SRS - Troubleshooting Advice
88saab01FILE IN S.I. Man VOL. I
SEC. A-3 PG. 108
Service Information
SUBJECT: SUPPLEMENTAL TROUBLESHOOTING ADVICE ISSUE: 01/88-1027
APPLICATION: 900 MODELS WITH PASSIVE BELT SYSTEM
Avoid "Shotgun Diagnosis" when making repairs. A sound understanding of the basics of electricity, coupled with proper diagnostic procedures, will enable the technician to determine the repair. Use the guidelines given here and in the Saab supplied Service Manual (3:2, M1987-88) and the Passive Restraint System Training Manual.
FIGURE 1 - SPECIAL LOCKING TONGUE INSTALLED AT THE "B" PILLAR.:
Owner Advice
If a malfunction occurs in the Passive Belt System, an emergency locking device may be used to allow the affected shoulder belt(s) to be utilized by the occupant. A special locking tongue (two tongues, one left and one right, stored in trunk tool kit, Figure 1), is attached at the "B" pillar which enables the occupant to manually fasten the shoulder belt. The separate lap belt should also be fastened, as usual.
FIGURE 1 - SPECIAL LOCKING TONGUE INSTALLED AT THE "B" PILLAR.:
FIGURE 2 - CONNECTING SHOULDER BELT TO THE SPECIAL LOCKING TONGUE.:
Show the customer how to use the emergency locking tongue (Figure 1 and 2). If one shoulder belt is inoperative the locking tongue should be used for that belt and the other one can work
automatically. If an intermittent fault is occurring which cannot be immediately corrected, the system should be deactivated while the emergency locking tongues are being used. Deactivate it until repairs are made by removing the fuses under the rear seat.
Troubleshooting
Function Check - Operate the system and evaluate the complaint. Interview the owner or operator thoroughly to understand the exact nature of the complaint.
Battery - The battery must be fully charged before beginning diagnosis. A discharged or low battery (9-10 volts or lower) may not operate the belts.
A dead battery complaint can be caused by a wiring fault (bad or no ground) or a fault that causes the transport mechanism drive motor to run continuously. The transport motor should shut off when the mechanism reaches the "A" or "B" pillar. Don't overlook the possibility of a current draw elsewhere in the vehicle.
NOTE
Do not make any wiring modifications to the system.
System Integrity - Restore all of the vehicle's wiring to its original state before beginning your diagnosis. This means to disconnect any dealer-added aftermarket or unapproved accessories that may be connected to the door switches or any other part of the wiring harness affecting the Passive Belt System.
FIGURE 3 - GROUND LOCATION. NINE WIRES ATTACHED TO TWO RING TERMINALS.:
Inspect the system ground (Figure 3) beneath the rear seat. There are nine black ground wires secured with a single sheet metal screw at the cross member.
The screw must be tight. If it is not, replace the sheet metal screw with a 6 mm nut and bolt and tighten securely. Reconnect any ground wires that may have been disconnected during other repairs.
Wiring Faults - Check the wiring connectors and plugs for pushed-out or loose terminals. Improper operation of the belts (the wrong side moving for example) may indicate crossed wires. The wires connecting the right and left side belt reels to the control unit have the same color wires. The left and right transport mechanisms have the same color wires also. Trace carefully.
Electronic Control Unit (ECU) - A nonfunctioning system may be attributed to water damage at the ECU. Check for evidence of water damage and replace if necessary. Cars built from October 1987 production (date code on ECU 870921) gave an ECU that is more resistant to moisture entry.
FIGURE 4 - ALWAYS TEST WIRE CIRCUITS FROM THE BACK OF THE ECU PLUG.:
Seat Belt Reels (or retractors) - The reels contain a microswitch and solenoid which allow the belt reel to turn freely during certain conditions. The solenoid acts on the belt reel and the microswitch signals the ECU as to the solenoid position. These are key signals and both must be checked. See the Service Manual 3:2 or the Saab Passive Restraint System Training Manual for checking the reel. The seat belt reel may be checked with a digital volt-ohmmeter (VOM) at the back of the plug for the ECU (Figure 4). Some expanded testing advice is given here.
When testing the reel with the ECU unplugged, pin 21 (driver's side) should become grounded when pins 25 and 8 are jumped. Pin 17 (passenger's side) should become grounded, when pins 25 and 4 are jumped. When a ground occurs this indicates that the solenoid and the microswitch in the seat belt reels are working properly. If ground signals are not received, inspect electrical
connections. If a problem is traced to a seat belt reel, the reel must be replaced. A reel cannot be repaired.
Transport Mechanism - The mechanism is driven by a motor that moves the upper part of the shoulder belt between the "A" pillar and the "B" pillar. Limit switches at each position signal the ECU when the shoulder belt is at the "A" or "B" pillar. Switch failure can cause the transport motor to run continuously, even if the ignition is off.
FIGURE 5 - ALWAYS TEST WIRE CIRCUITS FROM THE BACK OF THE ECU PLUG.:
Always check the "A" and "B" pillar limit switches as part of your diagnostic routine. Test the switches with a digital VOM at the back of the plug (disconnected) for the ECU (Figure 5). Both "A" pillar switches should be open with the driver's and passenger's belt at the "A" pillar. The switches must be closed when the belts are at the "B" pillars. The same is true for the "B" pillar limit switches. They should be open with the transport mechanism at the "B" pillar and closed at the "A" pillar. The limit switches are located in the motor assembly. They are not repairable. In the case of a defect the motor assembly must be replaced.