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“Without the car diagnostic scan, it’s crystal ball time”
“The days of setting points and tuning carburettors are long gone”
“What are you paying for when your mechanic (now technician) plugs in his seemingly magical computer?”
“A car diagnostic scan alone will not fix your car”
Car Diagnostic Scan – What are you paying for?
Yes, it’s happened, cars have evolved. The modern car is now a rolling network of computers with dozens of connected sensors and actuators. The days of setting points and tuning carburettors are long gone. The DIY mechanic is dead (for the most part). It’s all about the car diagnostic scan these days, but what are you paying for when your mechanic (now technician) plugs in his seemingly magical computer?
When you car logs a fault code, one or more of your car’s sensors has signalled a value that is out with its pre-programmed range of “plausibility”. The connected electronic control unit (ECU) then checks to see if the fault code satisfies a number of preset conditions (fault frequency & priority) and decides whether or not a permenant fault code should be logged and if the driver should be informed. Perhaps you’re familiar with this next bit… The driver will then be made aware of the fault via a warning light on the car’s instrument display.
So, you’ve done the right thing. You’ve taken your car to the garage and have crossed you fingers, hoping that it won’t cost £££s to get that warning light off your dash. At this point it is important that the garage you have trusted with your car has a competent diagnostic technician on the payroll. Here’s where the car diagnostic scan comes in, and the technician needs to be on point when it comes to getting around the car diagnostic equipment at his/her disposal. Without the car diagnostic scan, it’s crystal ball time.
The point I made earlier about crossing your fingers…I was only half joking. There are literally hundreds of potential causes (some wildly more expensive than others) for a fault being logged and a warning light becoming active on your car’s dashboard. So please don’t think less of your mechanic (technician) when he/she can’t diagnose the fault or provide a quote over the phone.
The car diagnostic scan is the essential first step in the diagnostic process. Without the car diagnostic scan, fast and efficient diagnosis of your car’s fault is simply not possible. To begin the car diagnostic scan your technician will select the ECU reporting a fault(s) and interrogate it with a diagnostic interface. Car diagnostic interfaces and software don’t come cheap and the likelihood is your local garage paid thousands of pounds for their kit, so please be understanding when there is a fee for the use of the equipment (this is normal practice in a modern garage). A communication link is made between the car diagnostic software and your car’s ECU via a car diagnostic interface. This allows the technician to view the logged fault(s) and observe car diagnostic data in real time as it is signalled to your car’s ECU.
You diagnostic technician is now armed with critical information related to your car’s fault, and should have a trajectory for continuing the fault finding process. Unfortunately, the information gatherer by the technician via the car diagnostic equipment does not magically fix the fault, nor does it tell the technician what part to replace. There are hundreds of fault combinations on modern vehicles.
As smart as you think your fancy modern car is, it’s essentially pretty dumb. For example, it may report a fault like “fuel pressure sensor – signal too high”. This doesn’t mean the technician gets on the phone to the parts supplier and orders a new fuel pressure sensor (or at least, I hope it doesn’t). The ECU has no idea why this fault code exists, and believe me, there are plenty of faults that can cause this type of fault code to be logged. For talking sake, let’s assume this circuit integrity to be good and that the fuel pressure is indeed signalling above the specified upper limit, and it wasn’t caused by say, and electrical short to positive on the signal wire. The technician must investigate why this has happened…is the high pressure regulator working correctly, are the injectors leaking back the correct quantity, is the high pressure pump integrity okay, etc, etc. You can see where I’m going with this. The car diagnostic scan is just the beginning of the fault finding process and, although essential, doesn’t come close to rectifying the fault(s) or doing the technicians job for him.
You’re now aware of the importance of the car diagnostic scan, and how it fits in as an essential, integral part of the complete diagnosis of modern vehicle faults. Most car repair garages have some sort of car diagnostic equipment these days, but a car diagnostic scan alone will not fix your car. It is therefore essential that your chosen garage has a capable and qualified car diagnostic technician. Save money and ensure you get this! If you’re Glasgow-based, our IMI-recognised Advanced Automotive Engineer will be happy to help. So drop us a line 😀
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