Nowadays, tire pressure monitoring systems are part of most vehicles’ fuel-efficiency system. And whether you like it or not, they are apparently here to stay. But just as any other electronic component, it can fail at some point in your car’s life and you’ll need to spend money to get it fixed. Or you can investigate the problem and locate the faulty part yourself, thus saving time and money by keeping your car away from the repair shop. So what are you supposed to do when one of your sensors go bad and you are facing a tire pressure sensor fault situation?
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What are tire pressure sensors and what are they used for?
Tire pressure sensors are small electronic devices installed inside your tires used to wirelessly monitor the air pressure in real-time while you are driving. Having your tires inflated to the wrong pressure can greatly reduce your vehicle’s fuel efficiency. Over and under-inflated tires can also increase the braking distance required to bring your car to a stop and leads to uneven tire wear and unnecessary early tire replacement costs.
TPMS systems were created to warn you when you are driving with low-pressure tires and ultimately prevent that. A yellow light should light up in your dashboard as soon as the air pressure in tires reaches a certain threshold, usually 2 to 5 psi under the recommended pressure. Depending on the car manufacturer, the icon could be anything from a tire icon to the TPMS (tire pressure monitoring system) acronym.
When things go bad
Whenever it happens, the first thing to do is to pull over and confirm that one of your tires look like it’s actually under-inflated. If one of the sensors is broken, it could send a false low-pressure signal.
If one of the tires is flat, you need to install spare tires and get your car to an auto repair shop to get it fixed. Or you can also buy a DIY flat repair kit and fix it yourself. But whatever you do, don’t try to drive with a flat tire or you may damage your rim and could also lose control of the vehicle and crash.
If there’s still some air inside, you may have a slow leak. If you thought of keeping a portable inflator in your trunk, simply put more air in the problematic tire and get to the nearest shop as soon as you can. You can still drive for a short distance with a low-pressure tire as long as the tire is not squeezed between the edge of the rim and the pavement. When in doubt, always install your spare tire before going any further.
If all your tires look like they are ok, you could have a sensor problem. Most sensor faults are caused by:
- No communication between the sensor and the TPMS module
- Internal circuit problems
- Broken sensor because of an improper tire mounting technique
A flashing TPMS light usually means that the TPMS unit is not receiving data from one or all sensors. To identify the cause of the problem, you’ll have to get your hands on a professional OBD2 scan tool or a TPMS scan tool with programming capabilities.
Scanning for DTCs
In most cases, when the TPMS light is blinking, it will record a DTC (Diagnostic Trouble Code) in your car’s ECM. Scanning for DTCs could speed up the process as it will give you a good indication of what the problem is, where it’s located and what you should check up first.
For example, a C0750 code (Tire Pressure Monitor (TPM) system sensor not transmitting) will indicate that one of your sensors is not sending anything to the module and your next move should be to inspect and test the sensors. On the contrary, a U0127 code (Lost Communication With Tire Pressure Monitor Module) will indicate a communication problem between the TPMS module and the ECM. In such a situation, you should definitely look for an open circuit between the module and the ECM before suspecting a sensor problem.
Reprogramming the sensors
The easiest thing to try is to reprogram every one of your sensors one by one and see if it’s working again. Wireless devices tend to log out and break the link with the other devices they are paired with for no apparent reasons. Simply think about your wireless speakers, PC printers and other Bluetooth-enabled devices and you’ll understand what I mean. So just try pairing everything together again first before you bring out the big guns to troubleshoot a potentially complicated problem for nothing.
To do that, you’ll either need a professional TPMS tool or a cheap one with teaching functions and the correct procedure to enter your car’s TPMS teaching mode. “Teaching” here means “programming” the sensors. It could also be called “learning mode” or something alike depending on the manufacturer. Be aware of what functions are included for what car brand when you buy a TPMS tool as they don’t all have the same features for all car models and some of them don’t allow the teaching of new sensors.
Every car is different and they all have their own procedure to enter teaching mode. For example, for older GM vehicles, you need to press the LOCK and UNLOCK button on the key fob for 5 sec. or until the horn sounds twice. Ford F-series requires you to press the brake pedal once, push the START button 5 times, press the brake pedal again, and push the START button again 6 times.
Professional TPMS scan tools, on the other hand, can easily record and teach sensors using only the OBD port or a Bluetooth connection so you don’t need to put your car in teaching mode before doing anything. Simply record the sensor signals one by one, plug the TPMS tool in the OBD port and wait for the teaching confirmation.
Identifying a faulty sensor
If even after reprogramming everything you still have an error message in the information center or a blinking TPMS light, one of your sensors is probably faulty and stopped sending any kind of signal back to the unit. To find which sensor needs to be replaced, take out your OBD2 scan tool and go to the “live data” section. Find the TPMS sensor data and look out for any irregularities. Make sure all your tires are correctly inflated first using a hand-held tire gauge. If you are absolutely sure that all your tires are at the correct psi, any incorrect pressure reading of any sensor in the data center will indicate a malfunctioning tire sensor. Remove the tire from the rim, replace the faulty sensor with a new one, reinstall the tire and reprogram all your sensors again.
What about a faulty TPMS module?
If all your sensors’ readings are on-point and they all look like they are in good working condition, the only other possible option is a faulty TPMS unit. But just like in any other troubleshooting situation, when you reach the end of the troubleshooting chart and the only remaining option is to replace the ECM, I strongly suggest you start over and check everything all over again. A broken main unit or module is a rare occurrence and such a diagnosis can easily turn out as a really expensive mistake.
Anybody working on TPMS systems needs to keep in mind and understand that tire pressure systems aren’t standardized like OBD and CAN bus are. Every car manufacturer still has its own way of doing things. Because TPMS are still quite new, they are subject to new features being added, new and more complicated relearn procedure and constant improvement. Always make sure to research and review how the system works on your car before trying to fix anything. Aside than that, tire pressure sensor faults can easily be fixed with a little knowledge, good tools and a lot of practice.