Troubleshooting the automatic seat belt control circuit


In order to determine when to fasten or retract the automatic shoulder belt, the computer needs input from belt track limit switches and door position switch.
Each belt uses 2 control circuits in order for motor to move the belt, one of these signal circuit should be connected to the ground; if neither one is connected, the belt will not move. I will describe driver’s side circuit, as passenger is similar.
As I mentioned in my previous work [1], it is easy to understand how these switches are working if we imagine the belt anchor [the actuator of limit switches] to be located somewhere in the middle of its travel. In this position both limit switches are having continuity which means only the position of the door tells the computer, which direction the belt should run; so computer is changing polarity at the motor accordingly.
When door is closed the belt will move toward the driver.
When the door opens up, the belt will change direction and move toward the windshield.
The stages of belt movement shown at Figures 1 to 6:
Fastening [after door is closed]






Releasing [after door is open]





Figures1 to 6
At the end of its travel the anchor will hit the limit switch actuator, and push it in, interrupting the circuit and stopping the motor.
If door will be closed at this time, the switch in the latch will ground another circuit with rear limit switch which has continuity and the belt will again run toward the driver, until it hits the actuator of the rear limit switch.

The computer provides following functions:

• The belts will move toward the windshield when door open, even with ignition off to allow occupant to get in the car;
• The belt will keep running even if key is switched off until the anchor hits limit switch.

Note: the EWD page (Figure14) shows incorrect type of door latch switch, as there are only TWO positions in it; it always connects to the ground either one out of two wires, depending if door is open or closed.
The signal circuit is the first suspect to check if one of the belts is not moving or it moves only in one direction, after manually resetting it with thumbwheel.

The wiring of signal circuit can be subdivided into three sections:

• Between computer and blue 4-pin connector on the B pillar [under floor carpet];
• Between blue 4-pin connector and limit switches [along the belt track]
• Between blue 4-pin connector and door switch

Therefore the blue 4 pin connector makes excellent starting point for continuity checking.
[Figures 7 to 9].

To begin, remove the B pillar inner trim and expose 4-pin connector


Figure 7. The B pillar covers removed


Figure 8.Top to bottom: limit switch connector, open door switch connector, belt motor connector


Figure 9.This blue connector makes a good starting point for continuity check

First step: check section 3


There should be continuity:

• Between the pink wire terminal and the ground with door open;
• Between the pink/green wire terminal and the ground with the door closed

If no continuity in both cases check the ground wire between the door harness connector and door latch switch ground terminal; using Figures from 10 to 12 for reference

Figure10 Door harness connector left kick panel [connector E]

Figure11 Door latch s/w connector; note the changing wiring color; replacing that switch require door latch removal.

Figure12 Door latch switch; closing the door pushes actuator in; black is common [ground wire]

Second step: check the limit switch circuit, section 2:


The wires leading to the limit switches are coming to the upper part of 4-pin connector, which is attached to B pillar. For testing, refer to Figure13.

Figure 13 Limit switches


With motor disconnected, move the belt about 2 inches from its end point using thumbwheel; in this position the continuity should be present:

• Between two white wires [front limit switch];
• Between two black wires [rear limit switch];

With belt at front-end stop, there should be NO continuity between wires leading to the front limit switch;
With belt at rear-end stop, there should be NO continuity between wires leading to the rear limit switch

Finally check the section 1:

• Get access to the computer; this can be done by unsnapping the cover under parking brake handle
• Unplug connector from computer
• The green and green/red wires from lower part of the blue 4-pin connector on the B pillar are leading to the 18 and 16 computer connector terminals respectively [Figure 14]; there must be continuity from end to end of each wire. Careless replacement of the carpet causes these wires to be damaged near terminal Q, similar to the one described in [1].

Figure 14. Wire colors and terminal numbers. Note: the automatic shoulder belt switches N and O are on/on type not on/off/on as shown on the diagram! I added the red line to show correct switch position [doors closed, belts fastened; rear limit switches are “open”]
Reference: [1] http://www.toyotanation.com/forum/t172839.html

 

Thanks for the awesome detailed post with photos. Man, I've been running back and forth referring to this for hours.

I've two Camrys. Loved them both and both are pushing 300k. Great cars. I hate to see them wearing out.

Anyway, I've had the seatbelt problem three times. Two on the drivers side and one on the passenger.

The first was a short in the wiring boot between the door and front left kickpanel. A little saudering and it was good as new, and lasted a couple years.

The send time I went through all the gymnastics of testing out the door wiring and limit switches, etc. to make sure there was continuity and the switches were working, but but never found the problem.

Three days later, the passenger side went out. So far, no luck at all. I'm starting to think it might be the retracter motor itself on the passenger side.

