Interlock installations fail for many of the same reasons. The charging system does not support the device, the wrong relay tap was selected, the device was not properly calibrated and the client was not informed of how a rolling retest works. All of these scenarios will result in a lockout, a violation report and/or a warranty dispute that can take so much more time to resolve than the actual installation.
But most of this risk can be eliminated prior to the install taking place by getting the vehicle assessment, wiring, commissioning tests and subsequent service visits right the first time.
Assessing the vehicle before you commit to a slot
Treat the pre-installation inspection process with the respect it deserves, as it serves as a ‘gate’ to the interlock installation process. Most interlocks consume power continuously, and will present failures on older vehicles suffering from “parasitic drain” problems that are incorrectly blamed on the interlock.
Check these items before the vehicle is booked in.
- Battery condition and resting voltage, plus alternator output under load. Anything below roughly 12.4 volts at rest warrants a battery replacement conversation first.
- Existing aftermarket alarms, remote starters, or previously removed interlocks, which often leave spliced or taped harnesses behind the dash.
- Push-button start or keyless systems, which require a different install approach than a conventional key barrel.
- Hybrid and electric drivetrains, where the starter circuit does not exist in the conventional sense and the manufacturer’s approved method must be followed exactly.
- Fleet telematics or CAN-based accessories already fitted, since two devices sharing a data line can produce intermittent faults.
Documenting the condition on arrival
Take photographs of the dashboard, steering column, and trim sections including the instrument binnacle, photograph the odometer and note any pre-existing damage. These photos can be used as evidence against any claims made post installation for damage to trim panels etc. They will also act as a reference point when removing the interlock from the vehicle years later.
Wiring, mounting, and the choices that determine reliability
Care must be taken to position the ignition interlock within easy reach of the driver, and to ensure it does not obscure the view of the road or interfere with airbag deployment. The route of cabling through trim panels, etc. Is also crucial, and must avoid pedal boxes, seat rails and other obstructions. Sufficient slack must be left in the cable so that the ignition interlock can be pulled down to the mouth and allow for the rolling retest technique to be used.
From a vehicle perspective, there are 4 main requirements for any Ignition Interlock to function, switched ignition, constant power, ground and starter inhibit. All of these should be connected to existing wiring within the vehicle and where possible the wiring should be tapped into at existing connectors as detailed within the vehicle wiring diagram. The use of T-taps and scotch locks can be detrimental and is not considered an acceptable method to connect wiring within an installation. Manufacturers may supply approved harnesses that plug directly into the devices. When selecting a provider for the professional car breathalyzer installation of an Interlock it is wise to check what wiring standards they work to as opposed to what devices they supply. Drivers who want that standard met without hunting for it should start with a shop that specializes in car breathalyzer installation in Virginia and can show its harness practices on request.
Starter inhibit versus alternative immobilization
Interlock installations into vehicles can require the starter solenoid trigger wire to be cut and connected to the interlock. In some complex vehicles however the solenoid trigger wire is routed via the Body Control Module (BCM) and interrupting this wire can create a fault code with the vehicle. In such cases alternative wiring methods can be employed such as connecting to the fuel pump relay or by the use of an OEM approved Immobilizer Interface.
Commissioning tests before the vehicle leaves
A device that simply powers up does not constitute having been tested for full functional sequence.
- Confirm the handset wakes on ignition and completes its warm-up within the specified time.
- Perform a zero-alcohol sample and verify a pass result is logged with the correct timestamp.
- Attempt a start without providing a sample and confirm the engine does not crank.
- Trigger a rolling retest and observe the prompt, the grace period, and the alert behavior on a missed test.
- Verify data upload or logging, then check the recorded event trail matches what was performed.
- Confirm no dash warning lights, no lost radio presets, and normal operation of any stop-start system.
Client handover
Explain all the different aspects of the driver displacement alcohol interlock such as sample collection, retesting periods and missed service dates. Let the client provide a sample and explain what happens during a lockout. Leave a copy of written and verbal instructions in the vehicle for future reference, along with the emergency contact number for the device.
Service intervals and what each visit covers
| Activity | Typical interval | Purpose |
| Data download and review | 30 to 60 days | Compliance reporting to the monitoring authority |
| Sensor calibration | Every 6 months or per manufacturer | Maintains accuracy of the fuel cell |
| Harness and mounting inspection | Each service visit | Detects tampering, chafing, and corrosion |
| Firmware update | As released | Fixes known faults and rule changes |
| Removal and reinstatement | End of program | Restores factory wiring and closes the record |
Missed appointments and tamper flags
Set reminders in the booking system for 14 days and 3 days before the missed service to inform and remind the client and mechanic of the impending lockout. Record all instances of tamper, including loss of power and case-open events, with corresponding notes from the technician. Unexplained tamper flags will be much easier to defend with a dated note from the day the flag was recorded as opposed to months later.
