The recommended pressures shown in the drivers door jamb of my EX are 35 psi front and 33 psi rear . I use these. Using 33 psi on all four may be near enough to be safe but why not use what the manufacturers recommend? The system 'learns' if they are different during the initialisation process.
Tyres can loose about 1 psi or so a month due to air permeating through the rubber , and also tyre pressure drops in colder weather because cold air is denser and takes up less space in the tyre. So dropping from 33 psi to 29 psi is not unexpected. Actually the monitoring system might not even detect this drop as its equal all round. . It normally detects if one wheel is rotating at a different speed to the others because the tyre is going flat. So its still important to regularly check the actual tyre pressure. If the fronts drop from 35psi to 29 psi but the rears from only 33 to 29 psi over the same period you might need to keep an eye on them. But there may not be a problem. Tyre pressure gauges are not always 100% accurate or consistent to the nearest psi. But if just one tyre is losing noticeable pressure....
Sometimes I can top up all four tyre pressures equally ( or even change to my other set of wheels and tyres ) and not need to re initialise the system. But if one tyre is inadvertently adjusted to a slightly different pressure to its partners the system might activate,
The system does sometimes activate shortly after you fit new tyres (or on a brand new car with its new tyres) because the tyres can take time to settle down and bed in to the wheel rims. You might even have to reset it a couple of times before it settles down. Its possible that if all four tyres become equally underinflated over time they might start to 'squirm' more on the rims and activate the system for the same reason.
