Tire Pressure Monitor System

Not sure if this helps but when the dealer was repairing a tire on our 2016 MKC the phone app issued a warning of low pressure being detected. So that would tell me it is direct. Now the MKC system may be looking for a fault indication from a sensor as opposed to the presence of a continual signal from a sensor. So the absence of a sensor may not trigger a light but you now have a vehicle designed with a LPWS that will never indicate a fault when/if your tires go low.

An indirect TPMS typically relies on wheel speed sensors that the anti-lock brake system uses. These sensors measure the rate of revolution each wheel is making and can be used by on-board computer systems to compare with each other and to other vehicle operation data such as speed.
Based on the rate of revolution of each wheel, the computer can interpret the relative size of the tires on your vehicle. When a wheel starts spinning faster than expected, the computer calculates that the tire is underinflated and alert the driver accordingly.
So, an indirect tire pressure monitoring system doesn’t actually measure tire pressure. It’s not electronically processing the same kind of measurement you might see with a tire gauge. Instead, an indirect tire pressure monitor simply measures how fast your tires are rotating and sends signals to the computer that will actuate the indicator light when something in the rotation seems amiss.

The following is the response that the service manager received from Ford. So the system is direct and since I did not have sensors installed on the winter tires I purchased, and the low pressure indicator light is not on, I can only conclude that there is something wrong with the TPMS system in my car.

Although it is possible that the TPMS light is inoperative, it is not likely that there is a fault with the TPMS light. As outlined in the online Workshop Manual (WSM) Section 204-04B Tire Pressure Monitoring System (TPMS) > Description and Operation > Tire Pressure Monitoring System (TPMS) – System Operation and Component Description, if the tire pressure deviates from the programmed tire pressure the Body Control Module (BCM), using the MS-CAN, signals the Instrument Panel Cluster (IPC) to illuminate the TPMS warning indicator and display a message in the message center.

Since neither the TPMS light nor the TPMS warning message are not being illuminated/displayed, it is possible that new TPMS sensors were installed when the customer had the winter wheels and tires installed on the vehicle. To verify that there are TPMS sensors, please proceed with previous recommendations of monitoring the TPMS_STAT PID, as well as the TPM_S_ID_LF, TPM_S_ID_RF, TPM_S_ID_LRO, and the TPM_S_ID_RRO PIDs.

If it has been determined that there are not TPMS sensors installed on the vehicle, it is recommended to perform Pinpoint Test (PPT) R located in the WSM Section 413-01 Instrumentation, Message Center and Warning Chimes > Diagnosis and Testing > Instrumentation, Message Center and Warning Chimes. This test is intended to diagnose low tire pressure, communication concerns, GWM, BCM, TPMS, and IPC concerns.



If it is proven 100% there are no sensors then the vehicle would require further diagnostic as to why the light is not coming on.

I have had TPMS on several vehicles with no sensors in the winter tires:

- 2001 & 2004 Toyota Solara - warning light stayed on continuously
- 2008 Lexus IS250 - indirect system, no indicator light
- 2012 Toyota Venza - warning light stayed on continuously
- 2015 MKC - warning light is OFF majority of the time but comes on occasionally after driving 25-30 km. The light will then come on no matter how many times the vehicle is stopped/started the same day. When the vehicle is started the next day, the light is off and stays off unless I drove another 25-30 km.

Most vehicles sold in Canada now have TPMS although not required by law. According to both Ford and Lincoln, the warning light should be on continuously in my MKC and they have no idea why it is not. They have done several diagnostic tests and cannot find anything wrong. It does not give me a lot of confidence when they can't determine the problem. The service advisor drives a Ford (not sure what model) and says the light is on continuously when the winter tires with no sensors are installed.

I have been reading up about TPMS systems to determine if I should get winter tires with them. My theory is this:

• The TPMS sensors have to be mated with the vehicle so it knows which ones to communicate with.
• If your winter tires have TPMS sensors installed then each set has to be mated with the vehicle at the seasonal tire changes.
• Since your winter tires have no TPMS sensors the all-seasons are still mated with the vehicle.
• When you start your vehicle it transmits a signal to the sensors to send tire pressure status.
• The sensors do not transmit data continuously (to preserve the life of the embedded battery) but perhaps only once per minute after they are wakened - ie when the vehicle is started.
• Since in normal operation there may be interference with reception of the signals from the sensors the vehicle module waits for a while to see if there are valid signals before determining there is a fault.

It would appear that TPMS would determine all is OK when you start the vehicle in proximity to your tires with the sensors and then determine there is a fault after you have driven away from them for a while. Does this make sense?

Countryguy:

Actually, I am an Electrical Engineer - worked in the power field for close to 40 years as well as doing a number of electronic and microcontroller projects on my own. I believe you are an IT guy so this should make some sense.

The sensors use microcontrollers to process the data. Suppose the microcontroller used has a 4 MHz clock (relatively slow by today's standards) and needs four clock cycles per instruction, it can process a million instructions a second. I doubt there would need to be more than a few hundred instructions each time it transmits - probably less than a millisecond of actual processing. The microcontroller can be programmed to go into sleep mode with only a slow clock running and then after a set amount of time wake up and process data. The power consumption in sleep mode is very low and that is what preserves the battery life.

By the way, I have just ordered a 2017 MKC Reserve for delivery late March or early April. After all this discussion and research, I am convinced that I should get winter tires and wheels without TPMS sensors in the fall and put up with the alarm. My son and I can look after the seasonal tire changes and we won't have to worry about going back to the dealership to have this done and the sensors re-linked to the vehicle.