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My Toyo 37s; a low one is what set off the Tire Fill Alert turn signal
A while back I walked up to my white 2021 Silverado 2500HD and one rear turn signal was blinking all by itself. My truck has a couple of electrical gremlins already, so I figured this was another one. I started thinking about chafed wires from the lift and a bad switch.
Nope. It was a low tire. My truck has a feature called Tire Fill Alert, and I had no idea it did that. It uses the turn signal at that corner to tell you which tire needs attention. It’s one of my favorite “hidden” features now, and it works great with the big 37×12.50R20 Toyo Open Country R/T Trails on my truck.
Here’s how it works, straight from GM’s owner’s manual, and how to use it.
What Tire Fill Alert Is
According to the 2021 Silverado 2500HD/3500HD owner’s manual, Tire Fill Alert (if equipped) “provides visual and audible alerts outside the vehicle to help when inflating an underinflated tire to the recommended cold tire pressure” (>2021 owner’s manual, p. 345). GM’s official 2022 Silverado HD manual describes it the same way (>2022 Silverado 2500HD/3500HD owner’s manual, PDF).
It works through the Tire Pressure Monitor System (TPMS). Each wheel has a sensor that transmits pressure readings to the truck, so the truck knows which corner is low and which corner’s air pressure is changing.
The visual cue is the turn signal at the tire’s corner. The manual describes the blinker flashing while you add air to that tire. In my case, the corner with the low tire was the one blinking. Owners on GM-Trucks.com describe the same “random” flashing that turned out to be a low tire (>GM-Trucks forum).
How to Use Tire Fill Alert (Step by Step)
The manual’s procedure, for when the low tire pressure light comes on:
Park on a safe, level spot.
Set the parking brake firmly.
Put the truck in P (Park).
Add air to the low tire. The turn signal at that corner flashes while you fill.
When the tire reaches the recommended pressure, the horn sounds once, and the turn signal stops flashing and briefly turns solid.
Repeat for any other low tires.
If you overfill: If a tire goes more than 35 kPa (5 psi) over, the horn sounds multiple times and the signal keeps flashing for several seconds after you stop. While it’s still flashing, briefly press the center of the valve stem to let air out until the horn sounds once (>2021 owner’s manual, p. 345).
No gauge needed, though I still keep one in the truck (see below).
When Tire Fill Alert Won’t Work
The manual lists the situations where it won’t respond properly:
The turn signal doesn’t flash within 15 seconds of starting to inflate (meaning it isn’t activated or isn’t working).
The hazard flashers are on, which interferes with the visual feedback.
Interference from an external device or transmitter. GM’s fix is to move the truck about 3 feet (1 m) forward or back and try again.
The air source doesn’t have enough pressure to inflate the tire.
A TPMS malfunction, a sensor that isn’t registered to the truck, a sensor with a low battery, or a problem with the horn or turn signal lamps.
Check pressures monthly, cold. “Cold” means the truck hasn’t been driven for at least three hours, or for no more than 1 mile.
Cold mornings can trigger the light. The low-pressure light may come on in cool weather and then go off as you drive. GM calls that an early sign the tires need air.
A flashing TPMS light is different. If the light flashes for about a minute and then stays on, the system has a malfunction, not just low pressure. Causes include a missing or damaged sensor, a skipped sensor-matching step after a rotation, or replacement wheels/tires that keep the TPMS from working properly.
Rotate, then relearn. After a tire rotation or sensor replacement, the sensors must be matched to their new positions with a TPMS relearn tool in this order: driver front, passenger front, passenger rear, driver rear.
The spare has no sensor, so swapping it on will trigger the malfunction warning until the road tire goes back on.
Use GM-approved valve caps and tire sealant. The manual warns that the wrong ones can damage the sensors, and that damage isn’t covered by warranty.
A note for lifted trucks on big tires: The manual ties Tire Fill Alert to the recommended cold pressure on the truck’s Tire and Loading Information label. It also says that if your tires are a different size from the label, you should determine the proper pressure for those tires. If you run aftermarket 35s or 37s at a different pressure than the door label, the alert’s “correct pressure” target may not match what you actually want. Ask your tire shop or dealer what’s right for your setup.
My Toyos are Load Range E tires with a 65 psi max per Tiresize.com (>Tiresize.com). If you run E-rated tires, pick an inflator that can easily reach the pressure you run. Never exceed the max on the sidewall.
Why is my Silverado 2500HD turn signal blinking by itself while parked?
Often it’s Tire Fill Alert reacting to a low tire or a change in pressure at that corner. Check that tire’s pressure first. If everything is fine, then look at wiring or the turn signal switch.
Does every Silverado/Sierra HD have Tire Fill Alert?
The owner’s manual lists it as “if equipped,” so check your truck’s manual or try it: if the signal flashes within 15 seconds of adding air, you have it. My 2021 2500HD has it.
Why does my horn honk several times when I’m filling a tire?
That means the tire is more than 5 psi over the recommended pressure. Briefly press the valve stem center while the signal is still flashing to let air out.
Why won’t Tire Fill Alert work?
The usual reasons are hazard flashers on, radio interference (move the truck about 3 feet), an air source that’s too weak, or a TPMS sensor problem.
Do I need a TPMS tool after rotating tires?
Yes, per the owner’s manual. Use a relearn tool in this order: driver front, passenger front, passenger rear, driver rear.
Sources: 2021 and 2022 Chevrolet Silverado 2500HD/3500HD owner’s manuals (GM), linked above. Features vary by trim and options; check your own manual.
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