What Causes Ignition Interlock Problems in a Car?

by Ronald Kimmons
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An ignition interlock system sometimes is placed on an automobile after someone has been convicted of a DUI charge. Similar to "breathalyzer" devices carried by police, ignition interlock systems are meant to serve as a deterrent of repeated offenses. However, as these systems require intricate installation, they occasionally cause automotive problems.

How It Works

Before the driver of a vehicle outfitted with an ignition interlock system can activate the ignition, he or she must breathe into the device. The system will test the driver's blood-alcohol content (BAC) for an illegal level. If an illegal BAC is found, the vehicle will not start, and some systems also have an alarm that will be activated if the driver's BAC is too high. In addition to testing before ignition, these systems also require tests at random times.

False Readings

Some people with ignition interlock systems installed in their vehicles trigger them without drinking any alcoholic beverages. This is because some products, such as mouthwash and cough syrup, have recognizable alcohol levels. The system will react to such alcoholic content exactly as it would for liquor, beer or wine. Also, according to Lawrence Taylor's DUI Blog, even dieting can cause the system to give false readings.


According to the New Brunswick Department of Public Safety, cold climates can cause built-up moisture in the system mouthpiece to freeze and keep the vehicle from starting. Also, some drivers experience malfunctions while they are filling up at gas stations because the gasoline fumes register the same as alcohol would. Most systems are built to deal with this, though; they will automatically warn you before you try to take a reading, giving you the opportunity to let the fumes dissipate before continuing with the reading.

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