Quick Summary:
- Confirm whether you have a sealant canister, compressor, or both.
- Call for help if sidewall damage, large holes, or low pressure persists.
- Avoid sealant if the car has TPMS, unless instructed.
- Photograph tyre, wheel, warning lights, and kit contents before any action.
Many modern cars in California no longer carry a full-size spare. Instead, your car hire may include a small 12V compressor, a tyre sealant canister, or a combined “mobility kit”. These kits can be useful, but they also carry risks, especially when the puncture is not a simple tread nail or when the car has a tyre pressure monitoring system (TPMS) sensor inside the wheel.
This guide walks you through how to confirm what kit you actually have, when using sealant can ruin a tyre or TPMS, and exactly what to photograph and report so you can show you acted responsibly and avoid surprise charges later.
First, check what you have in the boot
Before you do anything, park safely and assess the situation. Move well away from traffic, put the car in Park, apply the parking brake, and switch on hazards. In California, breakdown conditions can change quickly on freeway shoulders, so if you are not safely off the road, the best decision is usually to call for help rather than attempt a repair.
Then confirm the kit type. Look in the boot, under the boot floor, or in a side cubby. You are typically looking for one of these:
1) Compressor only. A small inflator with a hose and a power plug (12V socket). This can top up a slow leak, but it will not seal a puncture.
2) Sealant canister plus compressor. Often packaged together. The sealant is injected through the valve using the compressor, then you drive briefly to distribute it.
3) Sealant canister only. Less common. Without a compressor, you may not be able to reinflate enough to drive.
4) Run-flat tyres (no kit). Some vehicles rely on run-flats, but you still need to confirm whether driving is permitted and for how far.
If you collected your vehicle from a major hub such as Los Angeles (LAX) or San Jose (SJC), it is common to see mobility kits in place of spares, especially in newer models and EVs. What matters is not the airport, but the specific car and its equipment list.
When using sealant makes sense
Sealant is designed for one job: temporarily sealing a small puncture in the tread area so you can drive slowly to a tyre shop. It is not a proper repair, and it is not for every type of damage.
Sealant is most appropriate when all of the following are true:
The puncture is in the tread, not the sidewall or shoulder.
The hole is small, typically a nail or screw sized puncture.
The tyre is still holding some air, or can be reinflated and stays inflated long enough to move.
You can drive immediately after adding sealant. Sealant works by coating the inside and plugging the leak as the tyre rotates.
Even then, treat it as a short-distance solution. Keep speeds low and plan to get the tyre assessed as soon as possible.
When you should not use sealant, and should call for help
Sealant can fail, and it can create knock-on problems that affect the tyre, the wheel, and TPMS sensors. Do not use it in these situations, call the provider’s roadside assistance instead:
Sidewall or shoulder damage. Cuts, bulges, or punctures near the sidewall are unsafe and not reliably sealable.
A large hole or visible tear. If you can see a gash, or hear loud air loss, sealant is unlikely to work.
Tyre has come off the rim. If the bead is unseated, the tyre may not reseal properly with a basic compressor.
Wheel damage. If you hit a kerb or pothole and the wheel is bent or cracked, sealant will not help.
TPMS warning plus rapid pressure loss. A persistent warning after reinflation suggests a significant leak. Continuing to drive risks tyre destruction.
Unknown sealant instructions. Some kits have model-specific steps. If the instructions are missing or unclear, calling for guidance is safer than guessing.
In practice, if you are on the freeway shoulder anywhere in California, the “right” answer is often to call for help. The risk of being hit by traffic outweighs the convenience of a quick DIY fix.
How sealant can ruin a tyre, and what TPMS changes
Tyre sealant is messy by design. It coats the inside of the tyre, and it can affect components that sit inside the wheel.
TPMS sensors are commonly mounted at the valve stem or strapped to the wheel barrel. Sealant can clog the sensor port, interfere with pressure readings, or coat the sensor body. Some tyre shops will refuse to work on a tyre that has been filled with sealant, or they may charge extra for cleaning. If a sensor fails after sealant use, you may be asked to pay for replacement if it is considered avoidable damage.
Tyre repairability can change after sealant. A simple nail puncture that could have been patched might become more expensive if the inside is contaminated and needs extensive cleaning. It can also be harder to inspect the tyre properly.
Wheel and valve issues can arise if sealant blocks the valve core. You may have trouble adjusting pressure later.
None of this means sealant is always wrong. It means you should treat it as a last-mile tool and keep evidence that you used it appropriately for a small tread puncture, or that you avoided using it because it would likely cause damage.
A step-by-step decision check at the roadside
Use this quick process to decide whether to use the kit or call for assistance:
1) Check safety first. If you are not fully off-road, do not attempt a repair.
2) Look for the puncture location. If it is on the sidewall or shoulder, stop and call.
