Adapted from KanNZ, with AA guidance checked on 11 October 2026.
If you realise you have put petrol into a diesel car, or diesel into a petrol car, stop filling. Keep the ignition off. AA warns that turning the key can activate an electric fuel pump and circulate the wrong fuel even before the engine starts.
If the engine is still off
- Stop using the pump and leave the ignition off.
- Tell the service-station staff what happened. Explain where the car is and ask how to keep the area safe while help is arranged.
- Contact roadside assistance or a qualified repairer. Describe the vehicle, the fuel it requires, what you added and approximately how much.
- Follow their instructions. Do not attempt to dilute the mistake by adding more of the correct fuel and driving away.
Keep the receipt or take a note of the pump and product you used. Giving the repairer a clear account is easier than trying to reconstruct it later. If you are unsure which fuel the car needs, check the filler flap and vehicle manual.
If you have already started or driven
A petrol car filled with diesel may struggle to start, run unevenly or lose power. Petrol in a diesel system can interfere with the lubrication its pump and injectors need; modern common-rail systems can be particularly vulnerable.
If the car is running badly, move to safety only as necessary to stop safely, switch off and contact assistance. Tell the responder that the engine has run, rather than describing the problem as a mistake discovered at the pump. The repairer needs to assess the system before advising whether draining alone is enough.
A rental car needs an extra call
Tell the rental company as well as roadside assistance, and ask who should authorise recovery and repair. Keep records of the instructions. Do not assume a roadside membership or insurance policy pays for every part of a misfuelling incident.
AA’s Rental Care terms describe fuel extraction where available or towing to a suitable repairer or safe place, at the driver’s expense. Your own rental agreement and cover may differ.
Fuel grade and fuel type are different questions
Using 91 instead of 95 petrol is a different situation from mixing petrol and diesel. Check the manufacturer’s fuel requirement and seek advice for the specific car rather than assuming every wrong grade has the same consequence.
At truck stops, read the product name carefully. AA also warns about Diesel Exhaust Fluid, often called AdBlue: it belongs in its own dedicated tank, not the diesel fuel tank. Pump position or colour alone is a poor way to identify a product.
Before the next fill
Pause at the filler flap, read the required fuel and then read the pump label. This is especially useful in a borrowed or newly rented car. Save your assistance provider’s number before a trip so you can find it without searching beside a pump.
