Car Diagnostics Explained: Why A Car Diagnostic Check Matters
How to Navigate a Car Diagnostic Check
Maybe Vixa recommended one of our free diagnostic checks with a mechanic after sending a battery or engine health alert to your app.
Or perhaps you heard a funny noise while driving and came across the term as you searched for clues. Whatever the case, here’s what it actually means for you and your car.
What Are Car Diagnostics?
You might think of a vehicle as just metal and fuel, but modern cars house sophisticated electronics systems that are constantly gathering information.
Sensors and computer modules make up your vehicle’s onboard electronic systems to monitor its performance and detect faults.
A vehicle diagnostic test taps into this data to find out what's going on in your car when it’s not quite right.
Onboard systems track things like:
Engine performance
Fuel and emissions systems
Sensor readings
Electrical components
When something isn’t working as expected, the vehicle records a fault within its system. A mechanic can then run a diagnostic test on a car to see this stored information and diagnose the issue.
How Modern Car Diagnostics Work
Most vehicles built in the past two decades include onboard diagnostics (OBD).
In simple terms, OBDs work by:
Using sensors to monitor your car’s systems
Detecting when something goes outside normal limits
Recording this as a fault in your car's computer
Allowing technicians to access this data with a diagnostic scanner
Vehicle diagnostic tests often provide clues rather than definitive answers, but they give mechanics valuable insights as they inspect or repair an issue.
What a Car Diagnostic Check Includes
A typical automobile diagnostic test involves plugging a diagnostic scanner into the car to read its electronic systems, then reviewing the information stored by its onboard computers. This can include:
Reading stored fault codes
Reviewing system performance data
Checking emissions-related systems
Identifying irregular sensor readings
Depending on what appears during the scan, the technician might then carry out additional checks to pinpoint the cause. Diagnostics are often the first step in identifying an issue, not the repair itself.
Garage Diagnostics vs Ongoing Monitoring
A traditional auto diagnostic check is usually performed at a garage and gives a snapshot of the vehicle’s condition at that moment. But some tools and connected systems can monitor elements of vehicle data continuously.
Rather than performing a single scan, these tools observe vehicle health patterns over time. This can help you stay aware of developing issues when you’re between services or inspections.
Vixa is one of these tools, keeping an eye on your car’s health by monitoring key vehicle data over time to:
Track changes in vehicle performance
Highlight emerging issues early
Send prompts to investigate potential problems
Vixa doesn't replace professional diagnostic checks, but it supports proactive car care by keeping you in the know when it comes to your car’s health.
If you get an engine or battery health alert, Vixa shows you how to book a free diagnostic with one of our trusted AA garages, or get a Mobile Mechanic to come to you, to find out what’s going on.
When You Might Need a Car Diagnostic Check
For drivers who don’t have Vixa, it's common to only book a diagnostic test when something unusual happens, for example:
A dashboard warning light appears
The car loses power or runs roughly
Fuel efficiency suddenly drops
The vehicle struggles to start
A problem is suspected but not obvious
What Does a Diagnostic Check Cost?
The price of a car diagnostic check varies depending on the garage and the vehicle. But as a guide, most garages will charge somewhere between £30 and £100.
It varies because it can depend on the type of vehicle and the equipment required to run the check. You might also find that some workshops include diagnostics as part of a repair, while others charge a separate fee for the scan.
Why Car Diagnostics Matter
These checks make identifying faults more precise. Since modern vehicles rely so heavily on electronic systems, diagnostics give mechanics insights on your car that might not have been possible in the past.
A vehicle diagnostic test helps to show how the car’s systems are behaving and where potential issues may be developing. And for drivers, diagnostics provide clarity about what might be wrong and what steps to take next.
Understand how tools like Vixa help you keep track of your car.