When I purchased my DB9 used and was doing the initial walkaround, I opened the trunk and asked the sales rep “What’s this thing with all the LEDs?”. It wasn’t a main dealer, and the rep didn’t know. I figure there might be other owners out there that don’t know what it is, or what all the LEDs mean. Let me explain….
Gaydon Era Aston Martins (DB9, Vantage, DBS) used a Tire Pressure Monitoring System (TPMS) made by SmarTire. Back in 2005 having a TPMS was exotic. Fast forward 15 years and every car sold has some form of TPMS. In around 2010 SmarTire was purchased by a larger company Bendix, and ceased making passenger car systems (Bendix is largely used in commercial trucking). Aston Martin then switched to a company called Beru.
Aston Martin must have had an iron clad contract for spare parts and you can still purchase a replacement wheel sensor from them (for a dear price). You cannot buy an actual SmarTire sensor from Bendix. As many cars are now 10+ years old, many of the sensors are now failing and owners are looking for options.
The SmarTire system is comprised of a Control Unit and four Tire Pressure Sensors. Each sensor is actually mounted in the wheel and is the air stem. You may have noticed that each tires air filler stem has a colored plastic ring (or should unless its been lost). The colors correlate to the specific wheel positions and should be:
- Yellow – Left Rear Tire
- Blue – Right Rear Tire
- Red – Left Front Tire
- Green – Right Front Tire
In the very early DB9’s (2004 to 2006?) the SmarTire control unit is mounted in the Trunk (Boot) along the top center edge (as with my car in my photos above). It seems somewhere around the introduction of the Volante and Vantage (MY 2006/2007?) they relocated it in the cabin under the Glove Box area out of sight for all models as seen here.
How it works
Each wheel sensor is BATTERY powered. Yikes! That means they were NEVER going to last forever. Mine gave up a few years ago and I opted to replace them (they lasted 13 years). Since they are battery powered they do have some smarts in them. They turn off when the car is not in motion for an extended period of time. Essentially when parked, they aren’t transmitting.
After they sense wheel rotation, they power up and begin transmitting at 433.92 Mhz. They are sending out more information that just the tire pressure, they also transmit the temperature of the tire. This is important as well if the tire is overheating due to overload or low pressure. Both are dangerous conditions you want to be alerted to.
All four sensors are transmitting, and listening is the control unit. The control unit is programmed by Aston to know that the target tire pressures are (36 psi up front, and 38 psi rear). Check out my article on properly setting the tire pressures. It keeps track of the sensors data and will alert you to many conditions:
- Tire pressure low
- Tire pressure VERY low
- Tire over temperature
- Tire pressure ‘changing’ at a pace faster than it should
- Sensor Failure
- Control Unit failure.
Where the system shows its age is that we don’t get a nice dashboard display showing individual tire pressures (like in many modern cars today). You simply get a warning light and one of two text displays “Check Tires” or “Tire System Fault”. Then, you have to stop, get out, and look at the Control Unit LEDs to work out what else is happening. That’s why I am writing this article, so you can understand the LEDs.
Ever start you Aston and leave it idling for a long period of time without driving off? You’ll most certainly get the “Check Tires” warning on the dash. This is because the Control Unit is all started up, but none of the Tire Pressure Sensors have turned on and started transmitting yet, so it thinks all four of them have failed. Not to worry, just eventually start to drive somewhere, the sensors will turn on and start to transmit, and the error will automatically clear. Usually within a block or so.
Not really a quirk, but you will likely get low pressure warnings in the Fall as temperatures start to dip. Tire pressure is temperature dependent, and if you last adjusted your tire pressures on a hot summer day, its likely they will be at least 4 psi lower on a cold fall morning. Just heed the warning and top up the air in your tires. Check out my article on Seasonal Tire Pressure Warnings here.
Understanding the System
The SmarTire Control unit has 5 LEDs.
- Control Unit System Status
- Yellow Sensor – Left Rear Tire
- Blue Sensor – Right Rear Tire
- Red Sensor – Left Front Tire
- Green Sensor – Right Front Tire
When you first turn on the Ignition Key, the system will begin to power up. If you look at it during this time it’s lit up like a Christmas Tree. All the LEDs will cycle through all the colors so you could diagnose if an LED had died. This only take a few seconds.
