Is this one of the early third generation cars? Most of them had their engines rebuild. They can check with the VIN.
Service history does not mean a lot. Yes they change the oil and if they remember the filter, but as the engines are not designed properly, they require extra maintainance which is not in the booklet, e.g. injector seals, oil pick up, cleaning EGR, manifold, turbo, etc.
If on the other hand, this is an approved used car, you use the 12 months warranty to rebuild the engine.
I am not sure about the compression threshold but the third generation engines are low compression. So that could mean that they have very little tolerance on how much they can lose out.
If you have still have any warranty, ask them to clean the EGR, and find out whether the warning light will go off. If nothing happens, it could be for an engine rebuild as they guess.