Here's what you should do to find the correct information:
1. Consult your owner's manual: The most accurate and reliable information about timing belt replacement intervals is found in your vehicle's owner's manual. It will specify the recommended mileage or time interval for your specific Synergie model and year.
2. Check with a Citroën dealer or a qualified mechanic: If you don't have the owner's manual or are unsure about the interval, contact a Citroën dealer or a trusted mechanic specializing in Citroën vehicles. They have access to service schedules and can give you specific advice tailored to your car.
Important notes:
* Neglecting to replace a timing belt on time can result in catastrophic engine damage.
* Timing belts are wear-and-tear components, and even if your manual states a higher mileage or time interval, it's generally a good idea to err on the side of caution and replace it sooner rather than later.
* If you are unsure about the condition of your timing belt, it's best to have it inspected by a professional.
Remember, neglecting this essential maintenance can lead to costly repairs.