Volkswagen Front Wheel Drive 1974-1989 Repair Guide

Central Locking System

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TESTING



See Figure 1

The heart of the pneumatic central locking system is the bi-pressure pump mounted in the luggage compartment. The pump runs both ways to provide vacuum or pressure as required for locking or unlocking. There are lock actuators at each door, the rear hatch or trunk and at the fuel filler door. The master actuator at the driver's door includes the switch that activates the pump. In normal operation, the pump runs for about 2 seconds and will build enough pressure or vacuum to operate all locks and activate an internal shut-off switch. If the pump runs for more than 5 seconds, a leak in the system is preventing shut-off switch operation and an automatic shut-off will occur in about 35 seconds. If the pump does not run at all, the problem is most likely electrical.

  1. Open the luggage compartment and remove the left side interior trim. Unhook the strap, remove the pump cover and pull the pump out of the housing.
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  3. Install a small clamp on the hose before the first branching tee and turn the key in the driver's door lock. If the pump does not run at all, go to Step 7.
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  5. If the pump runs for more than 5 seconds, the shut-off switch inside is faulty and the pump must be replaced. If the pump stops in less than 5 seconds, the pump is good and there is a leak somewhere in the system.
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  7. Move the clamp to the upper branch of the tee and turn the driver's door lock again. If the pump runs too long, the leak is at the left rear door actuator or the hose.
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Click image to see an enlarged view

Fig. Fig. 1: Central locking system schematic

  1. If the pump stops in less than 5 seconds, move the clamp to the next hose junction at the right rear of the luggage compartment and test again. The hose that branches to the right supplies the fuel filler door and trunk or hatch actuator. The hose branching down supplies the right door actuators.
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  3. Continue moving the clamp towards the actuators until the pump does not stop within 5 seconds. This means the clamp is now past the leak and the previous section of hose or actuator is leaking.
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  5. If the pump does not run at all, disconnect the wiring and connect a voltmeter or test light to the center and right terminals on the connector. There should be 12 volts when the driver's door is unlocked.
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  7. Move the tester to the center and left terminals. There should be 12 volts when the driver's door is locked.
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  9. If the voltages appear as specified, the pump is faulty and must be replaced. If there is no voltage in either or both tests, the lock switch, wiring or fuse is faulty. The switch is part of the master actuator and cannot be replaced separately.
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REMOVAL & INSTALLATION



See Figures 2 and 3

  1. To replace the pump, remove the left luggage compartment interior panel and remove the pump cover and the pump. Test the new pump before completing the installation.
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Click image to see an enlarged view

Fig. Fig. 2: Master actuator in the driver's door



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Fig. Fig. 3: Unlatch the cover to remove the pump

  1. To replace the actuator, remove the door panel. Follow the hose to the actuator and disconnect the hose and the linkage at the actuator. On the driver's door, disconnect the wiring.
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  3. Remove the screws and remove the actuator. Connect the hose to the new actuator and test the system before installing it.
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