When I start my DB9 on the first cold day every fall it greets me with a scary “Check Tires” tire warning alert on the instrument cluster. In frustration and alarm about all I can think is “Now what!”. As it turns out this hasn’t been a big deal.
When the ambient air temperature falls, air gets denser. Consequently, this causes the air pressure in a cold tire to drop slightly. In our DB9’s, if the pressure drops below 30 psi the alert will trip the Tire Pressure Monitoring System (TMPS) to warn you of a potential issue. A small pressure change isn’t the end of the world, but we need to follow up. You can learn more about the TPMS system and what will cause an alarm in my more detailed article here.
I check the pressure in my DB9’s tires a few times each year, and when I set them in the summer the ambient air temp is usually 85+ degrees. In the fall where I live (Northern California) the ambient temperature can drop to below 40 degrees, a 45+ degree change. This appears to be enough of a change to trip the alert each fall.
The next logical step is to get out of the car, open the trunk and look at the brains of Tire Pressure Warning system mounted along the top. There are five (5) colored LEDs on the device, and you should discover at least one lit up solid and the rest blinking. The one that is on solid is the one with a pressure problem. In this occurrence on my car it was the Red LED that was solid (meaning the left front tire had an issue). Each color corresponds to a specific wheel (that’s that those little colored bands are around the tire valve stem). 
They are:
- Yellow – Left Rear
- Red – Left Front
- Green – Right Front
- Blue – Right Rear
[Note: My car is a 2005, and later model cars may have a more integrated TPMS system, or even just tell you which tire is low and its pressure. Early model owners need to follow this more manual approach].
Once you know which tire is alerting, grab your tire pressure gauge and check the pressure of that wheel (you can check out my other article on how to do this). If its below 30 psi, you can confirm this is the problem tire. Personally, I would recommend you check all four tires while you are at it since the others will likely be close to the same issue.
The solution now is to top up your tire pressures. If you have your own compressor just add air to reach the ideal pressure of 36 psi in the fronts and 38 psi in the rears. If you don’t have a compressor, and the tire is just down a couple of PSI, you can still drive safely to the nearest gas station and top of your pressure there.
Once you’ve topped up the pressure back to normal, the alert should clear. You may need to turn off the car completely and start up again for the TPMS to recognize the issue is resolved and clear the alert on the instrument cluster.
Warning: If you top up the air and the problem returns quickly on the same wheel, this is likely not because the outside air temp has dropped and you may have a puncture in the tire. Time to take the car to a tire repair specialist immediately. Don’t drive on a tire if the pressure is below 20 psi. Don’t drive very fast or very far either or you risk damaging the core of the tire and it will need replaced (at significant expense since they have to be done in pairs). And I wouldn’t use the can of tire repair ‘Goo’ in the toolkit of the Aston unless I was desperately stranded roadside. That Goo may solve the problem temporarily, but you’ll be messing up the inside of the tire, the TPMS and the wheel rim. My tires have been ‘Screwed’ a few times, check out this article.
Video
Here is a quick video of the experience I recorded on one of those days….
There are lots of reasons you might Torque the Wheel Nuts on your DB9, but its anytime you’ve had a wheel removed or perhaps you are getting ready for a track day and should double check they are properly torqued. I can tell you there is absolutely a wrong way to do it – just using an impact wrench and hammering them on until the gun stops turning. Read on to learn the right way. 
Aston 1936 