What is A Vehicle Diagnostic Test?
It is a process that identifies malfunctions and issues in a vehicle’s onboard components. This test uses an OBD (Onboard Diagnostics) system that continuously monitors the performance and current condition of several vital components, such as transmission, engine, brakes, exhaust and more. When the system detects a potential fault, it notifies the owner by creating an error code that can be read using a diagnostic tool.
A vehicle diagnostic test generally checks the following system
- Brakes and ABS
- Exhaust and emissions systems
- Engine performance
- Electrical systems
- Airbags and safety systems
- Transmission
What is an OBD System?
All modern vehicles come with an in-built diagnostic system comprised of the vehicle’s onboard computer. It monitors several of the vehicle’s mechanical and electrical systems. OBD systems generally are of two types, i.e.:
OBD-I: It is an obsolete system that was found in vehicles manufactured before 1996. This was a first-generation system that used manufacturer-specific error codes, meaning every maker used their own specific set of codes.
OBD-II: The vehicles manufactured after 1996 used a standardised system that came with a universal connector and standard set of error codes, making it easier for the technician to diagnose problems.
How Does A Vehicle Diagnostic Test Work?
There is a simple process to conduct a vehicle diagnostic test. It is comprised of the following 4 steps:
- OBD Port Connection: A diagnostic tool is connected to the vehicle’s onboard computer using the OBD port. This port is generally located under the vehicle’s dashboard.
- Data Retrieval: The diagnostic tool retrieves the DTCs (Diagnostic Trouble Codes) that are stored in the onboard computers. These codes provide pinpoint information about the issues.
- Analysis: The retrieved error codes are then interpreted by the software that provides the precise location of the problematic system, such as sensors, engine or emissions.
- Repairs: This information is used by the mechanics to diagnose problems, execute repairs and eliminate any error codes.
What are Diagnostic Trouble Codes (DTCs)
Diagnostic trouble codes, or DTCs, are a set of alphanumeric codes that provide the precise location of the problem. These codes are generated by the OBD system whenever the corresponding issues are detected.
These codes are categorised into 4 categories, i.e.:
P-codes (Powertrain): Related to the transmission emissions systems and engine
C-codes (Chassis): Related to systems like traction control, ABS, and suspension.
B-codes (Body): Related to seat belts, airbags, and other interior systems.
U-codes (Network): Indicating communication issues between different vehicle modules.
What are the Diagnostic Tools?
The tools that are used to read a vehicle’s error codes during a vehicle diagnostic test are known as diagnostic tools. There are different diagnostic tools that are currently being used to read the DTCs, such as:
Basic OBD-II Code Readers
These are basic tools that can easily read the DTCs and clear them. These tools are relatively inexpensive and display basic information about the issues.
Advanced Scan Tools
These are advanced tools that come with several features and provide live data from several systems. They also offer advanced diagnostic functions that are relatively expensive.
Manufacturer-Specific Tools
There are some tools that are manufactured specifically for some car brands, such as Toyota, Ford, BMW, etc. These tools provide a deeper diagnostic opportunity and can also access proprietary systems.
Most Commonly Detected Issues in a Diagnostic Test
Vehicle Diagnostic tests can detect a vast range of problems, including the following:
Engine Issues: Fuel system problems, misfires, ignition system faults
Emission Problems: Catalytic converter issues, faulty oxygen sensors
Transmission Issues: Solenoid problems, slipping gears
Electrical Problems: Alternator or battery issues, faulty sensors
Brake and ABS Issues: Malfunctioning ABS sensors and brake fluid pressure problems.
Airbag and Safety System Faults: Faulty airbag sensors and seat belt pretensioner issues.
Why A Vehicle Diagnostic Test is Important?
There are several benefits that highlight the importance of a vehicle diagnostic test. These benefits include the following:
Preventative Maintenance: It Identifies potential issues at an early stage and allows us to rectify the problem before it becomes a major one.
Improved Fuel Efficiency: When the issues of a faulty oxygen sensor are cleared, it can improve the overall fuel efficiency of the vehicle.
Emissions Compliance: Diagnostic tests also help you ensure that your vehicle’s emissions are well within the environmental limits.
Cost Savings: Detecting the problems at early stages can save you money in the longer run in terms of costly repairs.
Enhanced Safety: It increases the reliability of the safety systems by identifying the issues with airbags, brakes, and other safety systems.
What is the Cost of a Diagnostic Test?
The cost of a diagnostic test depends on several factors, such as:
- Where the test is being performed?
- What is the make and model of the vehicle?
- How deep is the diagnostic going to be?
However, in the UK, the cost of a vehicle diagnostic test generally ranges between £50 to £150. Although it seems expensive, vehicle diagnostic tests can prove to be cost-effective and save you from expensive repairs.
How Frequently Should You Do the Diagnostic Test?
There are no clear guidelines on the frequency of the diagnostic test. However, most technicians recommend executing a thorough diagnostic test during your annual car inspection. You should also get your car diagnosed whenever you feel any change in the performance of your vehicle.
