1993 SC2 Automated shoulder belt dashboard light stays on

I have a 1993 SC2 with a manual transmission: This pertains to the driver side belt. These cars came with the automatic shoulder belts that open and close in sync with the status of the door. There is a light (shoulder belt icon) on the dash indicator bar that turns off when the shoulder belt is secured, as well as another light ("lab belt") that does the same when the waist belt is secured. The waist belt light works fine. I replaced the whole shoulder belt track and motor assembly this past November after the previous assembly had jammed partially open. After installing the replacement system the dash light worked correctly, however, as the winter months went on, sometimes while driving it would stay off, and other times it would stay illuminated, despite the belt being secured in the right place. Other times the light would turn on and off, irregularly, within the same drive. It is now stuck in the on position; the shoulder belt icon light is now always on whether the belt slider is parked in the open or closed position. The chime sound and glowing light on the dash while the belt is correctly stowed has gotten annoying. I am trying to correct the problem and silence both.

A few days ago, I took apart the control module under the parking brake/console and cleaned the contacts for the respective connectors, especially those for the automatic belts system. They were not corroded, but I cleaned them anyway. I also checked the seating of the two connectors that plug in at the seat belt motor. One connector comes from the slider end position switches of the two latch/parking mechanisms built into each end of the rail, and the other provides power to the motor from the battery. I took apart the closed-position latch for the slider and reassembled it. This seemed to have solved the problem, restoring the on/off function of the light, but only for the moment that I tested it with the interior all taken apart. After reattaching the rear seat and all of the interior panels and sealing everything back up, the light remained on again.

Does anyone understand the dash light feedback system for these shoulder belts? Where is the signal made that tells the dash light to illuminate or turn off. As far as I have learned, there are two position switches (very small tabs) that tell the system to stop the motor when the slider reaches the end of travel for both the open and closed positions. Is there an electrical loop within these that is synchronized with the closed position end that, upon contact/no contact, triggers the light? I suspect there is a lack of contact for the closed position somewhere. Is there a contact point or suspect component on these? Am I missing something?

Thank you all for your help.

 

Thank you for the link. There is a lot tied into this system, and it will be difficult to test every associated wire.

I took the seatbelt rail system apart and tested the switches at both (open/closed) positions, as well as the continuity of the circuits up to, and through, the junctions at the retractor motor. The switches do their job, the motor works, and those circuits seem to be working fine. The light stays on.

I think I will have to dive deep and take out the driver's seat and area carpeting to access the lines that run from the motor unit junctions to the PRCM box under the console. I suspect that there might be a faulty circuit in that section of wiring.

 

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It is not too terrible to remove the center console to access the control module. I did that, inspected, and cleaned everything up on the module/terminals. Thankfully, no drinks have been spilled on this one. I imagine that that somewhat precarious location is why such a robust case surrounds the PRCM circuit board. The terminals are still vulnerable, though, but not much corrosion was on mine.

I could take it all apart again and see if the wires running from the module to under the seat and out to the motor are in proper condition. At this point, I am unsure of the nature of the wiring routing from the door sill motor location to the control module under the console. Is there a ground location under the carpet that serves various wires? There has been some water in the driver footwell a long time ago from when the sunroof drains were plugged up and some prolonged rain overwhelmed them: flooded carpets. I wonder if there is wiring/ground damage somewhere in this unknown-to-me under carpet area that recently worsened to the point of failure. Just thinking out loud.

I imagine that there are not many of these cars on the road with the belt track system, let alone a working one. My car is ancient by current standards; I can see how my asking this question now is a bit surprising for you.

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I like your idea of taking apart a seatbelt buckle and learning its components. Interesting that you mention the possibility of an in-buckle switch there. The lap belt works correctly--no dash light issues there--but the shoulder belt . . . I don't see any wires that are attached to the mouse belt slider male end. The shoulder belt buckle (female) has no wires, either, but maybe there is still a magnetic switch within that buckle that eludes my understanding. How would such an in-buckle signal transmit? The only wired switches for the shoulder belt that I am aware of are the A and B position proximity ones that the motor seems to use when the belt is in either position. It would be interesting if there is indeed a magnetic handshake in the shoulder buckle that controls the telltale light on the dash.

