Estimates last updated October 16, 2025

2004 Mercury Grand Marquis Antitheft System Control Module Replacement Cost

The average cost for a 2004 Mercury Grand Marquis Antitheft System Control Module Replacement is between $408 and $436.

Labor costs are estimated between $61 and $90 while parts are typically priced around $347.
This range does not include taxes and fees, and does not factor in your unique location. Related repairs may also be needed.

Antitheft System Control Module Replacement

What is an Anti Theft System Control Module?

Anti Theft and theft deterrent systems have become more advanced over the recent decades. They have moved from Anti Theft devices bought from a store all the way to transponders in ignition keys or smart keys that must be present and accurate in order for the vehicle to start and run. This leap in technology has changed the required systems to computer based systems which require a dedicated computer (or control module) in order to facilitate the security of the vehicle. The anti theft system control module goes by many names according to the year, make, and model, but they all perform the same function - keeping your vehicle in your hands.

How does an Anti Theft System Control Module work?

Earlier systems used only a resistor in the ignition key. This resistor would intercept voltage from the anti theft control module, and return a modified voltage, signaling that it was the proper key. Now, transponders are used, and the Anti Theft module can actually read information from the key like an RFID tag. This information has to match the information in the anti theft control module exactly, and in some cases, the body control module will play a role in validating this information before sending the signal to the powertrain control module to start the engine. In all cases, the basic function of the anti theft control module is to disable the vehicle or sound the alarm when an improper key is used to access the vehicle or attempt to start the engine.

What are the symptoms of a bad Anti Theft System Control Module?

Everyone has heard a car honking wildly in a parking lot with all of the exterior lights flashing, and many people have tried to unlock their door or start their engine to find that their car has become that car. Besides the obnoxious honking and flashing lights, clicking relays will be heard inside the cabin of the vehicle, plus some sort of security light will illuminate of blink, and a message may appear on the instrument cluster to inform you of the security issue. Vehicles equipped with satellite connected alarms will be placed in contact with a representative from the service provider, and the engine may crank but not start, or do nothing. Luckily, the radio should function just fine, as well as other accessory systems.

Mercury Antitheft System Control Module Replacement Cost Estimates

The average cost for a Antitheft System Control Module Replacement is between $408 and $436 but can vary from car to car.

Mercury Grand Marquis

Mercury Grand Marquis Antitheft System Control Module Replacement Cost by Year

The average cost for a Mercury Grand Marquis Antitheft System Control Module Replacement is between $408 and $436 but can vary from car to car.

2011 Mercury Grand Marquis

$873-$902

2010 Mercury Grand Marquis

$873-$902

2009 Mercury Grand Marquis

$873-$902

2008 Mercury Grand Marquis

$462-$491

2004 Mercury Grand Marquis

$408-$436

2003 Mercury Grand Marquis

$408-$436

Antitheft System Control Module Replacement

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What is an Anti Theft System Control Module?

How does an Anti Theft System Control Module work?

What are the symptoms of a bad Anti Theft System Control Module?

Can I drive with a bad Anti Theft System Control Module?

If the anti theft control module has failed, the vehicle will need repair before it can be operated. If the vehicle returns to its normal state after several attempts to start or enter the vehicle, it is still recommended to bring the vehicle for diagnostics, as the problem will likely return. Note, no matter which part of the anti-theft system is defective, the result will immobilization unless the system recognizes the proper key.

How often do Anti Theft System Control Modules need replacement?

Anti Theft control module replacement is mostly due to physical damage, not internal failure. Many times these control modules are mounted under seats and consoles, so they are subject to being kicked, spilled on, and corrosion. The majority of failures from internal faults will be very new and very old vehicles, as a result of defects in workmanship or degradation over time.

How are Anti Theft System Control Module issues diagnosed?

This system is diagnosed with a computerized scan tool, which can read anti theft control module diagnostic trouble codes, check real-time and freeze frame data, and command the system remotely. Without the appropriate scan tool, some older systems can still be diagnosed by checking analog voltages throughout the Anti Theft system, but this method is limited to the expertise of the servicing technician. Factory software for Anti Theft systems is typically the most well-suited diagnostic solution, and even with this software, there is still a good amount of physical checks to be done. In general, the anti theft control module will be found faulty if correct inputs result in incorrect outputs.

How are Anti Theft System Control Modules replaced?

Replacing the anti theft control module will include removing interior body panels, trim, carpeting, or the instrument cluster in order to gain access. This may have already taken place during the diagnostic procedure for hands-on testing. If the anti theft control module is part of another unit, like the instrument cluster, for instance, the entire unit will need to be replaced. When the Anti Theft module is a stand-alone unit, it can be replaced by removing fasteners and electrical connections, installing the new unit, and reconnecting the electrical connections. Afterwards, the control module will require programming to match the data to the rest of the control modules in the vehicle.

RepairPal Recommendations for Anti Theft System Control Module issues

If you cannot get the alarm to shut off, we recommend disconnecting the battery until help arrives. This will prevent the battery from being drained by the many components activated by the anti theft control module, and allow the locksmith or roadside assistance personnel to better and more quickly assist you.

What to look out for when dealing with Anti Theft System Control Module issues

It is not recommended to attempt to bypass the factory alarm, as the anti theft control module is extremely difficult to "trick", and the repair may involve replacing one of many components of the anti theft system. This means that even if the bypass were to work properly, the failed component could still be part of the system, thus causing the security alert to continue.

Can I replace the Anti Theft System Control Module myself?

Anti Theft systems are extremely difficult to diagnose without factory software and years of experience. In nearly all situations, if an automotive locksmith cannot find the issue, it will need to be taken to a factory authorized repair facility for the make of the vehicle.