Q: i'm curious if anyone has had that little "motor" go out and how hard it is to replace. The lazy alternative would be to move the seat belt back by hand, seal it all up and leave it. You still have a seatbelt, you just have to manually move it across into position.

My hope however is to find the real culprit and repair it, so it's done right.

Thanks again for yur post. The photos were a huge help.

 

I realize this is an old post. I have recently come across this problem on my 91 Camry DLX 4-door for the first time. Any chance of having these pictures reposted? Thanks.

 

No, the internet may have something.

What is the problem?

 

My driver-side automatic seat belt is stuck in the "out" position. That is, it pulled forward when I opened my door, but it did not retract/return back towards me. I hear two clicks from the center of the dash board (Door Control Module?) as soon as I close my door.

I have accessed the thumbwheel in the pillar that allowed me to bring the belt back (with the motor disconnected). As soon as I reconnect the motor and turn the key, the seat belt goes out again and stays there.

 

The belt system uses a computer to operate. The above posts no longer having photos describe various switches, etc.

It could be the drivers seat belt switch is not working. The computer reacting to what would be the seat belt still on.

There could also be a break in a wire going between the drivers door and chassis.

 

I encountered this challenge a few years ago with my 90' Camry, which I sold about 6 months ago. But, I still have a 91 Camry DX.

Using the method described above, I was able to repair the problem temporarily, doing the same things you're noting above... using the thumb ear to retract it, checking for shorts in the system, etc. Slow process that requires some patience.

As noted, is seems like you "might" have a short in the wire on the relay system, that tells the system to apply or retract the seat belt. Or possibly a faulty relay.

In the end, I put the seat belt in the "on" position and disconnected the motor on that door. That way, you just sit down in the drivers seat, and the belt is on. It wasn't a real issue, and, for me, I determined that it wasn't worth the hours tracking through it all again. It did the job just fine for 4+ years, until we sold the car.

It's totally a judgment call.

If you're determined, you fully understand the electrical aspects and want it fixed no matter what. You can get it done.

I'm guessing when you shut the door, the little motor whirs for a few seconds as it "attempts" to bring the belt around. If so, it might also be something in the motor or the cable or track system that needs replaced. Replacing the motor is probably the easiest piece of it... it's the track and relays that I found challenging. (Keep in mind, I'm just a weekend knuckle buster. Not a pro.)

Good news is, the wrecking yards offer tons of this stuff at a ridiculously low price. It's just determining what the problem is.

You might be fortunate and find a short or broken wire connection and be able to simply fix that. That would be very nice and relatively easy.

I'll watch to see how your progress transpires, as I still have and drive regularly the 91 Camry -- and might run into this again. Gen 2 Camrys are great cars, I'm approaching 250,000 miles and going strong, 30+ mpg, and it's great in the snow. God has been oh so gracious.

And, if you find posts from Doctor J, go with it, he's a Camry rock star. Other good source on many topics is EricTheCarGuy videos, often on YouTube.

 

Thanks for the info, thefranks5. I went to my local auto electric repair shop (yes, they specialize in all things electrical), and for $40, they were able to determine that all the components are functional, and the problem is wire/connection related. I saw them (from a distance) connect something that allowed the seat belt to move forwards and back.

When closing the door, there is no whirring noise from the motor. Just two clicks the come from behind the center of the dash (door control module?).

As you did, I simply had them disconnect the motor so the belt remains in the "closed" position. Being the kind of person I am (by no means a pro), I'm certain that if I could see the pictures originally posted here, I could manage to find it. (Like you, on the weekend, of course.)

Thanks again!

 

If the electrical shop found the problem and fixed it, why did you disconnect it. I'm guessing that was a separate previous occasion, and it went out a second time, right?

Glad that provided an interim fix for you.

Also glad that manufacturers no longer make automatic seat belts, yikes, what a maintenance nightmare.

 

Hello. I have read and copied the Dr. J thread about this issue. I have a 91 camry that has sat for 4 years. It has developed seat belt issues in that time. It has much more serious issue, which is in process of being dealt with by mehanics. My seat belts are stuck in the open position. After the front brakes/dragging issue is dealt with, I want to drive it home to my place, a 500 mile drive; currently at my Sister,s in the Vancouver, WA area. Long story on the situation of it sitting/neglected for 4 years, but... everything was working when it got parked.
So, I would like to just get the belts to the closed position for this journey, and then I will work with getting the belts to work properly Unfortunately, the Dr. J article photos have disappeared (age?). Can I just get to that thumb wheel deal that moves it back to closed position, and I'm still unclear how to access that.
Thanks in advance for any guidance.