The radios in the tire pressure monitors transmit at frequencies that are significantly lower than the frequency range of Bluetooth radios. Specifically, TPMS monitors transmit at either 315 MHz (USA) or 433 MHz (Europe). In contrast, the Bluetooth frequency range is between 2.402 and 2.48 GHz. That is a substantial separation within the electromagnetic spectrum, so direct wave interference of the signals is not the problem. Possibly magnetic induction in one of the printed circuits of the TPMS module?

 

Bill,

I'm not an electrical engineer or computer guru, but don't all the electronic signals (TPMS, Bluetooth, WiFi, AM/FM, SatNav, drive-by-wire, and whatever other electronic signals there may be) pass through the car's circuitry to illuminate the dashboard warning lights? If so, then isn't there a possibility of an error from a corrupted signal caused by a non-OEM electronic device?

I mention this because several years ago the dashboard on my 2013 XJ went bonkers and lit up like a Christmas tree. To make a long story short, my Service Adviser told me to always unplug my ELM327 device from the OBDII port (that I use with the free Torque app and my old Droid Incredible phone for water and voltage gauges) after I shut off the engine. I haven't had another warning light since then.

Stuart

P.S. I forgot to include the Smartkey...

 

The main reason for that is the OBDII port is permanently live. An ELM327 device can discharge the battery sufficiently to prevent starting when parked at an airport for three weeks.

Graham

 

Some OBDII scanners claim to have an auto-sleep mode that conserves battery levels. For example, the vgate iCar Pro that I have claims to automatically sleep after the car is turned off, and to draw less than 3ma in sleep mode.

 

Again, I don't know the cause but it was too much to be coincidental. I plugged and unplugged the DT dongle more than a dozen times all with the same result. It may have been specific to my car. It made no sense to me either Bill, yet it happened. And as I mention, CeeJay did the same exercise and there was no relation to his OBDII dongle and his dash warning. In any event, Stuart's advice to remove the dongle when shutting down the car is the path I take now and since have the new Tesla screen, I have or will have an entirely different TPMS system.

 

The thing about
TIRE PRESSURE
SYSTEM FAULT
is that it's usually the System, not a wheel sensor. If a single sensor was bad, it would say so.
How about that Frayed Wiring behind the right-side headlight?
That's an easy thing to check, and somewhat common among those with the fault.
Not mine though.
Mine sucks elsewhere.

 

Short answer - yes. Answer that lawyers like - it depends.

Any device that can radiate electromagnetic waves has the potential to interfere with another electronic device through magnetic induction. When the EM waves travel through another device, small electric currents are induced by the fluctuating magnetic field in the signal. That's the theory. In practice, many factors affect whether these induced currents will have any consequences. Among these - the strength of the EM waves at the point of induction (which in turn is determined by the square of the distance between the two circuits and the power output of the transmitting device, as well as radio-opaque or -absorbing materials material between the two), the frequency of the signal, the components in the circuit in which the current is induced and the threshold currents at which something will happen in the induced circuit.

As an example, take the Bluetooth radio in an OBDII scanner. It has an extremely low-power radio, so that outgoing signal is measured in milliwatts. However, it is probably very close to the TPMS module and emits a relatively high-frequency signal. Is there shielding on the TPMS module or its components? If so, the inducing magnetic field might be very weak or non-existent beyond the shielding. And even if a current is induced in the TPMS module, what strength is required to trigger a fault signal?

 

It could have just been that particular dongle. These cheap things are made in China, and do they go through rigorous EMI testing before shipping them? Unlikely. Who knows what spurious frequencies they’re throwing out. Put a spectrum analyzer next to that one, and you may be surprised.

 

so this is behind the plastic wheel well?hmmm i'm afraid to take it off to have a look cause i'm afraid i might damage mine if i do that

 

YES - it is. The liners are a lot easier to remove/replace than on earlier models. Mainly it's M6 x 21mm setscrews.

They spread salt on the roads here at the slightest hint of an overnight frost so I take the liners off for a thorough clean of the wheelarches at the end of Winter.

Graham

 

I've had this issue twice ...

1. When I ran a 12V accessory wire from the rear fuse box to power a bluetooth radio transmitter. So it seems IT IS possible that an aftermarket bluetooth transmitter can interfere with the TPMS sensor/receivers - at least it did in my situation. Removed the bluetooth and wire - problem solved.

2. When the car sat for a few days without the CTEK plugged in. Battery was clearly a bit low and after an overnight charge the fault message went away.

How old is your battery? Surprised no one mentioned battery voltage - the typical culprit for electrical issues, no?

 

Can an indie disable this awful system?

 

they have the capability if they have SDD but whether or not they'll do it is another question.

 

That or put some air in the tires. Worked for me

 

That often proves to be the solution after having a tyre replaced and there is no component fault. A temporary increase in pressure and drive for a few miles resets the warning.

Graham

 

Gee, never thought of that.
Oh, wait, yes I did, like almost two years ago. Before I replaced every single component except for the wiring, which I chased.

 

The thread has a mixture of those who want to fix TPMS and those who don't want it at all.

In order to assist the first group I've added the DTC List and Pinpoint Test sequence from the Workshop Manual to the XK/XKR - 'How To' / DIY Repair & Maintenance sticky at the top of the threads. They are in section 14 - WHEELS / TPMS. The PDF's are too big for forum attachment and the links are to free download from my MediaFire online storage.

Graham

 

Since you increased the tire pressures before you replaced all the components to no avail, try it again and maybe you'll get lucky and the TPMS will work properly.

With the engine off, I'd deflate all 4 tires to 25 lbs. and then start the engine. Hopefully, the TPMS warning will illuminate. Next, shut off the engine, inflate all 4 tires to 45 lbs. and go for a short drive and see what happens. Don't forget to reduce those tire pressures back to normal.

it's worth a try.

 

I would LOVE to have my TPMS work again, but danged if I can figure out what to do next to fix it.

 

Have you run a SDD diagnostics session?

Graham