1. Ask, and read the paperwork
Ask the seller straight out whether the engine computer was ever reflashed. Receipts from a tuning shop or for tuning software are the clearest sign there is (Voytech Tuning). A tuning device left in the glovebox is another.
2. Read the software ID and fingerprint
An engine computer can report the name of its program (the CAL ID) and a code calculated from that program (the CVN). Change the program and the CVN changes (California BAR). Cars built for the US since 2005 have to report the CVN (CARB); cars built for other markets may not. Compare the CVN with what other cars on the same CAL ID report and you can see whether this car runs the same program.
That’s what our check does with a Bluetooth OBD adapter and a browser. It has two blind spots: a car flashed back to stock reports the factory code again, and some tools make changed software report the factory code (a “CVN fix”).
3. See when the codes were last cleared
Clearing fault codes also restarts the car’s emissions self-tests and resets counters for warm-ups and distance since the clear. A seller who cleared codes the day before you came may be hiding a warning light. Permanent codes survive the clear until the car’s own test passes, so look at those too. Our check shows all of this next to the software result.
4. Ask a dealer
Carmakers’ own tools see more than any OBD adapter. Dodge says a reflash leaves a permanent mark even after the car goes back to stock (Motor Biscuit), and Audi owners report dealers flagging unauthorised software with a warranty code called TD1 (Audizine forum). It costs a diagnostic fee, but it’s the check that matters for warranty: Dodge refused a $36,000 engine repair on a 790-mile Hellcat over non-factory software (Autoblog).
5. Pay a tuning shop to read the whole program
A shop with tuning tools can read the full program and compare it with the factory file. That shows exactly which maps were changed. It’s the most thorough option and the slowest, because the car has to go to the shop.
What doesn’t tell you much
- How the car feels on a test drive. A mild tune can feel stock.
- A basic code reader that only shows fault codes. A tune doesn’t have to set one.
- Aftermarket parts on their own. They hint at a tune but don’t prove one.
Can you check a remap by the number plate?
We know of no public record of remaps by registration number. Plate checks show a car’s registration history, not the software in its engine computer, so the software has to be read from the car itself: by you with an adapter, by a dealer, or by a tuning shop. To do it yourself, check if the car is tuned with a Bluetooth OBD adapter and a browser.
Why it matters
Beyond warranty, undeclared tuning can cost you your insurance: a UK insurer voided a policy after a crash over an undeclared remap, and the Financial Ombudsman agreed (Financial Ombudsman). In California, a car whose software doesn’t match the factory or an approved version fails smog (what to do).