Hi, welcome to Just Answer.
Try unlocking the driver's door twice with the ignition key, this will disarm the system. However, if you have a weak or defective battery, it can cause the alarm to remain armed. If the battery is questionable, I would remove it and have it tested at a local repair shop or auto partsa store. Let me know if your still having trouble disarming it.
Sounds like the alarm system may have a deeper fault. Try removing the battery cable, turn the ignition key on and than reinstall the cable with the key on, see if that disarms it. If not, I have a great deal of infomration on testing the alarm system and even bypassing it...but it requires automotive electrical experience in order to repair this system. Let me know if you would like me to post it.
No problem, if you decide to do the electrical testing let me know. If not, take it to a reputable VW shop that are experienced in these. Below is some really handy information on this alarm system....if you take it in you may end up spending close to $250 for a diagnosis and repair.
MKIII Central Lock / Alarm Help. - BEEEP BEEEEP BEEEEP BEEEEP
What is it? - Its your factory alarm in your MKIII Golf or Jetta. All US cars came with a central locking system and a factory perimeter alarm.
And for the the most part, it works fine. Arming itself when you lock the car with a key fob or key in the door. Un-arming itself when you unlock a door. The factory central lock system uses a vacuum pump system (in the trunk, or rear of the car..) and makes a "moan" when its running. On Jetta/Vento cars the lock pump is on the drivers side. On Golf cars the pump is located on the passenger side.
When the drivers door is "locked" all doors will also lock. Red LED on drivers door will flash. Car will "arm" with all doors, hood, and trunk closed (and latched down).
One turn from the drivers door to unlock the car opens the drivers door, and cancels the alarm. Two turns to unlock opens all doors.
If a trunk, hood, or door is opened the alarm will go off, the lights (on later cars) will flash, the alarm will go off, and the the starter will be disabled.
The only way to disarm the system is to press unlock on the factory remote, or unlock the drivers door with a key. Putting the key in the ignition will not cancel an alarm.
Inserting a key into the drivers (or passenger door) lock cylinder and turning and *holding* the key in the lock position will arm the system and then close all windows and the then sunroof. (note, power windows and/or electric sunroof only).
Unlocking the car the same way will - one unlock opens drivers door (mechanically), and turns off alarm. Two turns will unlock ALL doors - and if its "held" in the unlock position - will open all power windows (note, the sunroof will not open)
The factory system only disables the starter. If the car cranks - the alarm is not at fault. The US MKIII system does not have a "Immobilizer" like the MKIV models do. There is NO "chip" in the key.
But problems arise and things go wrong. The alarm "goes" off at all hours of the night, or worse it prevents the car from starting! But lets look at some key facts..
Note: This page does *not* cover the Cabrio immobilizer system found on MK3.5 (1999.5-2002) cars.
The MKIII model line, as said earlier were all equipped with factory door central lock systems. However, there are a few odd ball cars out there, and of course, alarm systems changed from year to year... but here goes:
1993-1995 - Central Lock System w/Alarm. System as drivers and passenger door lock cylinders. To lock all doors in the car, the drivers door pin is the "central lock switch" and all other door pins follow suit. Alarm module is Silver. These cars also have a locking fuel door as part of the central lock system. The car must be "unlocked" to gain access to the fuel filler. This added feature may be added to later cars by adding and tapping into the central lock vaccum system and getting an older style fuel door lock.
1996-1997 - Same as above, but added a central lock switch button in center console. Also added flashing lights to arm/disarm/alarm (parking lights). Alarm module is Black.
1998-1999.5 - Same as above, but added *factory keyless*, removed passenger side door lock cylinder. Remotes are Banjo shaped, and Alarm module is White. - Deleted passenger side door lock cylinder. If the car is "disarmed" or "unlocked" AND it does NOT see a door, trunk, or hood open in 30 seconds, it will re-arm itself.
