The DB9 is equipped with a Tire Pressure Monitoring System (TPMS) that includes Tire Pressure Sensors (TPS) mounted to each wheel. They are an integral part of the air valve. You’ll notice that each of your air valves has a colored ring around it, either Red, Green, Blue or Yellow. In your trunk / boot is a mysterious little box with LEDs. This is the TPMS indicator panel, and if you ever get a warning indication on the dash, you’ll need to check the LED’s and see which color is lit, and that’s the tire with the issue.
During service the main thing we can do is make sure the correct sensor is on the correct wheel. The documentation says the TPMS is expecting them in these positions:
- Yellow – Left Rear
- Red – Left Front
- Green – Right Front
- Blue – Right Rear
It is possible that during a set of new tire installations or service a tire technician could have missed this detail, and installed them on the opposite sides. It’s easy to check, so have a look.
If you find them out of place, be careful to avoid just swapping the rim and tire to the other side. Remember these tires are unidirectional, and if you move the right front to the left front, the tire will now be spinning in the opposite direction than it was, and this is not good. You actually need to have the tires dismounted and remounted (and rebalanced) as you swap rims (the right front tire needs to always be on the right front after you’ve driven on it a few miles).
The TPMS does more than just report the current tire pressure, it actually alerts us to three conditions:
Low Tire Pressure
If the tire pressure is below 30 psi it will alert us.
I get this alert occasionally as the seasons change from Summer (where I live it gets to 100°F) to Winter (as cool as 32°F). This ambient temperature change is enough to drop the cold resting temperature of the tire a few psi, so it sets off the alert and I get off my ass and set my tire pressures for the season. Remember to reset the tire pressures at least once per season.
High Tire Temperature
If a tire is above 170°F it will alert us. This could happen if you are pushing your tires very hard (on a track) and they are overheating, or if they are dangerously low and they are overheating due to sidewall flex. Either condition is dangerous and you should stop and deal with it appropriately.
If a tire goes through a 5 psi pressure change during a driving session it will alert us. This is to catch a leak that’s just started before we get into trouble. For example, if your tire was 38 psi when you started a trip and you picked up a nail and a leak, it will go into alarm at 33 psi during the same trip.
Here is a quick video about this.
You might want to check out these other posts relating to your tires: