If your car’s check engine light comes on, your car starts idling, or something just does not feel right with your car, a car diagnostic test is usually the way to get real answers without guessing about your car.
A modern vehicle is packed with sensors and control modules that constantly monitor how your car’s engine, transmission, brakes, airbags, and other systems are working. When something goes wrong with your car, your car often stores a fault code and related data. A diagnostic test is how a technician pulls that information about your car and turns it into a direction for what to inspect and fix in your car.
Continue reading to learn more about what a car diagnostic test can tell you about your car, what it cannot tell you about your car, and how to use the results to make repair decisions about your car.
What Are Car Diagnostics?
A car diagnostic test is a scan of your vehicle’s on-board systems. It uses a tool or specialized computer to communicate with your car’s internal computers, read error codes, and review sensor readings in your car.
Most cars today use On-Board Diagnostics standards, which started evolving in the 1970s and became widely standardized as OBD2 in recent years. In vehicles like your car, the OBD2 port is usually located beneath the dashboard near the steering column or around the driver’s area.
When a scanner connects to that port in your car, it can retrieve:
- Diagnostic Trouble Codes about your car
- Live sensor data from your car
- Freeze frame data from your car
- System readiness monitors from your car
A Diagnostic Test VS A Full Diagnostic Test
A quick diagnostic test is typically a code read using a scanner connected to the OBD2 port in your car. It can pull stored and pending trouble codes from your car, identify which system flagged a fault in your car, and clear codes from your car.
A full diagnostic test is more involved for your car. A shop may use a scan tool or specialized diagnostic equipment to scan multiple modules beyond basic engine codes review, live data streams from multiple sensors in your car, run system tests, component actuations, and check related systems like braking, fuel, exhaust, transmission, and more in your car.
A good car diagnostic test can reveal issues across areas of your car, including:
1. Engine performance issues with your car: A diagnostic test can point to misfires, air-fuel mixture problems, ignition issues, sensor faults, intake leaks, and emissions-related faults in your car.
2. Transmission problems with your car: A diagnostic test can reveal shift solenoid faults, transmission fluid temperature sensor issues, gear ratio errors and communication issues between the transmission and engine control modules in your car.
3. Exhaust and emissions system issues with your car: A diagnostic scan can show problems that cause failed inspections or increased pollution, such as converter efficiency, oxygen sensor performance, evaporative emissions system leaks and EGR system faults in your car.
4. Braking system status with your car: A diagnostic test can reveal wheel speed sensor faults, ABS pump or module issues, brake pressure sensor problems and traction control or stability control faults tied to braking inputs in your car.
5. System and communication issues with your car: Diagnostics can uncover battery voltage irregularities, alternator or charging-related faults, CAN bus communication codes and module faults that may cause issues in your car.
6. HVAC system malfunctions with your car: A diagnostic test may help identify blend door actuator failures, temperature sensor faults, A/C pressure sensor issues and control module errors in climate systems in your car.
7. Steering and suspension issues with your car: Diagnostics can reveal power steering faults, steering angle sensor issues, adaptive suspension faults and stability system inputs that relate to steering behavior in your car.
8. Fuel system faults with your car: A diagnostic test can point to fuel pressure regulation problems, injector circuit faults, fuel trim extremes and EVAP-related fuel vapor problems in your car.
9. Cooling system problems with your car: A diagnostic test can show coolant temperature sensor faults, thermostat performance issues, fan control problems, and overheat events recorded in the module history in your car.
10. Airbag system issues with your car: A diagnostic test can reveal seatbelt pretensioner faults, impact sensor issues, occupancy sensor problems and airbag module communication faults in your car.
A good diagnostic session is not about reading codes and replacing parts in your car. It can also provide context that makes troubleshooting, such as freeze frame data, pending codes, readiness monitors, live data readings and intermittent patterns in your car.
However, a diagnostic test cannot confirm the exact failed part without testing to detect mechanical wear that is not monitored, guaranteeing that the only problem in your car or replacing it through a physical inspection of your car.
You can get a car test at auto repair shops, dealership service departments, or independent shops that specialize in your vehicle make, like your car. The cost of a diagnostic test varies based on whether it’s a scan or a full diagnostic, the complexity of the issue with your car, and your vehicle type.
When choosing a shop, ask if they perform a diagnostic or just a code scan for your car. This will tell you how thorough the process will be for your car. A car diagnostic test is a tool. It is not magic for your car. Think of it as a roadmap that still needs verification before buying parts for your car.
Considering Local Labor Rates
When you take your car to the shop, you should find out if they apply the fee toward the repair of your car.
A quick scan of your car is often cheaper than a full inspection. Doing a diagnostic can save you money in the long run if it prevents you from replacing parts that you do not need for your car.
Knowing how to use the results of a car test and avoid mistakes is important for your car.
Once you have the results, here is how to handle them for your car:
- Ask for the codes, such as P0302 or P0420. Not just something like “misfire code” for your car.
- Ask what tests will confirm the cause, like a smoke test, a fuel pressure test, wiring checks, or a compression test for your car.
- Be careful if someone wants to replace parts without verifying the problem with your car.
- If the code was cleared recently, you may need to drive your car for a while so the monitors can reset and the codes can come back for your car.
- If there are codes, ask which one is the problem and which ones are probably just symptoms for your car.
The bottom line is that a car diagnostic test can tell you where your car is having a problem, which system is affected, and what triggered it in your car.
It can show you if there are issues with your engine or transmission, or if you have emissions or exhaust problems, or if there are faults with your brakes or safety systems, or if you have HVAC problems, or trouble with your fuel or cooling system, and more in your car.
Just remember that the code is the start of figuring out what is wrong with your car, not the end.
The best thing that can happen is when the scan results are used with troubleshooting and a technician who finds the root cause before replacing any parts in your car.
A car diagnostic test is a tool. It is just the beginning of diagnosing car problems like the ones with your car, and you should use the results of the test to help you figure out what is really going on with your car.
Choosing A Professional Auto Repair Shop
Here at Scotty’s Automotive in Sussex County, NJ, we will test your system’s pressure, investigate all potential leaks, assess the performance of clutch and control systems, and any more tests needed before we offer our diagnostics recommendations.
If your car or truck’s performance isn’t keeping up, don’t wait until a small issue turns into a full system repair! Call our pros at (845) 720-3584 and let our team diagnose the problem, give you a clear estimate, and get you back on the road safe and sound.