The low air alert came on the morning after I went over an unmarked depression in the road at night, caused byroad construction. It really jostled my car. I'm wondering if somehow this could have caused the tire sensor to go out of whack? I tested the air on my tires and only found one that showed low air. Put in some more air at the station. now all the tires seem to be in the same range: 29-30, but the low air alert remains on in my car. would appreciate any suggestions about the probable cause and best way to proceed! Also any suggestions about the best way to monitor air in tires to make sure they are all in the right range? I find the manual gauges hard to use, and don't have much confidence in them. Saw a digital monitor on Amazon, which I'm thinking might be more convenient and accurate - anyone used one of these?
You can fairly easily test the OEM monitors to be sure they are working and then don't worry about it. The pressure will not go UP on it's own enough to cause a problem. Digital tire gauges are good.....in my experience and you don't have to pay a lot. Is that what you mean by a digital "monitor" ? IF.....30 is the right pressure, there likely is a simple procedure to "reset" the system for the present pressure. If that fails, you need help from a dealer or tire shop. IF.....you really have a 2010 model car like your profile says, the sensors might indeed be going bad and might ALL need to be replaced to be reliable.
Its normal for the warning to stay lit for a while, you need to drive the car a ways for it to reset.
15” are 35/33 front/rear if I’m not mistaken. Air em all up to 36, see what happens? Is your gauge accurate too? Try another just for giggles. also, once set where you like, do the TPMS reset* will reestablish the baseline pressure, what the computers expect pressure to be. Then they should only alert with something like 25% drop. * Explained in Owner’s Manual
Normal? That "a while" should be measured in seconds to a couple minutes, once the pressure is corrected, or proper TPMS codes programmed in after a swap. Provided the sensor battery is not dead. And 29-30 psi is not an adequate pressure for this car. For OP's 2010-III, it should be at least 35 front / 33 rear with the OEM tire size, or slightly less if the tires were upsized.
The system has some hysteresis built in, so once the light comes on (which doesn't happen until several psi below the set pressure, too low for my comfort), it won't go back out in seconds to a couple minutes unless the pressure was raised again, also by several psi. It might work out ok that way for most folks who use it the way Toyota envisioned. Me, I don't like having the light only come on at twenty-something psi, that's way too low. So on my car, I once pumped all the tires up to the sidewall max, and pressed the TPMS set button there, and then lowered the pressures back to what I really want. That way, the warning light comes on when they're just a couple psi low. The downside of that is, yes, for me I sometimes do have to wait for a substantial drive before the light goes back out. (Or I can deliberately overinflate, watch for the light to go out, then let back down to my pressure. That's what I was doing regularly with a slow leak I discovered in March and put off getting fixed until 2 weeks post-vax.)
I found one freely available (new vehicle) PreDelivery Service (PDS) bulletin here: https://static.nhtsa.gov/odi/tsbs/2016/MC-10132883-9999.pdf And it includes TPWS* calibration. So when you here the reports here, by new owners, that they found their tires at 45~50 psi, guess that’s another goof off dealership. * TPWS standing for Tire Pressure Warning System (I’m confused; doesn’t Toyota also say TPMS, Tire Pressure Monitoring System??) anyway yeah, cars leave factory with tire pressures at max sidewall pressure, and dealership was SUPPOSED to drop the pressures to spec and then calibrate the system. addendum: Interesting point made here: Rubber plugs installed at pre-delivery inspection? | PriusChat that if dealership charges the customer for PDS, and is reimbursed by Toyota, but doesn’t perform some or all of the services, that amounts to fraud.
Thanks, yes, found the sticker - 33 - 35 - that's the right range! First website I consulted had wrong info, saying all tires should be around 30. Well, at least now I know what to do. Have also ordered a digital guage, so once I receive it, it's back to the station I go!
Any reasonable warning system built on analog measurements should have some hysteresis built in, to prevent flickering or bouncing from measurement noise. Were you dealing with threshold cases, where the pressure was only barely tripping the alert, then depending at least partly on "highway warmup" to get back above the alert threshold? The tire warmup process, which does raise pressure by several psi, will take some significant time. I don't have first hand experience with that sort of TPMS event. Most of mine been caused by forgetting to reprogram IDs while swapping seasonal tire sets, and these alerts have cleared very quickly after getting the right codes in. The other non-flat episodes seem to have been spurious cases where the car's TPMS receiver didn't receive the transmissions from a single sensor for a too-long period (similar to dead batteries), so lit up the warning based on lack of signal for a certain period. At least this is my best diagnosis after updating a ScanGauge-II to show individual tire pressures. When the radio receiver finally recognized a new signal, 5 to 15 minutes after the warning light lit up, the light would turn off at about the same moment that a fresh valid pressure reading appeared on the ScanGauge. As for the intended TPMS function, apart from the spurious alerts, my Prius and Subaru have correctly alerted on two events each of tires actually going flat. Two were slow leaks, one medium speed, and one fairly rapid.
