Seat belt warning light and chime not working

PCDJ64

MEMBER
2002 CHEVROLET TRAILBLAZER
4.2L
6 CYL
4WD
AUTOMATIC
209,000 MILES

There is no light on the dash or chime when the seat belt is unbuckled.
There is no light with the key turned to run when the other lights come on.
the LED for the seat belt in the cluster is good, there are no bad solder connections, all of the other chimes work.
tried unplugging the seat belt connector on the driver seat and it still does nothing.

There is no fuse for the seat belt warning, no relay or other replaceable part.

5 Replies

CARADIODOC

MECHANIC
33,757 POSTS

There isn't much to this circuit. Start by unplugging the connector at the SDM, then use an ohm meter to check the continuity of the seat belt switch circuit from terminal A15 to ground. Check if it switches between open and closed when you attach the seat belt. If it switches properly, the module is the best suspect.

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Saturday, January 18th, 2020 AT 1:59 PM

PCDJ64

MEMBER
127 POSTS

Thank you for the reply.
I didn't test any of the connections yet but tried something to see if it would do anything.
I plugged in a known dead SDM that has no com and the seat belt light functions and turns off when the seat belt is clicked in. The airbag light of course stayed lit because of no com but the other light worked fine.
I think this tells me that the wiring is okay and that I have a bad SDM, thing is I have the one that is original, a good matching number spare and neither lights the seat belt or runs chime.

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Monday, January 20th, 2020 AT 2:22 PM

CARADIODOC

MECHANIC
33,757 POSTS

Don't have an answer for that, but it sure looks like you verified the wiring and switch are okay.

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Monday, January 20th, 2020 AT 4:36 PM

PCDJ64

MEMBER
127 POSTS

It was a fluke that the no com SDM illuminated the seat belt light and the known good one didn't.
Turns out the light would go back off whether or not I connected the seat belt.
Problem ended up being broken wires at the buckle which I fixed with a junkyard part, took 3 tries to find one with good wires.
With the replacement buckle there is a chime when I first start the truck that was not present before and the light tests and then flashes until seat belt is buckled.
Thank you for the help, the diagrams came in handy for tracing the problem with my meter.

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Wednesday, January 22nd, 2020 AT 12:43 PM

CARADIODOC

MECHANIC
33,757 POSTS

Dandy. Happy to hear you solved it.

As a point of interest, on my skid steer, the starter will not engage unless the seat belt is fastened. Once running, the pedals will stop working when the seat belt is unhooked. Also, the starter and pedals won't work if the seat belt is constantly left connected behind the driver. The computer insists on seeing the seat belt unbuckled, then buckled, to insure no one bypassed the switch in the latch. Some cars use a similar system that prevents you from keeping the seat belt buckled behind you at all times. From your description, it sounds like your car has something similar going on.