So I finally figured out what was causing my seemingly random "TPMS inactive" error codes on my 997.

A bit of background: About 6 weeks ago my TPMS starting acting up - showing problems from 2 of the wheel sensors. I have seen this before in my Cayman, and would let it re-learn and the error would go away. This time, however, it persisted. This car is an 07 C2S so I figured the batteries in the sensors were about done.

I booked an appt and had 3 of the wheel sensors replaced. The forth had been replaced about 8 months ago, so I effectively had all new sensors. All was good. And as I sometimes do with electronic parts, I asked the shop to return to “old” parts to me. Do you see where this is going?

I only drive the car about one or 2 days a week, so I haven’t logged many miles since the repair. However, I have driven it to work the past 3 Fridays and each time, about 10 miles into the drive, it would throw the “TPMS inactive” code again.

However, if I took the car for a wash or errand on the weekend, the error would clear. I never made the correlation of when I had error codes vs. when it cleared.

Figuring the problem must be with the TPMS computer itself, I tried to book an appt at the shop today that did the original repair, but couldn’t get an appt until next week due to the holiday.

Fast forward to this afternoon, driving home from work, with the “!” in my face, and a new message pops up; “Too many wh. Transm.”

WTH? Why would there be too many sensors? Then I thought back to my old parts, looked in my work computer bag sitting on the passenger seat, and lo and behold there were the old sensors buried at the bottom of it. I guess I had tossed the old sensors in my bag weeks ago and forgot about them. No wonder the computer was confused; it was seeing 7 wheels!

Once I removed the sensors from my bag all is well again.

I kinda wondered how this actually worked; I had assumed the shop used the computer to “marry” each sensor to the wheel location based on a unique SN, and it would ignore others, but maybe that’s not how it works. Thinking about it, I guess that wouldn’t be a good design as it would require those who swap wheels frequently to reprogram each time…

Anyway, mystery solved!

 

don'tcha love it when that little light goes on and things come clear...? I know I do, cool,

 

when I change from winter to summer tires and wheels on my DD I have to get the set that is coming off out of the garage before I can get the car to see the new sensors.

 

Shop just installs them in the wheels. Cars system does the rest when you actuat the TPMS reset program. As for the multiple sensor readings, at least one of them is still functioning.

 

Yes. Yes I do see where this is going.... <face-palm>

Though my initial guess was the sensors were on the floor and rolled under the seats or you tossed them into the glove box.. and in both cases forgot about them. Meanwhile your car is doing its best Han Solo... "Its not may fault!"