Why is car alarm going off by itself?

Hi Carol , do you mean PATS passive antitheft system ? Locked up your car ,do you mean it won't crank over an start ?
The passive anti-theft system uses radio frequency identification technology to deter a driveaway theft. Passive means that it does not require any activity from the user.

• During each vehicle start sequence, the ignition key identification code is requested by the vehicle protection anti-theft electronics.
• If the key's ID code has been programmed into the system, the powertrain control module (PCM) (12A650) is signaled to enable the vehicle to start.
• If the key's ID code is not programmed into the system, or if no encoded key is detected, then the powertrain control module is signaled to disable the vehicle.

The passive anti-theft system communicates the state of the security system to the powertrain control module via the J-1850 communications network data link connector (DLC). The powertrain control modulebased on the communications from the passive anti-theft system, will determine if the vehicle's engine is enabled to start. The passive anti-theft system differs from the active anti-theft alarm system in that the passive anti-theft system enables/disables the vehicle from starting and only operates with the ignition switch in RUN/START position. The active anti-theft alarm system has perimeter protection capabilities and operates only with the ignition switch OFF. Refer to Section 13-11A for active anti-theft alarm system information.
Vehicle Disabling The passive anti-theft system will be activated and disable the vehicle from starting if any of the following conditions exist:

• damaged encoded key
• unprogrammed key
• non-encoded key (key has no electronics)
• wiring concern
• transceiver concern
• Passive Anti-Theft System (PATS) control module concern
• J-1850 Communications Network concern
• Powertrain Control Module (PCM)

the remote key would be the easiest (and cheapest) thing to try first but i don't think that a low battery in the fob would activate the alarm randomly , i'd get the OBD codes read as will point to which part of the anti theft/central locking system is causing the issue

Anti-Theft - Perimeter The anti-theft perimeter protection feature is controlled by the front electronic module (FEM), the rear electronic module (REM), and the driver door module (DDM). The alarm can be armed using:

• the LOCK button in the remote keyless entry (RKE) transmitter to the DDM, which sends a message through the standard corporate protocol (SCP) communications network to the FEM.
• the driver or passenger door lock switch if the corresponding door is open when LOCK is actuated.
• the key in the driver door lock cylinder.
• the RKE keypad by pressing 7/8 and 9/0 simultaneously.

The FEM and REM then monitor all features, which activate the alarm in the event of an unauthorized entry.
The luggage compartment lid lock cylinder does not disarm the vehicle's perimeter alarm. The luggage compartment alarm can be temporarily inhibited through the luggage compartment lid disarm switch, located in the luggage compartment lock cylinder or by opening the lugguage compartment with the RKE transmitter or the RKE keypad. Once the luggage compartment lid closes, the perimeter alarm system immediately starts monitoring the luggage compartment. The perimeter alarm can only be disarmed:

• by unlocking the vehicle using the RKE transmitter.
• by unlocking the vehicle using the driver door lock cylinder switch.
• by cycling to RUN a valid programmed key in the ignition switch.
• by entering the correct vehicle unlock code on the RKE keypad.

Additionally, an ignition switch tamper circuit and a signal hardwire line from the FEM to the REM are monitored.
If any of the above features receive any activation once the alarm is armed, the alarm activates the visual and audible alerts. ......

Are you setting your car alarm? a flashing light that says theft on it is normally an alarm system that is activated when you lock your doors, if this is comming on during driving it can be due to the alarm system being disabled or other wise having problems.

Hi Edward:
In dashboard, your THEFT warning light is blinking? If the answer is yes, your antotheft system is activated and will need restart and resynchonized. This occurs when battery is disconneting or other un-authorized key is used.

Vehicles equipped with Vehicle Theft Security System (VTSS) are protected from vehicle theft andunauthorized entry. VTSS system monitors vehicle doors, hood, liftgate and ignition. If an attempt is made toenter or operate vehicle without proper disarming of system, vehicle horn will sound, headlights, taillights andparking lights will flash, and engine will be prevented from running.