Looks like I will be going to the salvage yard as soon as I can to take some shoulder belt buckles apart. Do you know if the plastic casing on the buckle is glued, or does it use slot/tabs to encase the mechanism? I've never opened one up and want to know if I'll need to bring something extra to cut open a glued/welded plastic buckle without destroying it. I will investigate the shoulder belt buckle situation before tampering with any carpeting in my car.

Thanks again for your help. Were you on the Saturnfans forum before the site went down? I feel very lucky that this one exists for help. I bet my question had already been answered in that massive repository of knowledge for these cars.

 

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I went to the salvage yard and got the shoulder buckles from the driver and passenger seats from an SL2 of the same year as mine. [That car was in immaculate condition; someone already took the whole front end/drivetrain, including front axles and knuckles, as well as the instrument cluster and driver's seat. The OEM exhaust system was still silver in color, as was the shielding. Car must've never been driven. Rear calipers and knuckles still silver colored. . . zero rust on anything. Wishing there were more parts left to take on that thing.]

The shoulder buckle designs are identical to those in my car, and the passenger and driver side buckles are also the same. I opened the plastic shell (pried at the seams) and was able to look inside. Looks purely mechanical on these cars, as far as buckle to slider connection is concerned. The internals of the mechanism are composed of a compact, yet robust, metal housing coated in plastic that has two springs to actuate the lock/release of the buckle via the orange button on the exterior. The entire housing is about 1.5" x 2". There is no room inside the housing for any sensing switches, reed type, or otherwise. Strictly, there is a slot for the mail end within the metal housing and the springs to actuate the release/hold mechanism. No wiring or unaccounted for space within the housing or on the mouse slider (as mentioned in a previous post).

I suspect that the mouse belts are somewhat of a nonspecific system, where the actual connection of the shoulder belt buckle to the slider isn't important, but rather the position of the slider itself being the case. I imagine that the A vs B position of the mouse signals via the microswitches to the SRCM under the console whether the light should come on or not. I tried both of the buckles I got from the yard and neither made any difference at the dash when the belt was in the closed, "B" position.

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Everyone knows that anything found on the internet is correct. Always.

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The mechanical switch described in your findings is indeed present in the lap belt buckle, but absent on the separate shoulder belt one. There is a wire that feeds from that lap belt buckle into the console, presumably to the SRCM. Somebody also took the driver seat from that car I mentioned above, including the lap belt switch mechanism. I wanted to investigate that while I was in there, but someone beat me to it. The passenger seat lap belt does not indicate open/closed with a dash light for these cars, so there is no switch or wiring for that one. I suspect the lap belts use the same type of microswitch as found in the mouse track system (A and B positions) and the closed position on the sunroof rail. (I recently rebuilt my broken sunroof rail componentry, and saw the same type of microswitch as found on the SRS track positions.)

Yeah, most of the switches on these cars seem to be electromechanical. No Hall effect switches on the belts. I took apart a microswitch (from a donor car closed "B" mouse belt track position) and there was a simple spring actuated open/close gate that closes/opens the circuit with the slightest touch from the little tab on the exterior of the microswitch.

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I find this interesting: the switches themselves are good, as I tested them for continuity, and the motor knows to shut off when the belt reaches position A and B. There is only one wire coming from position A and one from B going into the wiring junction at the motor. Several wires, of different color than those of the A and B switches, exit the seatbelt motor junction area and feed into the harness under the doorsill. I wonder if some of the A vs B position, open/closed, signal is used by the PRCM to light the dash or not. If so, maybe there is a fault along the way from the motor junction to the PRCM. I think I may have to check the condition of the wires running under the doorsill, seat, and carpet.

 

Thanks for the ideas and schematics. I was tied up for a while with some other things, and have been away from this project. That doesn't mean the light wasn't on, telling me my shoulder belt wasn't secured when it truly was. The track still works and the shoulder belt still retracts and extends with the mouse slider . . . and the light still remains.

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So yesterday I went to the salvage yard where they still had a car with automatic belts. I took out the center console and part of the seat cladding to access both seat belt modules, belt and shoulder, for the driver side. I closely inspected the module for the shoulder belt.

