Why Perform a Car Diagnostic


– Intro

– Definition of road worthiness test

– Why should you have your vehicle diagnosed?

– Definition of the car pre-test diagnosis

– What services are available for the pre-test diagnosis?

– Tools used to make a diagnosis

– Who are the service providers for the pre-test diagnosis?

– Car diagnosis: a highly variable cost


All cars, with the exception of some collector cars, must undergo regular technical inspections under strict regulations.

If the date of validity of the technical inspection is exceeded, the owner can be fined for failure to undergo a recent technical inspection.

It is therefore important to prepare your vehicle for this test. And for this, a car diagnosis is necessary.

Definition of road worthiness test

The roadworthiness test is a comprehensive periodic examination regulated by the Highway Code. It allows you to check the running and maintenance condition of your vehicle by a complete analysis of its main components.

Why should you have your vehicle diagnosed?

Before the technical inspection, it can be interesting to carry out a pre-test diagnosis of the car in order to audit the general condition of your vehicle. If it can prove to be expensive and risky depending on the service provider, it generally allows you to avoid going through the counter-visit.

Definition of the car pre-test diagnosis

The pre-test diagnosis is a preliminary examination aimed at preparing vehicles for the mandatory road worthiness test, thus avoiding a repeat inspection.

What services are available for the pre-test diagnosis?

Mike Jones, 31st Force Support Squadron Auto Hobby Shop manager, uses a lift to elevate a sport utility vehicle Aug. 18 at Aviano Air Base, Italy. Jones uses the vehicle lift to have better access to the under carriage. (U.S. Air Force photo/Airman LaVel Sterling)

The pre-inspection diagnosis covers the main points of the technical inspection. There are 133 of them, spread over all the organs and functions. There are more than 600 points of failure. The failure points are divided into 3 levels: minor, major and critical failures.

Major and critical failures lead to a counter-visit. In case of a critical failure, the vehicle is no longer allowed to circulate except on the day of the inspection.

Please note: the anti-pollution test carried out during the technical inspection is reinforced on vehicles running on diesel. During this test, the quantity of particles emitted from the exhaust pipe is compared with the quantity specified by the manufacturer. If the approval values are exceeded, the vehicle is subjected to a counter inspection.

Tools used to make a diagnosis

The tools needed for diagnosis are the same as those used by the technical control centres:

– Diagnostic device;

– Exhaust gas analyzer;

– Reguloscope (headlamp adjusters);

– Geometry measuring bench (front and rear axle inspection);

– Brake and shock absorber measuring bench.

Good to know: very few workshops are equipped with shock absorber measuring benches and the checks are visual, accompanied by the removal of the wheels and rear brake drums, if the vehicle is equipped with them.

Who are the service providers for the pre-test diagnosis?

All automotive professionals offer a pre-control diagnosis:

– Independent workshops (garages of all makes): many provide this service and, at your request, present the car themselves for the compulsory technical inspection.

– Brand agents and dealerships: this type of establishment provides you with the expertise of professionals, especially if your vehicle belongs to the network’s brand.  Here too, the inspection is carried out by the workshop and your vehicle is returned to you after the approved technical inspection.

– Car centers: the vehicle is taken care of from diagnosis to the technical inspection.

Car diagnosis: a very variable cost

In general, the services offered are free of charge. The workshops are paid for any work required to bring the car back to conformity, after an estimate has been drawn up.

Good to know: some states require the operators of technical control centers to send the Ministry of Economy and Finance the price of their services concerning light vehicles. The prices will eventually be freely accessible to the public who will be able to compare them.

Advantages: the pre-inspection is free of charge and relieves you in theory of the formalities for the technical inspection and a possible counter-inspection. This formula allows you to have complete control over your personal planning, avoiding repeated and unforeseen vehicle downtime in the event of a counter-visit.

Disadvantages: pre-diagnosis with visit at the technical inspection is an expensive solution when including the eventual repair costs. The professionals being under the obligation of results, will not take risks and will often opt for the preventive replacement of parts, thus inflating the invoice.

Some possible overcharging: rear brakes ($180), front brakes ($250), tires (from $100 to $400 for 2 tires), etc.

There are also risks of abuse:

– Some workshops botch or forget certain check points, which leads to a refusal at the technical control. Obviously, the time lost and the cost of the counter-visit, even if it does not appear on the invoice, will be indirectly charged and will inflate the invoice.

– Some unscrupulous professionals may give in to the temptation to inflate the repair estimate, going so far as to carry out repairs that would not have posed a problem for the technical inspection. In the worst case, the promised diagnosis is completely disregarded and repairs are made only after the counter-visit.

So, if you are looking for professional auto maintenance and repair shop, Xtreme Motor Works is the place to go. You can trust their 14 years of experience in the automotive industry.

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