It is generally accepted that the most electrical problems are with the battery. This is true, but the main function of the battery is to start the engine, and then it is actually inactive, and the entire load of providing the car with electricity falls on the generator. Despite its reliability, this unit is also susceptible to damage, and in the event of a failure, you will have to rely only on the battery. It's good if it's new and charged. If this is not the case, your car will turn from movable property to real estate.
The best way to avoid trouble is to prevent it. In our case, the first sign that something is wrong with the generator is a loosening of the drive belt tension. The problem is that this nuisance often happens gradually, unnoticed. And yet there is a very clear symptom that indicates a problem: the appearance of a characteristic squeal from under the hood, which is initially initiated only when the accelerator pedal is pressed sharply. A squeal indicates that the belt began to slip at high speeds, most likely due to its sagging. If you do not take any measures, soon unpleasant sounds will be heard in all operating modes of the power unit. However, the same sounds can come from a weakened power steering belt, and the timing belt is a sinner of this.
It's easy to identify the culprit. Stop the engine, open the hood and use your fingers to apply pressure to the drive belt. If the level of deflection exceeds 5 mm, it needs tightening. The second sign of a weakening of the alternator belt is a decrease in the battery charge level under the same conditions (for example, with the same mileage at the same speed). But this factor harder to notice.
The model has different configurations, generations, assemblies, so the selection of a belt can really become a problem. Fortunately, there is an online service like service.citroen.com where you can find out which belt fits your SKU, as well as belts for other trim levels.
True, first you need to register, but not as a private trader, but as a professional repairman. Otherwise, you will not be able to use the service.
After logging in with your identification data in the upper left corner of the page, enter the VIN code of your C4 and select the section to search for spare parts.
Having found the belt, we copy its article, and with this number we go to exist.ru. And already here you will be shown all suitable belts for your car. However, information on exist is not always complete and sometimes incorrect. But this is why the Internet and the automotive community exist, so that in case of doubt, ask a question and get an answer to it. Perhaps more than one, and it is not even excluded that these tips will contradict each other.
As for the specific size of the alternator belt for Citroen C4, then for restyled modifications produced from 2015 to our time, this is 90.6 cm.