How much does it cost for a vehicle diagnostics test?

By Julia Freeman

Modern cars have a wide range of electronic monitoring systems on board to keep an eye on the engine, transmission, brakes and numerous other areas of the car. Apart from a couple of dashboard lights these are largely invisible to the driver, but they can be interrogated by mechanics to help identify if anything is wrong with a vehicle. Usually they save a great deal of time which would otherwise be spent looking for a fault one component at a time.


What is a car diagnostic test?

Special equipment is needed to interrogate on-board computers. Cheap ones don’t do much more than interpret dashboard error codes but Protyre’s qualified fitters use equipment capable of reporting sophisticated performance details and even service histories. These tests can report on the engine, transmission, exhaust, ignition coils, throttle, oil tank, fuel injectors, coolants, airflow and most other systems. A diagnostic can reveal developing faults as well as any that are already a problem.

How much does it cost for a diagnostic test?

Across the UK, garages usually charge between £50-£100, but it can vary according to the quality of their diagnostic equipment and the sophistication of the car model. Luxury cars, high performance sports cars and unusual vehicles are sometimes asked to pay substantially more - usually because the tests take longer. Protyre conduct thorough examinations but charge at the low end of that range.

What should I do if my check engine light appears?

Fans of “The Big Bang Theory” will know that Penny's check-engine-light was an ever-present feature of her car, but do you know what to do if the dreaded light appears on your own dashboard?
Unfortunately, in many cars the check engine light can be triggered by many different problems. The first thing you should do is to check the rest of your dashboard lights and gauges. If your oil pressure is low or your engine is overheating you should pull over and stop the engine immediately. In other cases, you may not notice any obvious differences when driving with the check engine light on, but your performance may be decreased, or fuel consumption increased.
Generally speaking, if your check engine light is steady it indicates that your car needs to be serviced or inspected soon. If the light is blinking however, you should get your vehicle to a garage as soon as possible. Remember that the longer you drive with a fault present in your vehicle, the worse it is likely to get, which generally equates to a higher repair bill.

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How long does a car diagnostic test take?

Most full diagnostic tests can take between an hour and 90 minutes to complete. Occasionally issues are uncovered that make things more complicated, or your vehicle may have components that have to be removed before a diagnostic test can be performed, in which case the time can increase to between two and three hours. This does not include the time required to fix any issues which are discovered.

What does a vehicle diagnostic test tell you?

A diagnostic test can reveal all kinds of problems that could be manifesting in many parts of your car. Modern cars have one or several on-board computers linked to all manner of sensors throughout the car. They monitor the engine, transmission, exhaust gases, steering and countless other systems. Fault codes are stored by the computer in order to help make diagnosis of a problem quick and easy but more data is available with the right equipment.
Few consumers have much idea what the fault codes really mean but Protyre mechanics are trained to interpret them. They are also experienced in the common faults that affect different models of car. When the fault code provides insufficient information, they can quickly access additional details to confirm their diagnosis. The process is much faster than tracing a fault by mechanically dismantling the vehicle.

Diagnostic trouble codes

Fortunately, most diagnostic trouble codes have been standardised and are known as “OBD-II” (On-Board-Diagnostics) trouble codes. These codes are generated when a fault is detected or whenever a system is not working within acceptable limits, and then stored within the car's memory.
Each OBD trouble code is formatted in a similar manner, allowing for easy diagnosis of faults. There are well over 200 fault codes that can be generated by a vehicle but they fall into the following four main areas;
Those with a B prefix are “Body” codes, covering things inside the passenger compartment such as driver assistance, airbags, air-conditioning and general passenger comfort and safety.
Chassis Codes begin with a C and refer to most of the mechanical systems including the suspension, braking and steering.
Powertrain Codes start with a P and refer to engine components, transmission and other associated drivetrain parts.
U codes are concerned with the vehicle network and wiring and other vehicle Integration systems, including the computers and sensors themselves.

The local garage you can trust

If you have any worries about the condition of your car, you can book a free vehicle check, or a full electronic diagnostic at your local Protyre garage using either our online booking system or contact forms. In addition to vehicle examinations and tyre safety checks from our tyre professionals, Protyre also stock a great range of tyres, including premium tyres from Pirelli and Bridgestone. With many same-day appointments available, our easy to use tyre guide will help you find the right tyres for your vehicle.

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About the author

Article Author Photo
By Julia Freeman
Julia is Head of Retail Marketing for Protyre and loves engaging with customers and the business as a whole to make sure Protyre is more than just a local garage.
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