- If it is Out, it Doesn’t Mean it Will Stay Out
Even if the TPMS light is out when the vehicle leaves the service bay, it does not mean the light will not come on later. Usually, this happens when the customer is driving home. According to NHTSA TPMS rules, once a vehicle is started, it can take up to 20 minutes before the TPMS system activates and is ready to alert the driver there is an inflation problem. The “problem” could be air loss, system errors or a sensor that was damaged, perhaps during a demount/mount. This is why looking up the service procedure is required if you are performing any TPMS work, and you will need to perform a little bit of quality control after the repair.
- Stem Identification
In the past three years, there has been a shift to rubber valve stems by Ford, GM and other carmakers. At first glance, they look just like the valve stems from a non-TPMS vehicle. But, the cap will be longer and the stem will have more threads when compared to a conventional stem. This can help a tech avoid damaging a sensor by accidentally pulling the stem. But regardless of the valve stem’s appearance, every model year 2007 and later vehicle has a TPMS system.
- No More Soap and Water
Obviously, dry air and humid air have different properties. TPMS sensors are calibrated to deal with normal ranges of humidity found in the real world. But, if water is trapped inside the tire, it can change how the pressure relates to temperature. Humidity or the amount of moisture in the atmosphere changes the density of air. Surprisingly, more moisture results in lower air density. At high humidity, the air density inside the tire decreases due to the reduced mass in a given volume. This will cause the TPMS light to come on sooner as the tire cools or heats up. If your shop is using a solution of soap and water to help in the mounting of tires, you could be leaving enough water inside the tire to change how the pressures react under changing temperatures. Use only mounting paste. The price of a small bucket of paste is less than the cost of a comeback.
- Proper Inflation
The inflation pressure shown on the door jamb placard or in the owner’s manual is for cold tires (sitting for at least three hours). If you have a customer who brought their vehicle in for an oil change and is waiting for the service to be completed, you may not have the time necessary to properly inflate and check their tires. You can try adding 2-4 psi to the recommended placard inflation because the tires are hot, and ask the customer to check their inflation pressures the following morning. This can prevent the light from coming on after the tires cool down.
- Spare Moment
Before you start a relearn procedure on TPMS sensors, check to see if the spare tire has a sensor. Often, the service information will make the relearn procedures generic so it can be used for a variety of models. Usually the spare is the last sensor to be tested in a relearn procedure. This can be frustrating because it may seem like the vehicle will not relearn the new positions, when actually it is waiting to get information from the spare.
- Record Sensor IDs
If you are installing new tires with new sensors, it is a good idea to record the sensor ID numbers and positions before the new tires are mounted. Some vehicle makes – including Nissan, Toyota and Honda vehicles – require that the sensor IDs be entered into the TPMS module through the DLC. This can really save time if something goes wrong during the relearn process and a sensor is not showing up in the memory.
- Invest in Training
Training is one of the most important investments you can make. Two key reasons: First, proper training helps your techs to prevent damage to sensors and reduce diagnosis and relearn problems. Second, proper training prevents you from sending a customer to a car dealer, where they could be lost forever. In fact, training will make yours the “go-to” store for TPMS issues, and car dealers will be sending trouble vehicles your way. TPMS is always changing, so constant training updates are required to keep up with new systems and sensors.
- Storage Mode Frustration
Technicians can become frustrated by new sensors stuck in storage or “super sleep” mode. Sensor makers are putting sensors in this mode to increase their shelf life by conserving the battery. Waking up a new sensor may require a rapid deflation or driving. Check the service information or the sensor’s manufacturer information.
- Be Patient
When a relearn process is started, vehicles want only one sensor talking at a time. Sometimes all of the sensors are active and sending out signals because the vehicle was repositioned or there is radio interference. For the sensors to go into a sleep mode, the car has to be still for a set amount of time (which varies from vehicle to vehicle). If you are having a difficult time with a relearn procedure, let the vehicle sit for 20 minutes. This should put the sensors into sleep mode, and then you can turn the sensors on one at a time so the IDs and positions can be read by the TPMS system.
- Chuck the Chuck
If you work on light and heavy vehicles, the long-style air chuck common for larger trucks should not be used on passenger vehicles. These chucks can create enough leverage to bend or break an aluminum stem.
