Buying and selling a used car
What should you do if a warning light comes on soon after buying a used car?
Read the fault before clearing anything and write down the code, the freeze frame data and the status of the readiness monitors: they show when the fault appeared and whether the codes were cleared shortly before the sale. Keep that scan with its date and talk to a shop; if you bought from a dealer, find out what warranty applies to you.
Reviewed by Daniel Morales, founder of Reprorace SL, on
What do I do first?
Look at the color of the light: if it is red or the check engine light is flashing, stop and call for assistance. If it is yellow and the car drives normally, you can carry on carefully until you read it.
Read the code and the freeze frame data (speed, temperature and mileage at the moment of the fault) and do not clear it: it is your evidence of when it appeared.
How do I know if the fault was already there?
If the readiness monitors are still incomplete or the counters since the last clear show only a few miles, the codes were probably cleared shortly before the sale.
A permanent code, on cars that keep them, also suggests the fault predates the sale. None of these is conclusive on its own, but they help piece together what happened.
What should I keep?
The dated scan, screenshots or a shop report, the listing, the contract and your messages with the seller.
If the shop makes a repair, ask for an invoice with the written diagnosis.
Who do I turn to?
If you bought from a dealer, the sale usually comes with a legal warranty or protections: contact the seller in writing as soon as possible. If you bought from a private seller, different rules apply depending on where you live.
This page is not legal advice: to make a claim, talk to a consumer protection agency or a lawyer.
General guidance only: every manufacturer and model has its own details. Always follow your vehicle's manual and, if in doubt, ask a workshop.
Related
Related trouble codes
- P0420Catalyst system (bank 1): efficiency below threshold
- P0171Mixture too lean (bank 1)
- P0300Random or multiple cylinder misfire detected
- P0128Coolant thermostat: coolant temperature below the thermostat regulating temperature
Related symptoms
- Engine warning light on and steady: what it means and what to do
- Flashing engine warning light: what it means and what to do
Learn more
See what your car is saying
With the ECO-LITE you read the code, the freeze frame and the monitors in your account, and your shop can review them remotely with your permission; the scan is saved with its date.
Presale price: €129 · US$129
Frequently asked questions
Can I clear the code to see if it comes back?
Better not until you have written it down and, if you plan to make a claim, until a shop has seen it: clearing loses the freeze frame data.
Could the light be for something minor?
Yes, sometimes it is a loose gas cap or a sensor. The code tells you.
How long do I have to make a claim?
It depends on where you live and whether the seller was a dealer or a private seller. Act quickly and in writing.