VTSS system arms when ignition is off, vehicle is exited, door is locked using power door locks and door isclosed. Alternatively a remote keyless entry transmitter can be used to arm system. A security light on panelwill flash for 15 seconds to indicate system is arming. At the end of 15 seconds, if no door, hood or tailgate isopened, system is armed.

If alarm is triggered, horn will sound for 3 minutes, and lights will flash for an additional 15 minutes. If hornsounds 3 times when either front door is unlocked, vehicle has been tampered with (tamper alert). If doors arelocked manually or with key, system will not arm (manual override). If an unauthorized entry does occur, VTSSsystem signals Powertrain Control Module (PCM) to prevent vehicle from being driven. PCM reduces injectorpulse width to zero, causing a start and stall condition.

System can be disarmed with the keyless entry transmitter, or by using key to enter vehicle. In both instances, if alarm was activated, vehicle alarm will be terminated. If battery is disconnected and reconnected, alarm will beactivated and it will be necessary to disarm system as indicated.

Please, send us some email account to send you this procedure in PDF format file.

The security alarm system on the 1994 Jeep Cherokee arms itself on any normal exit from the vehicle, i.e. ignition off, open door, lock door with power door locks, close door. If the doors are locked with the key, it does not arm.
If the battery is disconnected, then reconnected, the alarm system will go into powerup alarm mode. The lights will flash, but the horn will not blow.
The alarms can be disarmed by a keyless vehicle remote or by unlocking either of the front doors or the read lift gate with the key. If the key method does not work with any of those three entrances, there is a problem either with the input to the alarm module or the module itself.
There is a switch in both front doors and the tailgate which is activated by manualy unlocking those doors. The alarms can be disabled by permanently grounding the wire going from either of those switches to the alarm module, but this will remove all theft protection.
The best thing to do is to find out why the system is going off in the first place. It could just be a glitch, a loose connection that can be fixed fairly easily and keep your theft protection intact.

Glenn

If this is an after market alarm, an alarm that was installed by someone other than a dealer there will be an in-line fuse under hood on the main power wire leading to the alarm horn. Usually along the firewall. Remove this fuse and you should be able to start the vehicle. The problem you are experiencing is the anti theft or ignition kill switch being activated because the alarm is detecting the lose of power as a Surge and triggering the anti theft circuit.

Put the key in the driver door lock (or the trunk lock if you don't trust the driver's door- quite often on a vehicle of this age the wires break in the door and it won't electrically de-activate the alarm due to the broken wires)
Disconnect the battery.
Turn the key to the unlock position (toward the front of the car if using the driver or passenger doors) and release it- it will go back to centered, but will retain slack in the forward direction
Then reconnect the battery. You may get one beep out of the alarm horn. If it beeps continually, turn the key to unlock again.
As long as the alarm is de-activated it will not prevent the car from starting. If you are still having a problem it is not alarm related.

Good luck and keep me posted, be glad to help

Section 13-11: Anti-Theft System, Active 1998 Windstar Workshop Manual DESCRIPTION AND OPERATION Anti-Theft Alarm System NOTE: The system immediately monitors the ignition key lock cylinder upon removal of the key from the ignition. It is not necessary to arm the system for ignition key lock monitoring.

The anti-theft alarm system:

• protects the vehicle from unauthorized entry into the passenger compartment, engine compartment and cargo area.
• monitors the status of the ignition key lock cylinder.
• is controlled by a remote anti-theft personality (RAP) module. The remote anti-theft personality module also controls the electronic door lock functions. Refer to Section 01-14B for more details.
• when armed, detects unauthorized entry into the passenger compartment by using an input from the GEM module regarding the state of the door or liftgate (open or closed).
• protects the engine compartment with a hood switch which is located on the LH cowl vent panel and is part of windshield wiper motor wiring (17A477) .
• triggers an alarm if the ignition lock cylinder is forcibly removed from the steering column.

Once triggered, the system responds by:

• flashing the low beam headlamps, the parklamps, rear lamps and the alarm indicator warning light emitting diode (LED).
• sounding the horn (13832).
• disabling the starter circuit until the system is disarmed.

