seat belt warning around 350 Ohm and goes down to 20 Ohm with a heavy person in the seat. I went with 390 Ohm as I did not want to risk a fault by going over 400 Ohm.
I have no code reader that can read SRS codes.

Other notes pertaining to misconceptions seen elsewhere in the forum:
  • The OCR system is "floating" as to prevent accidental discharge, so the ground is isolated from the chassis ground.
  • The short circuiting shunt is only applied on the seat-side of the yellow connector when it is disconnected. Not our problem here.
  • The Airbag system is almost certainly entirely disabled if the SRS light is on. If OCR is getting funky measurements, it does not want to risk accidental deployment.
OCR seat belt switch operation - From stolen Chrysler tech doc (posted elsewhere on forum)
View attachment 59825

Big thanks to all the others who paved the way in other forum posts.

Good luck, hope this helps!
This is awesome. I was just about to order parts after my failed attempts from info others had tried and supposedly succeeded. I will be giving this a try this week.
 

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Discussion Starter #4 (Edited)
Which resistor did you actually use? 2200,2300 or 2400?
2287 Ohm was what I had a potentiometer set to when I initially got the SRS light to disappear.
I ultimately replaced it with a 2200 Ohm resistor as that is what I had on hand. Tested the whole range specified above with the pot tho.
OCR is probably looking for a range spanning at least a couple milliamps. Assuming 12V supply, the difference between 2400 and 2200 ohm resistor will be less than 0.5mA.
 

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2287 Ohm was what I had a potentiometer set to when I initially got the SRS light to disappear.
I ultimately replaced it with a 2200 Ohm resistor as that is what I had on hand. Tested the whole range specified above with the pot tho.
OCR is probably looking for a range spanning at least a couple milliamps. Assuming 12V supply, the difference between 2400 and 2200 ohm resistor will be less than 0.5mA.
I used a 2400 ohm and 2.5 Ohm as that is what I had on hand and no go. I'm using the seat sensor from the old bench seat.so I didn't mess with that. If I understand your potentiometer testing, this should have worked. Not sure what I'm missing.
 

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Discussion Starter #6
I used a 2400 ohm and 2.5 Ohm as that is what I had on hand and no go. I'm using the seat sensor from the old bench seat.so I didn't mess with that. If I understand your potentiometer testing, this should have worked. Not sure what I'm missing.
We can test the effectiveness of your seat belt buckle sensor resistor.
See if you can spoof the driver seat belt detector by putting your 2400ohm resistor across the driver-seat plug.
The seatbelt indicator light is your feedback tool. If you turn the ignition and the seatbelt light is not showing, the spoof is successful and your problem is elsewhere:

  • Test the continuity of seat sensor you took out - I've read that they are fragile.
  • Make sure you didn't reverse the 2.5ohm and 2400ohm resistor locations (see picture). Wire colorings are downright confusing. Go by orientation of the plug.
  • If you are shoving resistors into the plug pin-holes, it can be tricky to make contact. You could splice into the wire behind the plug and check continuity.
 

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We can test the effectiveness of your seat belt buckle sensor resistor.
See if you can spoof the driver seat belt detector by putting your 2400ohm resistor across the driver-seat plug.
The seatbelt indicator light is your feedback tool. If you turn the ignition and the seatbelt light is not showing, the spoof is successful and your problem is elsewhere:

  • Test the continuity of seat sensor you took out - I've read that they are fragile.
  • Make sure you didn't reverse the 2.5ohm and 2400ohm resistor locations (see picture). Wire colorings are downright confusing. Go by orientation of the plug.
  • If you are shoving resistors into the plug pin-holes, it can be tricky to make contact. You could splice into the wire behind the plug and check continuity.
I verified the seat sensor and I'm getting 403 ohms so I think that is OK. I'm also not getting a seatbelt warning light, which I think would illuminate if the old seat sensor was bad. I only have the SRS light on. I'll eliminate this sensor from the equation and re-test with a resistor.

