TPS weirdness

[flydutch]

On my 2017 FFH Titanium, I removed the left front wheel/tire assembly to have a rim bend repaired.  I replaced it with the left rear wheel/tire assembly and installed the temporary spare on the left rear position.

When driving the car to deliver the wheel to the repair shop,  I expected the TPS warning system to squawk right away, but it did not.  The TPS graphic actually showed four, well inflated telltales.  Coming to a stop after pulling off the interstate, the TPS fault system finally piped up and displayed the left front data as missing (- - -) but continued to display pressure data from the left rear, where the temp spare is (does not have a TPS sensor, as far as I know - besides, it's inflated to 60 psi, and the telltale shows 34 psi).

Anyone have any ideas as to why the TPS is behaving this way?  Just curious.  It has always reflected very accurate PSI data and any inflation or deflation action I take on each individual tire.

[2014FordFusionSE]

I don't have this feature but if I had to guess, each tire's TPMS is pre-programmed to its location eg. LR for Left Rear.

Since you moved the tire from the left rear to the left front, the car does not know that. It's displaying the air pressure from the left rear tire, thinking it's still in its original location.

[Waldo]

You have to understand that the TPMS sensors only send out a ping of data once every 2 minutes or so (unless there's a dramatic change in pressure, then it sends out immediately).  So no surprise it didn't react right away, especially if you're carrying the wheel with the 4th sensor in the car.   I'm not quite sure how it triangulates where each sensor is , but I know it takes quite a few of the 2 minutes cycles for it to be sure that you've actually rotated your tires. 

[flydutch]

Thank you for your replies.

The backstory on the bent wheel - at some unremembered point, we must have hit a pothole just right with (I surmise) the right front wheel/tire.  On the next tire rotation, that wheel was moved to the left rear (I use a modified cross rotation).  Then, for several thousand miles I noticed an increasingly noticeable "zoom-zoom-zoom' noise coming from the rear of the car.  I believed it was a worn wheel bearing, and merrily DIY replaced two wheel hubs (and brakes) on both rears (the car had 66,000 miles).  Much to my surprise, that job done, "zoom-zoom" was still there.  I rotated the wheels front to back (inspecting each carefully - didn't see any damage or deformation) and lo-and-behold:  "zoom-zoom" moved to the front.  Definitely front left.  Fearing a damaged belt, I took the car to a tire shop and had them inspect the tire; they removed the wheel and spun it on the balancing machine - and discovered a slightly bent wheel, on the inside of the rim.  Hopefully, the rim repair will have now eliminated the noise!  Will report back.

Update:  wheel repair has reduced the noise considerably, though it is still there.  Likely many thousand miles with the bad wheel has patterned the remaining tire tread to make a similar noise.  Still better, though.

Edited January 12 by flydutch

[billford]

FYI,

after changing tire positions, rotating tires, the system needs to be retrained using a tire training tool, otherwise the dashboard display will be incorrect.

If there is no pressure display on the dashboard,  training is not necessary. 

 

Example:

On my 2014, there is no display. If my tire light is on, I don't know what tire is low unless I check all of them. 

 

On later models with the display, if the tire light is on, you know exactly which tire is low, if they are properly trained. If they are not trained, you have to check all of them. 

 

[MeeLee]

My experience is that when rotating the tires (fronts on back and reverse), the tpms is able to auto learn the new position.

But as soon as 2 sensors went bad on my car (the rears), the car kept giving blank data on the front tires, even after rotation.

 

I'm keeping the fronts on the front for now, in hopes they will wear out faster, so I can replace the tpms sensors when the tires need changing.