There are three main components within the retractor seatbelt housing that compose the unit: the rotatable spool of strap that constitutes the belt itself, an externally mounted tension spring that retracts the belt when there is no load against it, and an interesting switch that monitors only the status of the rolled up belt on the spool. This sensor is a proximity type, like the ones found elsewhere on the sunroof and mouse track A/B positions, and it indeed has a wire going to the PRCM. It is basically an on/off switch that is triggered according to the proximity of some movable unit that interacts with it. In this case, the switch is fixed inside the seatbelt frame/housing close to the spool of coiled belt. From this position, there is a small arm on the switch that lightly contacts the coiled belt material. As the coiler rolls up the belt, the diameter of the spooled belt increases, pushing against the small arm on the switch. At some threshold, the arm is pushed all the way against the switch, triggering the opening or closing of the circuit. (I don't know which status corresponds to which position of the little arm, as I did not take apart the switch--I kept it.) This signal is read by the PRCM.

It looks like what we have here with this shoulder belt signal is just an on/off scenario, as received by the seatbelt housing switch: is the coil of belt thick enough to close the switch, or not? If so, opened or closed is the signal back to the PRCM. It would still work with, or without, the presence of the coiler spring, provided that you rolled up the belt by hand to the suitable diameter. The spring pack of the coiler/retractor unit has no circuitry associated with it (I took it apart to see how it works).

This reads well into your hypothesis of the PRCM using both of the switch signals from the lap belt and shoulder belts to control the telltale lights on the dash. In light of this I actually wonder *if*, or how, data from the automatic belt slider system is used by the PRCM. I wouldn't be surprised if the actual shoulder belt mouse slider positions (A vs B) don't directly play into the light on the dashboard, but rather the effects felt at the belt spool switch, where the mouse slider pulls out seat belt from the coil (shortening the diameter of the coil) or allowing it to retract (increasing the diameter of the spool).


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I noticed that when I examined the driver side seatbelt spool/retractor assembly, there was no mechanism that stops the belt if you pull it forward very quickly. The only resistance is that spring, which is used to return the belt, rolling it up on the spool. That coiler is a simple mechanical unit that has no circuitry to report any kind of tension or travel. I tried the quick-pull test on the passenger seat of my car, as well as the driver one, and for both seats in the car at the salvage yard. There doesn't seem to be a lock built into them, at least not one that I could induce. Maybe there is no lock in the automatic shoulder belts, perhaps to protect the slider system, say, should someone engage the retractor lock and then open the door, triggering the mouse/slider to fight against said locked belt. Plausible, no?


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My next step is to check out that switch in the driver side shoulder belt retractor unit, so I will have to remove the center console completely this time, meaning I will have to pull off the shifter nob without my elbow smashing into the windshield (it can happen . . . ). I wonder if the switch is worn out or damaged, so I kept the one from the car in the salvage yard for this purpose. I really want to exhaust all possibilities before pulling up seats and carpeting.

 

Today I took off the console and accessed the driver side shoulder belt retractor unit. I removed the spool switch described in my previous post and tested it. There was no change in the circuit whether the arm was depressed or not. I tested the same piece I got from the salvage yard car and that one alternated closing and opening of the circuit via cycling of the switch. The one in my car was bad. I installed the other one and put everything back together. The dashboard telltale light is no longer illuminated while buckled in and driving. The culprit was that switch in the seat belt housing. Thanks so much for brain storming with me and leading me to investigate the sensing mechanism for these belts. Turns out that there are simple components, on/off switches, really, supplying information to the PRCM for the dash lights. Also, it looks like only the lap belts have a tension locking mechanism to keep the occupant secured in case of a sudden deceleration.

The switch in the driver side seatbelt housing closes the circuit when the belt is pulled out and buckled to the mouse track slider. When the belt is disconnected from the slider and allowed to retract back into the housing (spool), the switch opens the circuit to the PRCM.

 

When you think about it, it's just a dash light, a minor one, at that. Small, yet annoying, things like that still feel good to solve, though. It's nice to drive and see the dash in its normal state. Thanks again for your input.

I doubt that there are many cars like mine with working automatic belts still out there, but maybe someone can benefit from the information shared here.

I just noticed that the title of this thread reads SL2. Did I mistype that and never catch it until now? It must have been there the whole time. Not that it matters, but my car is an SC2.

 

Sorry to randomly chime in to this now but I was just wondering how you found parts to replace the auto seatbelts? Mine have just been locked in place and i use them manually lol