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Remote Anti-Theft Personality Module

• The remote anti-theft personality module is located behind the instrument panel (04320).
• It contains a radio receiver that receives the RF signal from the keyless entry remote transmitter (15K601) through the alarm and lock system antenna (15603) and sends the appropriate command to the power door locks, the horn relay, or the generic electronic module.
• The remote anti-theft personality module is equipped with an internal backup power supply which holds the programmed code in memory in the event the vehicle battery is disconnected.

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Remote Anti-Theft Personality Module Removal

1. Disconnect battery ground cable (14301). Refer to Section 14-01 .
   

1. Remove radio. Refer to Section 15-01 .
   

1. Remove lower instrument panel center finish panel. Refer to Section 01-12 .
   

1. Lower glove box.
   

1. Remove two remote anti-theft personality module bracket retaining screws.
   

1. Disconnect electrical connectors and alarm and lock system antenna (15603).
   

1. Remove remote anti-theft personality module and bracket.
   

1. Remove remote anti-theft personality module from mounting bracket.
   

Installation

1. To install, follow removal procedure in reverse order.
   

1. Tighten remote anti-theft personality module bracket retaining screws to 6-8 Nm (54-70 lb-in).
   
   

Components The system is composed of the following components:

• remote anti-theft personality (RAP) module with integral antenna
• alarm indicator LED
• door lock cylinder switch RH, door lock cylinder switch LH
• liftgate door lock cylinder switch (220A40)
• hood switch (part of windshield wiper motor wiring (17A477))
• ignition lock anti-theft switch (19A438)

The following vehicle components are also used by the anti-theft alarm system:

• generic electronic module
• power door lock switch (14028)
• door open warning lamp switch (14018)
• autolamp relay (14N089)
• horn relay and bracket (13853) and horn (13832)
• low beam headlamps
• rear lamps (13404) and parking lamps (13200)
• starter relay
• door lock relays
• keyless entry remote transmitter (15K601)

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Disarming an Untriggered System NOTE: A perimeter alarm will "shut off" after 165 seconds, but the system is still triggered and is not disarmed.

An armed but untriggered perimeter anti-theft system can be disarmed by one of the following four events:

1. Unlock the doors by pressing the keyless entry remote transmitter (15K601) UNLOCK button once.
2. Unlock any door with a key.
3. Turn ignition switch to RUN or ACC.
4. The remote entry PANIC button will disarm the anti-theft system only when the perimeter alarm is triggered and sounding.

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System Triggering NOTE: Although the remote entry PANIC alarm is not associated with the monitoring of the vehicle, the user will frequently say that the theft system was triggered when actually the keyless entry remote transmitter PANIC button was inadvertently pressed. A panic alarm will not flash the THEFT indicator.

The alarm can be triggered by the following events if the system has been armed and has not been disarmed first:

• Open any door or liftgate.
• Open the hood (16612) (if the hood was open when the system was armed, it must be closed before it can trigger the alarm).
• Dislodge the ignition key lock cylinder.
• The anti-theft system may be triggered inadvertently when the module is disconnected and then reconnected. To avoid inadvertent alarm triggering, disconnect the smaller 22-way connector first.

When the system is triggered the perimeter alarm will operate as follows: The remote anti-theft personality module will pulse the following outputs at approximately 1.3 Hz, 50 percent duty cycle for two minutes 45 seconds for North America. NOTE: Other perimeter alarms can be programmed for the system.

• low beam headlamps
• parking lamps
• horn
• THEFT indicator

The perimeter alarm can be retriggered, after a perimeter alarm has sounded for 165 seconds. After a perimeter alarm has timed out, if any trigger input is first seen as normal and is then seen in its trigger state, the perimeter alarm will be retriggered. The perimeter alarm can be triggered a total of three times between an arming sequence and a disarm event. An active panic alarm will be deactivated when a perimeter alarm is triggered (a perimeter alarm overrides a panic alarm).

If you use your keyfob to lock the doors, it will activate the alarm, and you will need to unlock with the keyfob. If you lock the doors with the lock button on the inside of the door, it should not activate the alarm.