Over Inflated Tires and TPWS Light Issue I've had my Prius C for 600 miles now and I finally checked the tire pressures. Silly me. I expected the dealer would have properly inflated the tires. The fronts were 51/52 psi and the backs were 50/51 psi. No wonder the ride felt so harsh. The maximum listed on the tire is 44 psi. Aggravating, but something I could fix. After I deflated the tires to 40 front and 39 back, I was shocked that the tire pressure warning system light did NOT come on. Does this mean the system was never initialized? Or does this mean the system is broken? Should I be worried? Tom
it actually reads the pressure in the tires themselves and will go off under a certain number... what that number is however... i am unsure of. you should not be worried.
Interesting, the tires on my c3 are goodyears, and the max sidewall is 51, so I just checked them today and took them up to 51 for max mileage. Got 58 mpg on a 61 mile trip into 15-20 mph wind doing avg of 52 mph. 67 mpg the other direction with the tail wind. 3 people in the car, above avg size. This car is a mileage monster!
TPMS reports when tire pressure drops a bit below the setpoint. If your dealer couldn't properly inflate the tires, there is no reason to assume that they reset the TPMS after inflation. It was probably set to factory spec, not the overinflated pressure. Tom
I don't think it can be a fixed number, though, as the owner's manual say to reset the system (by pushing and holding the button under the dash) whenever the tires are rotated front to back. "When to initialize: When rotating the tires on vehicles with differing front and rear tire inflation pressures." And this statement confirms that the low pressure warning level is tied to the tire pressure at the time that the system is initialized: "When initializing the tire pressure warning system: Do not operate the tire pressure warning reset switch without first adjusting the tire inflation pressure to the specified level. Otherwise, the tire pressure warning light may not come on even if the tire inflation pressure is low, or it may come on when the tire inflation pressure is actually normal." Finally, this implies that the low-pressure trip point is quite a long way down: "As an added safety feature, your vehicle has been equipped with a tire pressure monitoring system (TPMS-tire pressure warning system) that illuminates a low tire pressure telltale (tire pressure warning light) when one or more of your tires is significantly under-inflated."
Your post was only two minutes behind mine, so I'll assume you didn't get to read it before posting. The reset button under the steering wheel establishes the setpoint, which is a few psi under the pressure at the time you reset the system. Tom
Correct - your post must have appeared while I was searching the manual for the various references. But since the manual says the light comes on only when a tire is "significantly" underinflated, the setpoint must be quite a bit below the nominal pressure, so the question remains, how far below the setpoint is the warning level? It's low enough that the manual cautions against continuing to drive the car at this point.
The TPMS will trip when 25% of the set pressure is lost. If set at the delivered pressure it would trip at 39psi. You must have gotten my tires. I had to pump mine up to max sidewall pressure. "Aggravating, but something I could fix." It really wasn't aggravating since I expected that I'd have to do it.
Aggravating because I expected the dealer to prep the car better (I had to insist the dealership find and mount the antenna too). Also aggravating because I was so slow to realize why the ride was so danged harsh! Tom
This is the first time I've ever heard of the acronym TPWS. Isn't it referred to in the manual as TPMS?
As I quoted above, the manual for the c has this inconsistent statement: "As an added safety feature, your vehicle has been equipped with a tire pressure monitoring system (TPMS-tire pressure warning system) that illuminates a low tire pressure telltale (tire pressure warning light) when one or more of your tires is significantly under-inflated."
TPMS is the monitoring system; in other words it monitors the tire pressure. The warning system warns the driver of a problem. In this case the warning system is the idiot light. Tom
I keep all my tires inflated to max sidewall pressure which for my tires are 44 psi. I have over 61,000 miles and they are wearing even.
