Giammalvo Files
Mark Giammalvo

Mark Giammalvo specializes in driveability diagnostics at his family business, Sam Giammalvo's Auto Sales & Service, Inc. in New Bedford, MA.   

Mark, who has been with the business for over 20 years, is an ASE  Master Technician and Parts Specialist. He also holds the ASE L1 certification, and has an associates degree in business management.
Mark is also a writer for Motor Age Magazine and is the past secretary of the Alliance of Automotive Service Professionals, (AASP).

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Another Item I Probably
Won't Be Able To Repair

(Printed in the Journal of The Alliance of Automotive Service Providers, AASP) 

I'm sure that above statement has been uttered often over the past 20 years in this ever changing and advancing automotive service industry.

Undoubtably, onboard vehicle electronics systems have been taking quantum leaps foreword in technology. Unfortunately, these leaps are far ahead of the necessary shop tooling and training needed to repair and diagnose these systems.

This week my brother gave me a copy of an article published in a newsletter put out by one of the technical hotline companies that we do business with. That article was an interesting, but sobering eye opener on some of the latest Low Tire Pressure Warning Systems, (LTPWS). These systems started several years ago when the National Highway and Transportation Safety Administration, (NHTSA), mandated their gradual phase-in for consumer safety. These systems watch tire pressure at all wheels and illuminate a warning lamp when the pressure of one or more tires fall below a certain threshold.

Many of these early systems that you may have encountered are "in direct" systems, in that, actual tire pressure is not directly measured. In these indirect systems, tire pressure is mathematically extrapolated from another vehicle system. Many of these systems can extrapolate this data from the Anti-lock brake system, (ABS), via the wheel speed sensors.

A vehicle with ABS is already measuring the speed at each wheel by watching a tooth ring on each hub through a pulse sensor. With some added mathematics, the waveform of the sensor can be read and watched over time to determine a tire that has low pressure. A tire with low pressure will exhibit a different ratio of turns compared to other tires on the car that have normal pressure.

The best part about these systems is that they do not rely on expensive pressure sensors inside the wheels. Newer cars, with direct systems, now have actual pressure sensors and much care must be taken when mounting and dismounting the tires.

The indirect systems typically have a reset button on the dash that you can push after rotating the tires on a customer's car. This reset tells the LTPWS to clear the "monitor data" in memory. This needs to be done after tire rotation otherwise the LTPWS lamp will be inadvertently illuminated since the system will see that all four tires suddenly have different readings.

The newer vehicles, with the tire pressure sensors, are much more accurate and quicker to respond to low pressures than the older indirect systems. The problem that non-dealership service facilities are going to experience is the lack of ability in being able to reset some of these systems.

This is where the hotline article became very interesting. The author of the article was explaining the operation of the LTPWS on a 2004 Nissan Quest. The Quest uses the newer system of pressure sensors mounted in each wheel that wirelessly transmit each tires pressure to the vehicle's keyless entry receiver.  This system presumes that the left front tire is always on the left front of the car, and the right front tire is always on the right front of the car and so fourth.

After rotating tires on these vehicles, the installer should "initialize" the pressure sensors. In other words the system must "relearn" the new position of each tire pressure sensor. Now that the wheels have changed location, the system needs to be told where each sensor now is. Unfortunately, only the Nissan Consult Tool can reset this system.

Rotating the wheels on this model without resetting the system will not cause the warning light to come on. However, when a low tire is sensed in the future, the system will be warning the driver with the wrong information. Simply stated, if the right front tire is low, the system will advise: "Low pressure at right front tire." If the tires were rotated and the reset was not performed, then is the right front tire now on the left front, right rear, or where? This is why the system must be reset to reacquire each transmitter's new location.

Common sense would dictate that Nissan should have had designed a simple switch that would have made it easier for all technicians to reset this system. Then again, some would say it's just another example of locking out more and more non-dealership shops and technicians.

Just another example of how difficult automobile diagnostics and repair continues to be.


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