For a start, don’t drive the vehicle any farther or even start the engine. The car is trying to tell you that it has insufficient oil pressure to properly protect the engine, and continuing to run it will quickly destroy it (if it hasn’t already).

There are many reasons for a car to suffer from low oil pressure, including a too-low oil level, the wrong grade or type of oil, a failed oil pump or a blocked oil filter. Even an overheated engine can cause the oil to become too thin for the oil pump to be able to supply the required oil pressure.

It’s also important not to confuse oil pressure with oil level. The amount of oil in the sump can be perfectly correct, but the engine may still lack oil pressure. Have the car towed to a workshop and have the problem properly diagnosed.

To stay within your budget, any A4 wagon you’re likely to find will be getting on for around 15 years old. A4s from this era weren’t bad cars (they were actually great to drive) but the old expression that there’s no such thing as a cheap, second-hand European car has its roots in the truth.

The fact is, an A4 of any sort will be more expensive to repair and maintain than many, say, Japanese or South Korean cars of a similar size. This isn’t Audi-bashing, it’s just a fact; the Audi is a more complex design and European car parts are just generally more expensive to buy (blame exchange rates).

None of this is to suggest that an A4 can’t be bought and run on a budget, but only to a certain extent. At which point, skipping vital maintenance might seem like a good financial decision but is most certainly not. A complex machine like the Audi is also probably not the best car on which to begin learning about maintenance, if that’s on your son’s agenda.

Audi A4 engine oil changes are a critical part of life for this car, as its high-tech engine is complex and precise and will not tolerate dirty or old oil. But even though the engine is sophisticated, as long as you know how to change the oil correctly, it’s a great DIY way to save money for the home mechanic (oil changes are a major income source for the average service centre) and will empower you to tackle more maintenance jobs including, perhaps, a full service. The best advice is to buy a workshop manual and follow exactly the steps as laid out, but essentially, you’ll need to drain the old oil, replace the oil filter, renew the oil and dispose of the old oil in an environmentally acceptable way (many councils operate oil recycling stations). While not a challenging job for a mechanic, the Audi is a complicated machine with lots of components competing for space, so it’s possibly not a job for the completely uninitiated.

There are several things you need to know before even reaching for a spanner. Those include the type of Audi A4 oil you need, the specifications of the Audi A4 oil filter that will be changed as part of the process, and how often to change oil (often referred to as the oil-change interval). You also need to know precisely what year your car is as Audi varied specifications as the years rolled by. A 2007 A4, for instance, may have different specifications compared with one from 2010, or 2013. Even a 2011 and a 2012 Audi A4 had differences under the bonnet, so be very specific when it comes time to buying the oil and replacement filter. Don’t forget, too, that the A4 has used extensively both 1.8 and 2.0 size engines and, of course, a diesel option which has its own set of specific requirements when it comes to servicing. Again, the workshop manual and the parts interpreter where you buy your oil and filter are your friends. Knowing your car’s VIN can also be a big help in identifying what specific parts you need.

The correct Audi A4 oil type is (for petrol and diesel engines) a fully synthetic 5W30. You’ll need five litres for a diesel oil change and 5.2 litres for the petrol engine-A4. The correct replacement oil filter is a Ryco (or equivalent) R2748K for the petrol engine and an R2740P for the turbo-diesel.