Shown above, the factory remote, if your remote does NOT look like the one above, your car does NOT have a factory keyless system, and this DIY may not fully apply..
Can I add factory keyless? - Yes (external link)
Can I add an aftermarket system? - Yes follow this link.
How do I get to the alarm horn?
How do I program a remote?
Replacing the battery.
Close Ups Of Modules, and inside them
System Component Locations
How do I get to the module?
Bypassing the alarm module - but still getting the car to start.
Behind the fuse box
Taking off a door panel (rear) w/manual windows (external link)
Taking off a rear door panel (rear) w/power windows (external link)
Typical Problems and solutions;
Door is locked, and LED flashing showing alarm was armed.
But at some point (30 seconds to hours later) the alarm goes off.
The alarm module intermittently lost power. Unplug alarm module and reset the two plugs. Check the wires into the fuse block to make sure they are all seated. Check connectors "D, H, and Y"
Other possible defect, low (main car) battery voltage or bad battery cables. The alarm will sense the drop in voltage and go off, thinking the car is begin stolen.
Alarm is going off, and the car will not crank to start.
Alarm is able to be bypassed, however, 1998 and later cars will loose keyless lock/unlock. Pins T/5 and T/6 MUST be jumped to start car. (see below).
Door is locked from the outside, LED does comes on, but flashes slowly. No alarm honk is heard.
Check for broken wires in the body or damaged alarm switches
Door is locked from the outside, LED does not come on, and does and does not flash. No alarm honk is heard.
Missing alarm system module, or loss of ground, or power to module.
Lights flash and alarm horn sounds - its flat out scary the first time it happens, and its pretty embarrassing.
Once the door is opened the alarm goes off.
If alarm module has power/ground and batteries are new, and all remotes will not program - replace alarm module.
Programming new remote controls
Two keys and all the remote controls that are to be programmed will be needed. The maximum number of remote controls that can be programmed, including old and new, is four.
For second remote control, press button -1-, two beeps will be emitted. Use same procedure to program third or fourth remote control. All remote controls must be programmed within one minute, otherwise new programming will cancel and old remote control programming will be valid.
Replacing remote battery
• Insert screwdriver into slot at side of button 3 (Trunk rear/lid button) and lift upper part off (observe polarity).
VW Part number: N103 221 01 = battery
Close up of modules:
many thanks to Bob D (a3clusters (at) hotmail.com) for the following beautiful pics..
Note: Later cars (1998 and later) and all VR6 cars have the hood latch as part of the hood-alarm switch.
#1 shows the vacuum pump air line#2 shows the door latch micro switch#3 shows the door pin lock rod
the module is orientated like this inside the car.. while sitting in the driver seat.
To gain access to the alarm module:
remove headlight switch;
remove lower cover off fuse box (2 or 3 screws) pull down cover.
remove lower knee bolster cover (under steering column) again, 2-3 screws
unclip and lower down fuse block.
Now you can unbolt the one bolt that holds the alarm module to its bracket.. and then reach up under the dash to grab it and gain access to the alarms wires and plugs.
Bypassing the Alarm
A view of the module from inside the headlight switch.
The Alarm plugs. The 6 pin connector is on the right.
The 6 pin alarm plug close up - note the two heavy gauge wires that are used to power the starter. These are the two wires that need to be "jumped" if you are bypassing the alarm module if you ever want your car to start again.
NOTE: With the alarm bypassed/unhooked - Central lock system will STILL work, HOWEVER, if you have FACTORY keyless (white box), your keyless functions will be LOST!
Rear of fuse panel: Check connectors "D, H, and Y"
Alarm schematic (general Golf/Jetta all years)
Door Pin Switch / Door Switches
(Note rubber boot) remove door pin switches with a small screwdriver. They CAN be taken apart and blown out with air, and then packed with silicone grease. But its critical the the rubber boot be in place. The rubber boot comes with the switch. It cannot be ordered separately.