Tire Pressure Monitoring Light Flashing

About once a week the tire pressure warning light on my car will turn on and flash for about 60 seconds before staying on continuously for some period of time. I check the tire pressure and it is always around 38 psi. The car is almost 2 months old, has just over 7000 miles on it and has never had any tire related problems. The owner's manual and internet sources state that flashing for 60 seconds and then illuminating continuously indicate a malfunction and I should have the system checked by the dealer. Today I did just that. The dealer adjusted the tire pressure to 35 front and 33 rear and reset the system. They said that was all they could do since the light wasn’t on when I brought it in.

Are there any additional steps that can be performed to help diagnose this? I know there are error codes associated with faults in the TPMS. Are these error codes stored so a properly trained technician can review them later?

 

That has been tried but the problem still persists.

I don't think the TPMS is reporting a problem with the tire pressure.

To quote the manual:
"When the light stays on after blinking for 1 minute: Malfunction in the tire pressure warning system. Have the system checked by your Toyota dealer."

The light is indicating some type of problem with the system. However the dealership was packed and seemed more interested in getting me back out the door than actually diagnosing the problem. That's why I'm searching for information here.

 

No bluetooth or wireless in the area of the trunk. There usually is a cell phone with bluetooth in the center console.

There is a 10" subwoofer with class D amplifier tucked into the storage area of the hatch on the driver's side. Anybody ever have interference issues between the TPMS and a sub/amp?

 

After doing some more research I discovered that the error codes are stored. (Why couldn't the dealership pull these up??? Maybe I need to find a different dealership.)

It is possible to recall these codes by grounding pin 13 of the DLC3 connector and turning the ignition on. The TPMS light will flash the stored error codes. My prius is reporting a 23 and a 24. These error codes correspond with "No Signal from Transmitter ID3 in Main Mode" and "No Signal from Transmitter ID4 in Main Mode"

 

Thanks for all the help and suggestions so far.

For a little more background information. The amp and sub are a matched set from an MTX Thunderform enclosure. The sub has an impedance of around 0.38 ohms. The amplifier is mounted inside the custom fiberglass enclosure. Output wires were kept to a minimum length(maybe 10 inches). The amplifier actually does not have a DC/DC converter to step up the voltage. The output stage has four discrete transistors (probably MOSFETs) in an H-Drive configuration to a 12 volt bus. The 12 volt bus is filtered. I can recall an inductor and multiple capacitors for this purpose. The output was filtered too. I believe there were three inductors, probably some capacitors too.

I've contacted MTX about this and am waiting a response. If it truly is the amplifier, hopefully they will already know the solution.