TPMS & Radio Waves: What You Can't See Can Hold Up a Relearn - AutoSuccessOnline

TPMS & Radio Waves: What You Can’t See Can Hold Up a Relearn

TPMS and keyless entry can be difficult to understand because these systems rely on transmitting, receiving and decoding radio waves. You can see wires connecting modules and components, but seeing radio signals takes a little faith in science.

TPMS and keyless entry can be difficult to understand because these systems rely on transmitting, receiving and decoding radio waves. You can see wires connecting modules and components, but seeing radio signals takes a little faith in science.

Radio waves are a type of electromagnetic radiation that have artificially organized patterns of waves so it transmits information. Still confused? Think of a TPMS sensor; it transmits a very low power signal that goes in all directions. The wave is absorbed and reflected off the vehicle and environment. The antenna on the vehicle, that could be on the windshield, in the wheel well or other locations, receives part of the wave.

TPMS sensor signals are low power and low frequency with the majority of sensors transmitting at 315 MHz or 413 MHz. Keyless entry fobs also operate at this frequency.

The other thing to remember is that similar frequencies in the same area can interfere with each other. In the 315-413 MHz range are a lot of consumer products, like home alarm systems and home automation products like smart light bulbs. In some cases, electronic devices such as phone chargers can emit unintended electromagnetic radiation.

If a TPMS sensor transmitted all the time, a sensor would not last very long. Most TPMS sensors will transmit when movement is detected through a simple accelerometer inside. If the wheel stops moving, the sensor will stop broadcasting after a programmed amount of time. But once it is triggered, the sensor transmits on a predetermined interval set by the manufacturer. A sensor will immediately send a signal if it detects a sudden loss in pressure. A sensor never receives radio signals during normal operation. The only time a sensor receives a signal is when a TPMS tool activates the sensor by emitting an electromagnetic pulse.

The TPMS will not turn the light on if a single transmission is not received; it takes multiple missed signals. The system knows that a missed or garbled transmission might be an external issue like a sensor on another vehicle transmitting at the same time or interference from the sensor being behind a brake caliper. It is like a misfire monitor, it only sets a code if the problem reaches a specific threshold. 

Radio Wave Diagnostic Tips

1. Perform relearns away from other vehicles and sources of electromagnetic interference like alarms and home appliances.

2. If a vehicle can’t receive signals from a sensor during a relearn process, try rolling the vehicle forward a few feet to unblock a sensor.

3. To avoid radio frequency issues, try relearning sensor positions with a TPMS tool that can interface with the TPMS module through the OBD II port.

4. If a sensor can’t be activated with a TPMS tool, try rapidly deflating the tire by pushing in the valve stem. Hold the tool near the tire to see if the tool received the sensor’s ID.

Click here to view more solutions from Andrew Markel.

You May Also Like

Why Do Vehicles Go Out of Alignment?

If camber, caster or toe are out of specifications, there is usually a reason why.

You’ve seen it a hundred times. A vehicle comes in with abnormal wear on a front tire. It looks like camber wear. One shoulder is badly worn, but the other front tire appears to be OK. You put it on your alignment machine and check camber and toe. Sure enough, camber on the wheel with the worn tire is out of specifications. You visually inspect the suspension for obvious signs of wear or damage like collapsed control arm bushings, a bad ball joint, or a weak or broken spring, but you find nothing. You assume the front end is out of adjustment, so you reset camber to specifications and send the customer on his or her way.

Hunter Engineering: ADAS Calibration & Connectivity Drive Growth

Hunter’s Pete Liebetreu explains the company’s Ultimate ADAS system, its areas of growth and its outlook on wheel service for EVs.

Hunter's Pete Liebetreu explains the company's Ultimate ADAS system, its areas of growth and its outlook on wheel service for EVs.
Selecting the Ideal Car Lift for EV Servicing

When choosing the right car lift for servicing electric vehicles there are several key factors to consider.

Key Factors in Selecting the Ideal Car Lift for Electric Vehicle Servicing- Coats
Mayhew Introduces 14-Piece Micro Hand Tool Set

This new set is a compilation of all the current micro line products, including pry bars, picks, hooks and screwdrivers.

This new set is a compilation of all the current micro line products from Mayhew; including pry bars, picks, hooks and screwdrivers.
BendPak Offers Space-Saving Full-Rise Scissor Lift

The new BendPak SP-7XE Series of full-rise scissor lifts provides the performance and undercarriage access of traditional two-post lifts in a more compact, space-saving package.

The new BendPak SP-7XE Series of full-rise scissor lifts provides the performance and undercarriage access of traditional two-post lifts in a more compact, space-saving package. Floor- and flush-mount models of this frame-engaging lift are available.

Other Posts

Hunter Engineering Wins Optimizely Award

Hunter employed several Optimizely products to help provide exceptional customer experiences. With the assistance of Optimizely CMS, Hunter’s corporate website Hunter.com saw a 70% increase in monthly average pageviews.

Hunter Engineering Wins Optimizely Award
Collision Careers Launches Digital Campaign to Attract Technicians

Aimed at attracting technicians to the field, the videos highlight various professional roles in collision repair including structural technicians, estimators and electric diagnostics technicians.

collision careers tech shortage
ASE, Dealer Associations Partner to Increase Awareness of Automotive Careers

ASE is partnering with dealer associations to conduct student competitions designed to increase awareness of automotive career opportunities.

young automotive technicians and mechanics
Access Tight Spaces with Mini Angle Die Grinder

The low-weight, ultra-compact design provides added control and maneuverability.

Florida Pneumatic Manufacturing Corporation recently released the AIRCAT 6250 1⁄4” Mini Angle Die Grinder.