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Haynes’ World: up close and personal with TPMS

TPMS reset

Haynes' World is a regular feature that looks at what the staff at Haynes are doing with their cars, bikes and other vehicles. This time, Rob gets out his tyre gauge and checks for a puncture.

Car: BMW 2 Series

Owner: Rob Keenan

Does the merest mention of a tyre pressure monitoring system (TPMS) give you heart palpitations? All new cars are sold with them; you may have had a warning message ping up on the dashboard at some point.

I’ve owned two cars that had them, both BMWs. The first, an E92 3-Series, was fitted with run-flat tyres so didn’t have a spare wheel. But there was at least some guarantee that if the dreaded bongs sounded, I’d be able to continue my journey – albeit at a reduced rate of knots. And indeed, I did suffer a puncture and was very grateful for TPMS.

My current car doesn’t have run-flat tyres or a spare wheel (the latter is pretty rare as a standard-fit thing these days). Instead there’s a bottle of sealant (or gunk) and a compressor (shown below) – and having heard stories from friends over the years, I have very little faith they’ll work as intended.

Tyre gunk and pump

How does a puncture repair kit work?

Mine is an OEM kit; the compressor connects to the bottle which is then screwed to the tyre valve, so the tyre is inflated while the sealant is pumped in. Once the tyre pressure is up to 2.5 bar (36psi), you then need to drive at 15-35mph for between two and six miles, which isn’t ideal on any road let alone a motorway. And once the sealant has been pumped in, it’s game over for the tyre – you’ll need to buy a new one.

You’ve probably seen the aftermarket cans of gunk for sale – I have even less faith in them. I nearly got the chance to find out on holiday last year, when the hire car picked up a nail (again, I was alerted by the TPMS), but when I lifted the boot floor there was an empty can of sealant staring back at me (shown below). Which made me wonder if the car was still running on a tyre full of gunk.

Moral of that story: always check that your hire car has some form of tyre repair/wheel replacement on board before you drive off. 

Can of tyre sealant

So TPMS is a useful thing to have, but it has an annoying habit of pinging off warnings under certain conditions: during cold weather and often when hot, dry tyres cool quickly when they encounter a wet road. In both situations the tyre pressure drops slightly, but it’s enough to trigger the sensors.

How to reset TPMS?

I had two TPMS warnings last winter, and once I’d checked the pressures myself, with a digital tyre gauge I keep in the boot, the system is easy to reset via the car’s iDrive (shown below).

My parents have a Mk3 Honda CR-V without an infotainment screen, and the TPMS is a nightmare to reset. I’m pretty tech-savvy but I have to reach for the car’s manual each time to be shown which steering wheel buttons to press to work my way through menus on a small screen between the driver’s analogue instruments. Horrible.
 

Reset TPMS BMW

On balance, I’d rather have a car with TPMS than not, but I find myself spending an inordinate amount of time thinking about the amount of technology in new cars, and the likelihood of financial ruin should it fail. I was extremely lucky to avoid a £2000+ bill when my iDrive control unit failed when the car was still (just) inside the warranty period.

Maybe my learned colleague Euan has the right idea? He runs a base-spec Skoda Yeti that has all of the essentials (electric mirrors and windows) you can fix yourself but none of the luxuries (touchscreen, reversing camera etc) you’d probably have to get a garage to look at.