TPMS malfunction
 

The tire pressure symbol first flashes, and then remains solid; which according to the manual, indicates a malfunction.
All of the tires are of the same size, but not of the same make. Could this be the cause? I am trying to solve this rather than than have the dealer charge me $99.50 just to check it out.

The system doesn't care what size or brand the tires are. It can only measure the pressure in the tire and report it to the system. If it's too low, it causes the indicator light to come on. First, make sure all your tires have proper pressure. If that's not an issue, then the most likely source of a problem is one of the senders in a tire. It could have a dead battery or maybe some other problem. Most good quality tire stores are capable of tracking down the problem. Repairing a sensor requires removal of the tire from the rim, so a tire store is a good place to start.

Thanks