What you don’t know can hurt you

What’s wrong in this picture?

Have a look at this picture of my DB9 – can you see what’s wrong on my Aston? It’s there, staring right at us. Not recognizing it could hurt your pocket book, your Aston, and potentially even you.  I’ll give you a clue – one tire is down an alarming 10 psi. But can you even tell which one?

Which of the four tires shown here is at the correct pressure of 38 psi?

Which tire is the correct pressure of 38 psi?

If you guessed C you’re right, but it was nothing more than a good guess. They were 48 psi (A), 33 (B), 38 (C) and 28 (D). You had no way of knowing by just looking at it.  The visual difference is so minor you would never spot it walking towards your car distracted by its ravishing good looks.

Aston Martin began fitting Tire Pressure Monitoring Systems (TPMS) to all its Gaydon era cars such as the DB9, Vantage, DBS, Rapide, Virage and Vanquish. The early cars were fitted with a system from SmarTire and the later models used Beru. These were the early days of TPMS systems (circa 2004) as a leading-edge safety feature for high performance sports cars. The keyword there is ‘Safety’.

The TPMS System Warning Light and Message

This leads me onto a pet peeve I have with some owners’ comments I read in the online forums. Inevitably someone will post about the TPMS warning light coming on signaling an issue. They will dutifully check their tire pressures manually, discovering that they are normal, and surmise there is a problem with the sensor or system, asking the group’s advice on how to defeat the warnings to just make them go away. I don’t get this approach! If your airbag warning light comes on, is your first instinct to remove the bulb to make the warning go away, or to diagnose and fix the airbag that may someday save your life?

They might argue that they “can tell” if their tires are at the correct pressure by just looking at them, and the TPMS is unnecessary.  I say BS.  My example above should make it clear that it’s difficult to spot a pressure issue with a low-profile high-performance tire unless the tire is nearly entirely flat and it’s too late.   Aston recognized this issue and went to the trouble to fit a TPMS system to keep you safe.

I have a challenge for you.   Walk out to your Aston after reading this and use your manual tire pressure gauge to check all four tires pressures.  I will bet your car won’t be at exactly the right tire pressures (36psi front, 38 psi rear for my DB9).   Were yours?   Were they off by 2 psi?  5 psi?  More?

Incorrect tire pressures have many negative effects on a car. Low pressures can lead to poor gas mileage, irregular tire wear, and poor handling. Uneven pressures (side to side) causes poor handling. If you’ve been driving with very low pressure you have probably already done significant damage to the tire’s internal structure, making it unsafe even if repaired and re-inflated. A very low pressure tire that overheats and fails at highway speeds destroys the tire, potentially damages the alloy wheel, and could cause an accident. Replacing a damaged tire needs to be done in sets, so you’d be looking at replacing at least two $350 tires (plus towing to a shop, mounting and balancing). If the alloy wheel gets damaged that’s even more expense. And if you were going 100 mph when the tire failed you’ll also need a new set of knickers!

I implore you – when your Aston develops an issue with the TPMS system, put your efforts into repairing it, not defeating it.

The TPMS Sensor is integral with the valve stem

The TPMS system is simple enough. Each wheel has a tire pressure sensor mounted in it as part of the air valve assembly. They continuously monitor the pressure and temperature of each wheel, transmitting the information wirelessly to a central control unit in the car. Each sensor broadcasts a unique ID so the controller knows which wheel is which and can ignore signals from other cars.

The four sensors send their signals to a central TPMS control unit mounted in the car. In turn, it communicates with the rest of the cars electronic systems and can turn on the Check Tires warning light.

SmarTire TPMS Controller

Aston fitted the early model cars with the SmarTire brand of sensors and controller. Today it’s disappointing that it doesn’t actually show the specific tire pressures on the dash display. Our only clue is the “Check Tires” warning message. If that is lit we have to stop and then check the separate control unit display (located in the trunk or under the passenger’s dash) to determine which tire has an issue. A colored LED will tell us if it’s the Red, Green, Blue or Yellow sensor. These correspond with the color bands fitted to the air valves on each wheel.