After it’s powered up, it automatically begins to listen for the four tire pressure sensors. While it’s waiting for them to check in, you’ll see the System Status LED blinking amber, plus each wheel sensor that has not yet checked in will be blinking amber. If you’ve started the car, and it’s still sitting parked in the garage, this is the way it will stay until you start to drive off. Remember, the sensors don’t turn on and start transmitting until the vehicle is in motion for a bit.
Once the first sensor checks in the LED for that sensor will turn off. The System Status continues to flash amber since other sensors have not checked in. In this example, the Yellow sensor is communicating properly.
As you drive a little further the rest of the sensors will check in, and in this example all but the Blue sensor have checked in.
Keep in mind that when a sensor does ultimately fail (battery deleted after a decade or more) they typically all don’t fail at once. Your first sign of this will be a single sensor that fails to communicate even after driving around. See the signs of that below.
Once you have driven far enough to wake up the four sensors and they’ve checked in with the Control Unit and all the pressures are fine, you’ll see the System Status LED turn to Solid Green and all the sensor LEDs will be off. This is what you hope for all the time. Green is good.
When Problems Occur
Your first sign of a problem will be a warning message on the Drivers Information Module (DIM) and a TPMS idiot light. This is your call to action.
Stop the car and go examine the LEDs. It should point you at a problem with a single tire. Respond accordingly checking the tires pressure, looking for a puncture, etc. DON’T just keep driving assuming its some minor electronics quirk!
This is telling you that you have a problem with one or more tires pressure.
If the LED for a specific tire is SOLID Red, this means the pressure is at least 25% low. Since normal tire pressure is 36 PSI, getting this warning means you are already at least 9 PSI low on pressure. Something is wrong. It could be even lower, this really means 25-49% low. In this example, its telling you the Blue Sensor (Right Rear Tire) is Low.
If the LED for a specific tire is FLASHING Red, this means the pressure is at least 50% low. This is very dangerous to continue driving on. Since normal tire pressure is 36 PSI, getting this warning means you are already at least 18 PSI low on pressure. Something is wrong. It could be even lower, this really means 50-100% low. In this example, its telling you the Blue Sensor (Right Rear Tire) is Very Low.
When the DIM shows “Tire System Fault”
This is telling you there is a problem with communication, either with the Control Unit itself, or one of the tire pressure sensors. If this alert comes up, I’d recommend pulling over to inspect the LED status and follow-up accordingly. Essentially you will be flying blind on either the whole system or at least one tire.
If the System Status light is FLASHING Amber and one of the Sensor LEDs is SOLID Amber, this means that there is a transmitter Sensor Fault. As I noted near the top of this article, the sensors are battery powered, and this may be your first sign that they have packed it in. The fix will be replacing the sensor at a dealer (ugh). In this example, the Blue Sensor (Right Rear Tire) has failed. If you continue driving, just remember you will have no warning of a pressure problem with that tire. Be careful, check it manually, etc.
If the System Status light is SOLID Red, this means the Control Unit itself has the Failure. While this seems catastrophic, this is actually the easier issue to fix. You can buy a refurbished identical control unit on eBay for about $20 USD. It still requires a dealer visit to ‘program it’ to learn each wheel sensor. Here is an example of that a TPMS failure will look like.
Where I gathered my Background
I’ve been learning more about the TPMS system as time goes on. I wrote an earlier article about them years ago when I first got my car (check it out here).
I felt motivated to write this article based on what I learned recently reading through Aston Martin’s Field Service Bulletin (FSB 0297) that was published in July 2009 and sent to its Dealers to help educate the service team. I found this very informative, and used it as the basis for this article and supplemented it with my own additions. You can download all the FSB’s and other interesting stuff if you sign up for an Aston Martin Tech Info Subscription (check out how by clicking here). Here is a link to the entire original article if you’d like to see it.
For those of you that might like to see it in action, here is a short walk around video of the SmarTire TPMS system on my DB9. If someone would be kind enough to shoot a supplement for a Vantage, I’d be happy to include it here. Please contact me on the Contact Page.