Once upon a time, if you wanted to make sure that your car’s tires weren’t underinflated, you used a pressure gauge and checked each one manually. You might still do that, but you’re a mechanic and prefer to do things yourself. Consumers are much more likely to do nothing – their TPMS light will tell them if there’s something wrong with a tire, and they can go from there.
Of course, all mechanics who’ve been around the block a time or two realize that TPMS technology isn’t everything it’s cracked up to be. In fact, when your customer cannot get that little amber warning light on their dash to go off, they’ll be bringing the vehicle to you. They might even do that in the first place, without checking to see if a tire is even low. This leaves you dealing with a range of potential TPMS issues. What should you do?
The Obvious – Check Tire Pressure
On the off chance that your customer simply did not check their own tire pressure, but brought their car to you straightaway, or their gauge was inaccurate, start with the most obvious thing. Check the pressure in each tire. First, check the driver-side door placard to verify the OEM-stated pressure in the front and rear tires, and then use an accurate (yes, accurate, and that usually means digital) tire pressure gauge. If you find that one or more tires is underinflated, add air and drive the car for a bit. If the TPMS light goes out, that’s all the issue was. Note that it’s probably a good idea to give any tire low on air a once over to check for punctures before sending your customer on their way.
It’s a Spare
Your customer was minding their business, driving down the road, when a tire blew. They knew enough to pull off on the side of the road, jack up the car and put the spare on, but now the TPMS warning light is on. What gives? Actually, chances are good that the issue is the spare. While some OEMs do put TPMS sensors in the spare, most don’t. As long as the TPMS unit is not receiving signal from one wheel (the missing sensor), the warning light will stay on. Repair the flat, air it up to spec, put it back on and drive it. The light should go out.
More Complicated TPMS Issues
The two examples above are very common, but they’re also the simplest TPMS issues to fix. You could encounter a number of others that will require you to dig more deeply into the situation.
Damage to the TPMS Sensor: This is perhaps the single most common cause of TPMS issues other than vehicle owners simply not understanding how the system works. It’s usually found after the customer has a new set of tires installed – when removing the old tire, the installer’s tire machine blade hits the sensor, cracking the housing or otherwise damaging it. This renders the sensor inoperable, and it will need to be replaced and the relearn procedure performed to make the warning light go out.
Bad or Failing Sensor Battery: One common cause of TPMS issues is a bad or failing battery in one or more TPMS sensors. Each sensor has its own battery, which allows the sensor to monitor pressure and send signal to the TPMS unit. Generally, sensor batteries are good for between seven and 10 years. However, frequent driving and long-distance driving can greatly reduce this lifespan (the more frequently a car is driven, the more use a battery sees and the faster it will die). Replacing the battery and performing the relearn procedure should turn the light off.
TPMS Sensor Wiring or Antenna Fault: While the battery provides the power needed for a TPMS sensor to operate, it must communicate with the TPMS unit via its internal wiring and antenna. If there is a fault in either, or there is damage to either, such as corrosion from moisture or age-related deterioration, it can cause issues with the system. Replacing the sensor and performing the relearn procedure is the only way around this particular issue.
Bad or Failing TPMS Unit: In some instances, the problem with the TPMS is not with any of the wheel sensors. Rather, it’s due to a problem with the TPMS unit, such as a short or overvoltage situation. To verify if this is the case, you’ll need a TPMS monitoring tool. Connect it to each of the tire pressure sensors and make sure that they are sending and receiving signal without an issue. If they are all in working condition, the problem is going to be with the TPMS unit itself.
Relearn Procedure Was Not Followed After Tire Replacement: Tire replacement without having a relearn pattern will make the warning light stay on in the dash. If your customer has had tire replacement recently and the sensors are testing fine, then it could be something as simple as needing to do a relearn. However, many modern vehicles have an auto-relearn process that does not require you to attach an OBD II reader. If the make/model has an auto relearn process, this is most likely not the problem.
The single most important thing to do is to purchase an accurate TPMS tool, and to ensure that you are using an accurate digital pressure gauge (not the cheap, spring-loaded analog type). Test each of the four wheel pressure sensors, and then move on from there. In almost all instances, the problem will be an issue with a particular TPMS sensor, but you cannot simply replace them all and call the job done.
Eliminate the most common issues we mentioned above, and then make sure that the issue is not with the TPMS unit itself. Your customers will be happier with your accuracy (and the lower cost as opposed to replacing multiple tire pressure sensors), and you’ll find that dealing with TPMS issues is not nearly as frustrating.