Q Every year around the beginning of winter, the Low Tyre light shows up on my Toyota’s dash. I add air and bring the tyres up to the recommended pressure, but the light remains on. Oddly, it shuts off in warmer weather. Can you tell me how to reset it?
A With all tyre-pressure monitoring systems, if your tyres are correctly inflated the warning light should turn off on its own once the pressures are within spec. Before we go down the diagnostics road, we should probably eliminate the pressure gauge as the source of the problem. When temperatures turn colder, the volume of the air in the tyres shrinks. It’s fairly normal to have to fill your tyres with additional air in the autumn or the winter. The thing is, if the pressure gauge is reading wrong it could be telling you the tyre is full when it isn’t. It’s probably worth a few bucks to get a new, high-quality, handheld gauge to make sure you really are filling the tyres to the recommended pressure before you start blaming the car.
Now that you know your tyres are correctly inflated, let’s consider the other options. I’ve seen diagnostic systems stubbornly hold on to warning signals for no apparent reason. If you’re lucky enough to have access to an OBD-II scanner, plug it into your OBD-II port in the driver-side footwell, then turn the key to the “on” position without starting the car. The machine will scan the car’s codes; you should get one in the format of C07XX, which is related to a tyre-pressure-sensor fault. The scanner will give you the option to clear that code, which you should do. Then unplug the scanner, start the car and see if the light stays out. If it doesn’t, one of the in-wheel sensors may be malfunctioning. In this case, Toyota technicians will have to run a system diagnostic.