"They plugged in the diagnostic tool, found no fault codes and said everything was fine." I hear this all the time. But listen, my friend, just because your car hasn't logged any faults doesn't mean it's healthy. Diagnostics isn't just about plugging in a scanner and reading fault codes. You need to look at the live data too, what we call measuring blocks. That's often where the real problem shows itself.
What do measuring blocks actually tell us?
They're the readings your car is reporting right now — engine speed, temperatures, pressures, corrections and component positions. They show us how each system is actually behaving, not just whether it's logged a fault. And do you know what's interesting? Some problems show up in these readings long before the engine management light comes on.
What do we check in VAG live data diagnostics?
- Fuel trim corrections — whether the engine is trying to compensate for an air leak or a fuel supply problem.
- Misfire counters for each cylinder — whether any of the cylinders are misfiring.
- Fuel pressure.
- Camshaft timing deviation — this can help us spot a stretched timing chain.
- How much soot is in the DPF and when it last carried out a regeneration.
And what do we check in the DSG's live data?
- Clutch readings — these help us work out how worn the clutches are.
- Hydraulic pressure.
- Gearbox oil temperature.
- How many times the gearbox has changed gear and what its adaptation values look like.
Why is this so important when you're buying a car?
Because someone could clear the fault codes just before you turn up to view the car. You plug in the scanner, nothing comes up, and you think everything's fine. But here's the catch! Live data isn't nearly as easy to hide. A stretched timing chain, worn clutch or blocked DPF can all leave clues in the readings. And those are exactly the things you want to know about before you hand over your money for the car. Not afterwards.
Don't assume everything's fine just because "the scanner shows no faults". If nobody has checked the live data, they could miss a serious problem. And if you buy the car like that, you'll be the one paying for the expensive repair out of your own pocket.
How do we carry out diagnostics at Das Auto Service?
- First, we read the fault codes from every control module in the car.
- Then we check the live data, both with the car stationary and while driving it.
- We compare the car's actual readings against the values specified by the manufacturer.
- Finally, we explain what we've found and what needs to be done.
Advice from Kris Mladenov: If your car only plays up occasionally, tell us exactly when it happens. Is it when the engine's cold, once it's warmed up, under acceleration or in some other conditions? That really helps us record the live data at the exact moment the problem appears.
If you want to know what's really going on with your car, rather than simply whether it has any stored fault codes, come and see us at Das Auto Service. We'll check the live data and explain what the readings are telling us. Because plugging in the diagnostic tool is only the first step. The real diagnostics start after that.
Read more
- Vehicle Diagnostics at Das Auto Service
- Pre-Purchase Vehicle Inspection
- Lambda Sensor and Catalytic Converter: When Are They Really to Blame?
- Buying a Car with DSG: How Do You Check the Gearbox Before Buying?
- Compression, Leak Tests and Borescope Inspection: How We Check Engine Health
- How Can I Check a VAG Car's Genuine Service History?
- VAG Coding: What Can You Enable and What Can't You?
Frequently Asked Questions
What are measuring blocks?
They're live readings that your car's control modules report in real time. They help us see how the different systems are actually working.
If there are no fault codes, does that mean the car is healthy?
No. Plenty of problems show up in the live data long before the car logs a fault code.
Can diagnostics tell if the timing chain has stretched?
Yes. We check the camshaft timing deviation, which can reveal signs of a stretched timing chain.