TPMS generates more comebacks than almost any other tire-related job, and nearly all of them are avoidable. The faults are predictable once you understand what the system is doing.
Two systems, very different behaviour
- Direct TPMS — a battery-powered sensor inside each wheel measuring actual pressure and transmitting it. Gives you real per-wheel numbers.
- Indirect TPMS — no sensors at all. It infers a low tire from wheel speed data, because an underinflated tire has a smaller rolling radius and turns faster.
This distinction explains a lot of customer confusion. Indirect systems can’t tell you which tire or by how much, and they must be reset after any pressure adjustment or rotation — otherwise they’re calibrated against the wrong baseline.
Sensor batteries die, and they aren’t serviceable
Direct sensors are sealed units with a finite battery life, typically running several years before they go. They fail gradually and often intermittently — a light that appears on cold mornings and clears later is a classic dying-sensor signature.
If a vehicle is old enough that one sensor has died, the others are the same age. Worth flagging so the customer isn’t back three more times over the following year.
Always fit the service kit
This is where most TPMS comebacks originate. Every tire change on a direct system should include a new valve core, grommet/seal, nut and cap.
The cores are nickel-plated for a reason — a standard brass core against an aluminium sensor stem causes galvanic corrosion, which seizes the assembly and creates a slow leak that looks like a bad bead seal. Diagnosing that twice is more expensive than the kit every time.
Handle the sensors properly during the job
- Break the bead away from the sensor, never over it.
- Torque the sensor nut to specification — these are easy to snap and easy to leave loose.
- Position the valve correctly relative to the mounting head before you start.
- Check the sensor is transmitting before the wheel goes back on the car.
Relearn procedures vary enormously
There are broadly three approaches, and which one applies is manufacturer-specific:
- Auto-relearn — the vehicle learns positions itself after a period of driving.
- Stationary relearn — a defined sequence, often using a tool to wake each sensor in order.
- OBD relearn — sensor IDs written to the module through the diagnostic port.
Look it up before the wheels come off, not after the light stays on. Guessing the sequence wastes more time than reading it.
Programmable and cloned sensors
Aftermarket programmable sensors either take a new ID for a relearn, or clone the original sensor’s ID so no relearn is needed. Cloning is quicker but only works if the original sensor still transmits — so if you plan to clone, read the IDs before you remove anything.
Faults that aren’t the sensor
Before condemning a sensor, rule out the cheap things:
- Genuinely low pressure — check it cold, because a warm tire reads higher.
- A spare with a sensor that the system is still monitoring.
- A recent rotation on an indirect system with no reset performed.
- Corroded valve hardware causing a slow leak, not a sensor fault at all.
- Aftermarket accessories or a nearby transmitter interfering with reception.
Explaining it at the counter
Customers think the light means a flat. Explain that the system typically triggers around 25% below the placard pressure, which is well before a tire looks low — and that a cold snap alone can drop pressure enough to trigger it. That single sentence prevents a great many irritated phone calls in November.
Learning this properly
TPMS is one of those areas where a bit of genuine knowledge separates you quickly, because so many shops treat it as guesswork. We cross-train technicians into diagnostic work rather than leaving them on the same jobs indefinitely — across our Midas shops in Wayne, Oakland and Washtenaw counties.