3) Check the tyre condition. If the tyre is shredded, flat on the rim, or the wheel is damaged, call.
4) Check the dashboard. Note any TPMS warnings, stability control lights, or messages. Photograph them.
5) Identify the kit. Confirm whether you have compressor only or compressor plus sealant. Photograph the kit.
6) Decide. If it is a small tread puncture and you can safely work, sealant can be reasonable. Otherwise call.
This is particularly relevant if you are driving longer distances in a larger vehicle, for example a people carrier from a California minivan rental at LAX. These tyres can be more expensive, and driving on them while underinflated can destroy the sidewalls quickly, turning a small problem into a full replacement.
If you do use the inflator and sealant, do it in a way that protects you
If you choose to proceed, follow the kit’s printed instructions exactly, as layouts differ. The general approach is:
1) Photograph first. Take clear photos of the puncture area if visible, the tyre’s overall condition, and the wheel.
2) Record the tyre info. Photograph the tyre size and brand on the sidewall, and the DOT code if you can see it.
3) Photograph the kit. Include the sealant canister label, brand, and any “single use” note.
4) Plug into the 12V socket. Keep the engine running if the manual permits, so you do not drain the battery.
5) Inflate to the specified pressure. Use the door jamb sticker for the target PSI, not the maximum PSI on the tyre sidewall.
6) Drive the recommended distance. Many kits require a short drive to distribute sealant, then a recheck.
7) Recheck pressure. If it will not hold pressure, stop and call for help. Continuing can destroy the tyre.
When you arrive at a tyre shop, tell them sealant was used. Do not let the sealant surprise the technician, it can be a safety issue when dismounting the tyre.
What to photograph and report to avoid charges
Charges disputes often come down to documentation. Your goal is to show (1) what happened, (2) that you did not drive recklessly on a flat tyre, and (3) that you followed sensible steps.
Photograph these items:
Dashboard warnings including TPMS message and time if visible.
Tyre from multiple angles, including the suspected puncture area and the sidewall.
Wheel and rim, especially if you suspect kerb or pothole impact.
Road context. A wide shot showing where you stopped can support that you prioritised safety.
The kit contents, including sealant canister and compressor model.
Pressure gauge reading if the compressor has one, before and after.
Then report promptly. Provide:
Location (nearest exit, cross street, or GPS).
What you observed (slow leak vs sudden blowout, tread nail vs sidewall cut).
What actions you took (inflated only, used sealant, or avoided sealant because of sidewall damage).
Whether you drove on it, and approximately how far.
This level of detail helps if the tyre ends up needing replacement, or if the TPMS sensor later triggers a fault after sealant use.
Common California scenarios and the best response
Urban kerb strike in Santa Ana. If you clipped a kerb and the tyre is losing air, check the wheel lip for bends and the sidewall for a bubble. If you see sidewall damage, do not use sealant. If you are arranging support or swapping vehicles, note your pickup point such as car hire at Santa Ana airport (SNA) for easier coordination.
Pothole hit near Sacramento. Potholes can pinch the tyre and crack the wheel. Sealant will not fix a bent rim. Photograph the wheel and call. If your trip started with Sacramento (SMF) car hire, include that in your report so records match the vehicle.
Slow nail leak on a long drive. If pressure drops gradually and the puncture is in the tread, a compressor-only top-up may be enough to reach a tyre shop without adding sealant. That can reduce the chance of TPMS contamination.
What to do after you are back on the road
After a temporary fix, treat the tyre as compromised. Avoid high speeds, hard cornering, and long distances. If the car still shows a TPMS warning, do not ignore it. Recheck pressure with the compressor, and if it drops again, stop driving and request assistance.
If sealant was used, expect that the tyre shop may recommend replacement rather than repair. Keep receipts and written notes from the shop, and share them with the rental provider if requested.
FAQ
Should I use the sealant in my California car hire tyre kit? Use it only for a small tread puncture when you can work safely off-road. If there is sidewall damage, a large hole, wheel damage, or the tyre will not hold pressure, call for help instead.
Can tyre sealant damage TPMS sensors? Yes. Sealant can clog or contaminate TPMS sensors and valves, causing faulty readings or sensor failure. If you suspect TPMS involvement, compressor-only inflation or roadside support can be safer.
Will I be charged if I use the sealant canister? It depends on the rental terms and what damage occurred, but you can reduce disputes by photographing the puncture, dashboard warnings, and kit contents, then reporting promptly with clear notes of what happened.
What if I only have a compressor and no sealant? Inflate to the door-sticker PSI and monitor whether pressure holds. If it drops again or you cannot reach safe assistance without losing pressure, stop and call roadside support.
Is it safe to keep driving after using sealant? Only as a temporary measure to reach professional help. Drive gently, recheck pressure shortly after, and stop if the tyre loses air again or handling changes.
