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]
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:
1. Between computer and blue 4-pin connector on the B pillar [under floor carpet];
2. Between blue 4-pin connector and limit switches [along the belt track]
3. 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
0
Figure 7. The B pillar covers removed
Figure 8.Top to bottom: 4 pin connector, door courtecy 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 G]
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”]
Troubleshooting the automatic seat belt control circuit
Linear Mode
