Don't get caught out by TPMS!

5 October 2017

Repairing or at least servicing vehicles with Tyre Pressure Monitoring Systems (or TPMS) may be common place for dealership technicians today, but that may not be the case for many of our members in independent and franchise workshops.

For that reason, we’re going to take a look at some of the common issues you may encounter as well as some tips to avoid making some mistakes!

Let’s first establish a couple of important facts about the requirements of a TPMS:

• A sensor MUST instantly report a low pressure condition.

• A sensor MUST NOT instantly report an internal fault or flat battery.

 

Ever since you rotated my tyres...

Run this hypothetical situation through your head:

Customer presents to your workshop for a tyre rotation. Vehicle has a faulty TPMS sensor but there is no TPMS warning light on the instrument cluster. You carry out a tyre rotation and your customer calls you half an hour later advising that ever since you carried out the tyre rotation, there is a TPMS light on their instrument cluster.

The end result is going to be a dissatisfied customer or the workshop wearing the cost of the sensor.

Had the sensors been checked prior to performing work, this situation could have been avoided.

So by now you can understand why it’s good practice to routinely check TPMS on vehicles to avoid ‘adopting’ problems. It’s becoming common-place for workshops to carry out system scans on vehicles prior to commencing work (at which point any TPMS DTC’s should be discovered) which help prevents these types of issues and can even help with upselling other repairs. At a bare minimum it is cheap insurance to run over the vehicle with a TPMS Activation/Reset tool to check sensor functionality.

 

Modifying Vehicles

The other consideration to be taken into account when it comes to modifying a vehicle's tyres and/or wheels is that the TPMS works on the nominal inflation pressure of the factory wheels and tyres. Changes to this configuration that result in a significantly different tyre pressure will cause issues with the TPMS.

Most TPMS warning lights will trigger when any tyre reaches 75% of the nominal inflation pressure. To rectify this undesirable behaviour, a suitable scan tool is required to make changes to the TPMS settings.

 

Programming, Relearning & Resetting

These are terms that seem to be used interchangeably when it comes to TPMS when in actual fact they are not all one of the same.

• Some brands of sensors are sold ‘blank’ and require Programming. This tells the sensor what it is and what it needs to do by assigning an ID and Protocol.
• A Relearn is the procedure that needs to be carried out whenever a sensor is moved or replaced so the vehicle knows the position of the sensor in relation to the respective corner of the vehicle (or spare in some instances).
• A Reset procedure usually refers to an ‘Indirect system’ that uses the ABS wheel speed sensors to differentiate tyre diameter changes based on inflation. Resetting this type of system generally requires pressing a button or carrying out an in-vehicle procedure that calibrates while the vehicle is driven.

10 Top Tips for Techs

• If you’re attempting to program a sensor and the process is failing repeatedly, something is wrong. Maybe the procedure you are using to program the sensor is incorrect or maybe there has been a recall on the vehicle that is preventing the TPMS from programming. (This is not unheard of for FCA vehicles) Also, don’t assume the procedure is the same between vehicles within a certain make or model family as the systems can often vary and have different characteristics.

• Don’t forget the spare! Some vehicles (Namely Toyota) have a sensor fitted in the spare tyre. Don’t overlook this when attempting to diagnose TPMS lights and error codes as this is not an uncommon cause of a TPMS light.

• Always be sure to check the torque specification when installing a TPMS sensor and use a torque wrench  to avoid causing damage to the sensor by over or under tightening.

• When one sensor on a vehicle goes bad due to battery failure, it is worth considering replacement of all sensors on the vehicle to avoid inconveniencing the customer as subsequent failures are likely. The lithium battery life in a TPMS sensor is approximately 10 years.

• Approximately ? of vehicles on the road will Auto-Reset after an anomaly with tyre pressure. The remaining ? will need to go through a stationary procedure in the vehicle or with a scan tool.

• Sensors will be marked with a frequency band identification. Make sure that when replacing a sensor the frequency band on the new sensor is the same as the sensor being replaced.

• When carrying out re-learn procedures on TPMS, be sure that no other sensors are within proximity of the vehicle being re-learned (loose wheels or vehicles)

• Always use plastic valve caps on TPMS sensor valves. Using a ferrous metal cap may cause signal interference.

• A solid TPMS MIL (Malfunction Indicator Light) generally indicates that there is a pressure issue with one or more tyres. A flashing TPMS MIL generally indicates that there is a fault with the TMPS system.

• Never use a leak sealing compound like tyre-foam or tyre-slime to repair a leak as these materials may block and contaminate the valve.