Does a Mileage Blocker Affect Your Car Warranty? (2026 UK Guide)

By Paul · Updated

Short answer: fitting a mileage blocker doesn’t automatically void your car’s warranty in the UK. But a manufacturer can refuse a claim if the module caused or contributed to the fault. And if your warranty has a mileage limit, using a blocker on the road to stay under it would be misrepresentation, which can void the warranty and could be fraud. Here’s what you need to know in 2026.

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Aftermarket parts and manufacturer warranties

Under UK competition rules, a car manufacturer can’t cancel your whole warranty just because you’ve fitted an aftermarket part or had the car serviced by an independent garage. What it can do is refuse a specific claim if it can show the aftermarket part caused or contributed to the fault.

A plug-and-play mileage blocker connects to the vehicle without cutting or soldering and can be unplugged at any time. Even so, it’s an aftermarket electronic module. If you had an electrical fault in the instrument cluster or the systems the blocker connects to, a dealer could question whether it played a part. Always check your own warranty terms, because they vary between manufacturers.

Warranties with mileage limits

Most new-car warranties run for a set number of years or miles, whichever comes first, for example 3 years or 60,000 miles. This is where honesty matters most:

  • A mileage blocker is designed for testing, diagnostics, track days and off-road use, not everyday road driving.
  • Using one on public roads to keep a car under its warranty mileage would misrepresent how far the car has travelled. Manufacturers can refuse claims on that basis, and it could amount to fraud.
  • If a car has covered distance that wasn’t recorded, be upfront about it with your dealer.

Extended warranties, finance and leases

Extended warranty policies, PCP and lease agreements are usually priced on mileage. Their terms typically require an accurate mileage, so don’t use a blocker on a financed or leased car to stay within an allowance. If you’re planning dyno or track use on a financed car, speak to your provider first.

How to protect your warranty

  1. Read your warranty terms for anything on aftermarket electronics and mileage.
  2. Use the blocker only for testing, track days and off-road use.
  3. Keep a simple log of when it was active and why.
  4. Tell the dealer it’s fitted when you book a service or make a claim.
  5. If a fault might be linked to the module, unplug it and contact us. We’ll help you work out whether it’s related.

The warranty on our mileage blockers

New Autotech UK mileage blockers come with a 12-month warranty, and our reconditioned modules come with a 6-month replacement warranty. Our blocker warranty and repair guide explains how to make a claim.

FAQs

Will a dealer know if a blocker has been fitted? Technicians can find the module when working behind the dashboard, which is one more reason to tell them it’s there. See Can Dealerships Detect Mileage Blockers?

Does removing the blocker restore the warranty? Your warranty isn’t cancelled by fitting one in the first place. What matters for a claim is whether the module caused the fault, and whether the car’s mileage has been represented accurately.

Is this legal advice? No. Warranty terms vary, so check yours or ask the manufacturer if you’re unsure.