SmarTire TPMS Battery Soldered to the circuit board

You may have already spotted the Achilles heel in the system – the TPMS sensors in each wheel are battery powered. Like any battery, they won’t last forever. The ones in my 2005 DB9 lasted about 13 years. When the battery finally dies in a sensor it stops transmitting. The TPMS control unit detects that the wheel isn’t sending any information, turns on the Tire System Fault warning message, and flashes the appropriate LEDs so that you know it’s a problem with communication to the sensor, not a problem with the tire pressure. You should manually check the tire pressure to be sure and then move on to fixing the sensor.

Unlike a digital watch, you can’t just replace the battery in a TPMS sensor. You must replace the sensor entirely and then “train” the TPMS controller to talk to the new sensor (since the ID of the sensor has changed), which requires special equipment. Replacing the sensor requires removing the road wheel and dismounting the tire. Aston isn’t helping here either – the cost of the SmarTire replacement sensors is ridiculously high at $380 each from a main dealer! [Or about $265 USD each if you buy them online] And if you have one sensor fail, you can expect the batteries in the other three are also near the end of their lives. I would recommend you replace all four at the same time when you are in the shop. You are probably looking at a ridiculous $2,400 expense to replace all four sensor at a main dealer (ouch!). Undoubtedly this is why some owners try to defeat the system rather than repair it.

You might be thinking that you can save a few dollars by circumventing the Aston dealership by buying the SmarTire sensors somewhere else. Alas, the SmarTire company was bought out by the Bendix company back in 2010 and the only source for the official sensors now is Aston Martin.

Autel MX Sensor

An alternative to replacing with the official SmarTire brand sensors could be a lower cost aftermarket sensor. These generic sensors (like ones from Autel) can “clone” the signal from the original sensor, essentially looking and working exactly like the original sensor, and may not require the TPMS controller to “learn” them. This could potentially be done at an independent specialist or even a well-equipped tire shop. If you did this preventatively (maybe once the car is 10 years old and the original sensors are still working), and combine it when you are getting new tires fitted (so there is no extra charge for the tire dismounting and balancing), the costs could be as little as $130 total. This would be the approach I would take.

Generic Bluetooth TPMS Sensor Valve Caps

If you wanted to entirely abandon the original TPMS system fitted by Aston there are aftermarket systems you can add that link to your smart phone. The simplest of which are just special tire valve caps that transmit via Bluetooth to an app on your phone. The cheapest of these can be found on Amazon for under $50 for a set of 4. I can’t attest to the quality or reliability of these systems [I’d actually recommend the Autel route], but something is better than nothing.

My advice is to regularly check and adjust the tire pressures on your Aston (at least once each season – not just with annual service). And between those manual checks count on your TPMS system to keep you safe.


[Update]  Writing this article for AMQ has inspired me to further pursue how to repair or replace the sensors in detail.  Spoiler alert – I’ve done it and it’s very simple using the Autel sensors.   I’ll be publishing a series of articles and videos all about the process in the weeks ahead.  In the meantime, don’t waste your money buying SmarTire sensors at the dealer (and don’t defeat the system either).


Aston Martin Quarterly Magazine

I originally wrote this article for the Summer 2021 edition of the Aston Martin Quarterly magazine  (you can find the original magazine format of the article here).  I modified the article ever so slightly for this online version since I could link to other websites, etc.

I think all Aston owners should be active members of the Aston Martin Owners Club (AMOC) and with that you’ll receive (amongst other benefits) the quarterly high quality coffee table editions of the AMQ magazine.  If you aren’t yet an AMOC member, please consider signing up here.

6 thoughts on “What you don’t know can hurt you

  1. Neil Dobier

    Awesome. Many thanks for another great article. My car doesn’t have a TPMS system fitted, so the Bluetooth caps sounds like a good idea 😎

    Like

  2. krazylegz

    Great stuff as usual Steve. Is it possible to program the Autel sensors before installing them? Maybe I want to buy them now, program them, but not replace my tires for another year. Thanks for all the hard work!

    Like

  3. tonymillman

    Thanks Steve good write up and good to know Autel is an alternative. regards Tony ps it is also interesting that some tire shops when repairing a tire have no idea. I had a tire repaired on my maserati hit some standing water at reasonably what I thought sensible speed and almost lost control. I could not understand why as it had never happened before and the next day I checked my tire pressures and the one they repaired was 47psi the others were all as advised by the manufacturer. At another time I found 2 loose wheel nuts. I am very cautious now who touches my car, always run a tire wrench over the wheels after a service and always check pressures.

    regards Tony.

    Like

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