I definitely had the resistors in the correct location. To eliminate any loose connections, I've soldered tips onto the resistors and alligator clips the the occupancy resistor and I will test tomorrow. Wish me luck!
60028
 

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I tried it with the above resistors and no dice. I also tried it swapping the occupancy sensor and the 403 ohm resistor, also no success. The SRS light remains on. I even disconnected the battery for an hour, just to see if that would help. It didn't of course. One odd thing. While strapped into the drivers seat, key on, I pulled the 403 ohm resistor off of the white plug. The seat belt light did not come on. I would think it should have. Without a SRS scan tool I'm not sure what exactly the computer thinks is going on.

I really had high hopes for this. This fix is the most clear and concise one I've seen to date with no ambiguity and test results at various resistances. I just can't figure out why its not working for me.
 

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Discussion Starter #9
One more stupid "are you sure" question: Are you sure the (existing) passenger bucket seat is completely good?
Are the plugs in tight?
Do you measure ~2.5Ohm across its pretensioner explosive-charge terminals and 400ohm across its occupancy detection (white plug) terminals?

The salvaged bucket seat I purchased actually had an exploded pretensioner charge (tests as open circuit). This is pretty common. You can tell because the seat belt buckle thing is all scrunched up compared to your driver seat. That explosion usually severs a wire for the seat belt buckle sensor, which would also throw an SRS light. It took me months to even notice this. Had a company replace the charge and fix the wire for like $45.
 

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Discussion Starter #10
**** man, I really want this to work for you and others as well. You down to try one more thing for me and see if it gives us any usable info?

I wasn't very clear on what I described in my last message RE: using "buckle seat belt light" as a test tool. I'll try again.
1) Note that when you, as the only vehicle occupant, activate the ignition, the "buckle your seatbelt" light shows until you strap in. (there is no occupancy sensor/white plug on the driver seat - its implied that there is a driver. This is one less variable to deal with while testing.).
2) Note also that I found that a resistor in the 2200ohm range simulates a BUCKLED seatbelt.

My suggestion for testing is to unplug the yellow seatbelt plug under the DRIVERS seat, and put your 2400ohm resistor across the DRIVER seat belt buckle terminals (like you are trying to do with the center seat).
Now turn on the ignition. Is the "buckle your seatbelt" light off immediately?

Do you see what I am getting at with this test? Basically tells you if 2400 ohm resistor is doing the trick. If "buckle seatbelt" light is not off, experiment with other resistors till you get it to turn off. this is pretty much what i did.


In regards to

One odd thing. While strapped into the drivers seat, key on, I pulled the 403 ohm resistor off of the white plug. The seat belt light did not come on. I would think it should have.
The occupancy detection sensor operates in the range of 20ohm (fat passenger) to 400ohm (empty seat). You effectively increased the resistance to infinity by removing the resistor. "open circuit". The only thing I'm sure that would do is be one more thing keeping that SRS light on.

In the interim, you would be better off using something 20-250Ohm that trips the "buckle your seatbelt" light, so then you will KNOW that this part of the system is NOT a cause of the SRS light..

Remember you need to have the driver buckle latched to see if the center seat is causing the 'buckle your seatbelt" light to show.

But before you mess wi hthe center seat more, I'd recommend experimenting with the driver seat as described.
 

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Thanks for your help on this. There are no stupid questions. Electronics are not my strong suit so all suggestions are welcome and appreciated. As far as the passenger seat, it came out of a working promaster. I was lucky to find a guy locally that wanted a bench. I did verify he had no warning lights on before we swapped. Also when we are rolling and the passenger unbuckles the new swapped passenger seat belt, the SB warning light comes on and chimes.

I was a little unclear before about using the drivers seat for testing but now I get it. If I can get the 2400 ohm resistor to fool the drivers SB warning, I'll know that resistor is OK and the issue is elsewhere and this resistor should be OK for the center seat.

