A TPMS light is easy to ignore until the message changes from a warning to something blunter, like the dash telling you the sensors cannot be connected. That is what came in on this 2016 Mk7 Fiesta, and it is a fault a lot of people take straight to a garage for a diagnostic charge.
Here is the part that catches people out, including some garages: a dead TPMS sensor does not reliably show up on a diagnostic scanner. A scanner talks to the car, and the car is telling it that a sensor has stopped reporting, not which one has failed or why. If you want to know which of the four wheels holds the dead sensor, you have to go and ask each sensor directly.
That takes one cheap tool and about twenty minutes. This guide covers finding the faulty sensor and then completing the relearn once the new one is fitted, which is the same procedure either way.
The tool you actually need
A TPMS activation or relearn tool is a small handheld unit that wakes a sensor up and confirms it is transmitting. They cost a few pounds and are the only way to test sensors individually. Do not confuse it with an OBD scanner, which plugs into the car and cannot tell you which wheel is the problem.
What You Need
Ford Fiesta Owner's Bible (Mk7 & Mk8)
- Mk7 and Mk8 specific faults, service intervals and torque figures
- The known weak points and what they cost to put right
- Written around the Fiesta, not a generic car guide
Instant PDF download · works on phone, tablet or PC · 7-day money-back guarantee
Step-by-Step: Find the Dead Sensor
Park up and switch the ignition off
Start from a completely off state, with the car stationary and the doors shut. The relearn sequence relies on the car seeing a clean set of inputs, so if you have been cycling the ignition while poking at the fault, turn everything off and let it settle for a few seconds before you begin.
Enter TPMS relearn mode
With the ignition off, press the brake pedal on and off once. Then cycle the ignition on and off three times, leaving it in the on position on the third. Press the brake pedal on and off again, then cycle the ignition on, off, on, off, on. The horn will sound a short beep, which is the car confirming it is now in relearn mode. If you get no beep, you have missed a step in the sequence, so switch off and start again rather than pressing on.
Read which wheel the dash is asking for
Once you are in relearn mode the display tells you which wheel it wants, starting with the left front. The car works through the wheels in a set order and will not move on until it has heard from the one it is asking about, so follow the dash rather than working round the car in whatever order suits you.
Hold the tool against the first sensor and wait for the beep
Hold the activation tool against the tyre sidewall next to the valve, at the wheel the dash has asked for, and press it. A working sensor answers and the car beeps to confirm it has heard. The display then moves on to the next wheel.
Work round the car and note which wheel stays silent
Repeat at each wheel in the order the dash asks for. On the Fiesta in the video, three wheels answered and the driver side rear stayed silent no matter how many times it was activated. That silence is your diagnosis: the sensor in that wheel is dead and no amount of relearning will bring it back. Try the silent one twice from slightly different positions before condemning it, just to rule out simply having missed the sensor.
Fit a new sensor to the wheel that failed
The sensor lives on the valve inside the tyre, so this part means breaking the bead. If you are not set up for tyre work, this is the point to hand the wheel to a tyre shop with the new sensor, which is a small job for them. Make sure the replacement is the correct type and frequency for your Fiesta, because a sensor that physically fits is not necessarily one the car will talk to.
Run the whole relearn again from the start
With the new sensor fitted and the wheel back on, repeat the entire sequence from step two. Brake pedal, three ignition cycles, brake pedal, five ignition cycles, wait for the beep. Then activate all four wheels in the order the dash asks for, including the ones that were fine, because the car is rebuilding the whole set rather than patching in one sensor.
Confirm training complete, then road test
When all four have answered, the display reads training complete. Turn the ignition off, start the car normally and check the TPMS warning has cleared. Take it for a short drive so the system settles with the wheels turning. If the light stays off after a proper run, the job is done and you will get a genuine warning next time a tyre actually goes down.
Why the Scanner Did Not Tell You Which Wheel
This is worth understanding, because it is why the job gets misdiagnosed. Your car's TPMS module knows that it is no longer hearing from one of the four sensors it expects. What it does not have is a way to tell you which physical corner that missing sensor sits in, because the identity of a sensor is something the car learns during a relearn rather than something it can look up on demand.
So a scanner reads the fault as a system-level complaint. Sensors not connecting, TPMS fault, and so on. Plugging in and reading codes tells you what you already knew from the dashboard. The activation tool works the other way round, going directly to each sensor and asking it to transmit, which is why it can point at one wheel when the scanner cannot.
That difference is also why a garage that only owns a scanner may quote you for replacing all four sensors. If the sensors are genuinely old and batteries are failing across the set, that can be reasonable. If only one has died, it is three sensors more than you needed.
How Long TPMS Sensors Last
The sensor is a small battery-powered radio sealed inside a unit that lives in a wheel, so the battery is not replaceable. Typical life is somewhere around seven to ten years, and once one goes it is fair to assume the others are the same age and heading the same way.
That does not mean replacing all four the moment one fails, but it does mean planning. If yours is a ten year old car on its original sensors, expect the others in the next couple of years, and it is worth doing them as tyres are changed rather than as separate jobs, since the wheel is already off the car and the tyre already off the rim.
The other common killer is corrosion at the valve, particularly on aluminium valve stems that have been sat in road salt. If your sensor has died young, look at the valve condition before assuming a battery failure.
Is a TPMS Fault an MOT Failure?
Yes, on cars that were required to have the system. For vehicles first used from 1 January 2012, a TPMS malfunction indicator showing a fault is a major defect and the car fails the test. That makes this a job with a deadline rather than a warning light you can live with.
The other thing worth saying is that the system is genuinely useful. A slow puncture that would otherwise go unnoticed until the tyre is ruined or the car handles badly gets flagged early. Once your TPMS is dead you lose that, so the whole system is off duty until the faulty sensor is replaced.
Common Mistakes
- Assuming a scanner will name the wheel. It will not. It reports a system fault, and that is all it can do.
- Rushing the ignition sequence. Miss a cycle and you never enter relearn mode. If there is no horn beep, stop and start over.
- Working round the car in your own order. Follow the wheel the dash asks for, or the relearn will not complete.
- Condemning a sensor after one attempt. Activate the silent wheel a second time from a slightly different spot before buying anything.
- Fitting a sensor that is not the right type for the car. Physically fitting is not the same as being compatible.
- Skipping the relearn after fitting. A new sensor the car has never been introduced to is just a sensor the car cannot hear.
- Ignoring the light because the tyres look fine. It is a major MOT defect on any car first used from 2012.
