The oil pressure light came on for a moment and then went out. Can I keep driving it?
On the Ingenium diesel we would rather you did not, and that is not a sales line. The oil pump on that engine is driven by a belt that runs inside the engine in the oil, and as it ages it sheds material that collects on the oil pick-up. The first sign of that is exactly what you describe: pressure that drops at idle and recovers with revs. It is cheap to check pressure directly against what the sensor is reporting and to look at the oil for debris, and it is very expensive to find out by carrying on. If your car is the petrol version the same warning still gets checked properly rather than treated as a faulty sensor.
My XJ sits low on one side in the morning and comes up when I start it. Does it need new struts?
Maybe, and maybe it needs a fitting and a length of pipe. A car that sinks overnight and levels itself when started is leaking air slowly, and on these saloons the leak is often at a push-fit connector, along a nylon line, or at the top of the strut rather than in the strut body itself. We read what the suspension module recorded for each corner, leave the car standing and read it again, then pressurise the system and find the leak physically. The reason for doing it in that order is that the compressor is the part that eventually dies of a leak nobody found, so replacing a corner without testing the pipework can leave you with a new part and the same car, and a burnt compressor later.
The screen keeps rebooting. Is the infotainment unit finished?
Not necessarily, and it is the assumption that costs the most on this make. The screen is one module on a network, and it behaves like this when the supply sags, when an earth is poor, or when another module on the same bus stops answering and drags the conversation down with it. So we scan every module, read the communication entries and look at whether the faults all carry the same timestamp, then check voltage at the unit and the state of the battery and charging system. If it does turn out to be the unit, we will also tell you honestly whether a replacement can be programmed outside the franchise, because on some of these it cannot.
The battery keeps going flat when the car stands for a couple of days. What do you actually do about that?
We lock the car and leave it until the network has genuinely gone to sleep, then measure what the car is still drawing and compare that with what it should settle to. If it is high, fuses come out in order and the figure is watched until the circuit and then the module responsible is named — very often something in the keyless entry or body side keeping itself awake. It is a slow job by nature, and that is the honest version of it: the fast version is selling you a battery, which works until the following weekend.
Do you work on Jaguars the same way you work on Land Rovers, since they share engines?
Some engines are shared and some faults genuinely are the same job. But the cars are not interchangeable and we do not treat them as though they were. A Jaguar saloon and a large four-wheel drive put entirely different loads through their suspension, carry different body electronics, and arrive with different complaints. The useful answer for you is not which badge is on it, but which engine and which platform your car has — that is the first thing we establish, and it decides what gets tested first. We will tell you when your car shares a known fault with another model, and we will tell you when it does not, rather than applying a story that belongs to a different vehicle.