I'm fairly confident the occupancy sensor is good. I've checked it multiple times and it's reading 403 ohms. This sensor came out of the bench I swapped and I was very careful when I removed it. Other folks who have done this have had success, on at least this part, with a 400 ohm resistor. Not sure if a few ohms over would be an issue on my sensor. I will try to test this sensor on the passenger seat to see if plugging into this will allow me to sit unbuckled without tripping the SB warning. That should tell me if is good or not.

As far as the pretensioner, if I probe the seat side of the plug on either of the bucket seats, should I be getting 2.5 ohms?
 

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Ok. I feel I'm making progress.

Driver Seat: I tested the 2400 ohm on the drivers side plug. Seat belt light remained on. So 2400 is not going to work. I also tried 2000 but that didn't work either. At least now I know what's going on. Maybe 2200 is the sweet spot.

Occupancy Sensor: Unplugged the passenger seat sensor and plugged in sensor from old middle seat. I had to trim the nubs off of the white sensor plug to allow it to fit into the black plug on the passenger seat. Sitting on passenger seat does not trigger the seat belt warning light. Pressing on the old sensor turns the light on. So the sensor is good and 400 ohms will definitely work in place of it.

Seat Pretensioner: Both seats are reading 2.2 ohms.

Based on these results it seems the seat belt latch sensor is the issue. think I'm going to try 2.2 or 2.3 ohm for the pretensioner and 2200 ohm for the seat belt latch.

At least now I can verify first on the drivers seat thanks to your useful tip.

BTW. Does the wattage of the resistor matter? The ones I have are 1/4 watt.
 

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Discussion Starter #13 (Edited)
I think 1/4Watt should be fine. its what i used.
Edit - just realized, the numbers in my initial post yield 12V * 0.005A = 0.060Watts, so yeah, shouldn't be a problem.
 

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Finally got a chance to test after my resistors came in. I initially just tried the 2200 ohm resistor (reading a tad low at 2160) in the center seat connector hoping to get lucky. No love. It did not turn off the ABS warning.

Then I moved to the drivers seat spoof. Plugged the 2200 into that connector and the seat belt warning did not go out. Conclusion: 2200 isn't doing it either.

At this point I think the best course of action is to hook up a potentiometer to the drivers side connector and see how many ohms is takes until the seat belt light goes off. I'm pretty sure the 2.5 ohm on the airbag and 400 ohm on the occupancy sensor are not an issue. Once I get the drivers seat spoof to actually work then I can move on to the airbag resister if it's still not working.

Trial and error with different resistors is driving me mad.
 

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This would be helpful if a blown buckle was used for the missing seat. Still hoping a resistor solution can be found rather than stowing a buckle assy under the seat. I'll post in that thread but I'm not entirely clear on how he got the blown buckle to work. He mentions a resistor and 82nF cap. Not sure what that is.
 

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Here is the latest.Using the drivers seat as a test bed to eliminate the occupancy detector from the equation, I installed a 2.5 ohm in the air bag connection and a 5K pot on the seat belt connection. Running through the full range of the potentiometer, the seat belt light remained on. I also ran the test on the missing center seat connection but oddly as soon as I turned on the ignition, the resistance jumped to 8000 ohms with the pot turned all the way down. I got the same results on the passenger bucket connector. Not really sure what to make of that.

Bottom line is this won't work on my van unless I've missed something or screwed up somewhere. It may me the difference in model year. Scribbler's is a 2015. Mine is a 2018.

Pics of my test setup on drivers seat.

.
60343
 

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While looking at my options for just caving and buying a buckle, it appears that PN 5RM76JXWAA is compatible with all model years and engine types. This would seem to suggest that this workaround should have worked on any model year or engine type.
 

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I was able to disable the driver side buckle successfully. Mine is a 2019 if it matters.

Resistance jumps when you turn the key because you can't measure the resistance in a live circuit w/ a common voltmeter.

Edit: Opps, I see hikerSteve linked my post already.
 
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