Ford S-Max low tire pressure warning light causes, how to reset

Ford S-Max is equipped with Tire Pressure Monitoring System (TPMS) for the purpose of warning the driver when one or more of the tires are significantly under-inflated, creating a potentially unsafe driving condition. In this article we discuss the reasons for the amber colored TPMS warning light in S-Max, and how you can reset it.

Ford S-Max
Ford S-Max – (yakub88 / Shutterstock)

The TPMS warning light illuminates in Ford S-Max when air pressure is low in one or more of the tires, battery has depleted in a pressure sensor, TPMS receiver module has malfunctioned, or a pressure sensor has been damaged.


Low tire pressure

When the amber colored TPMS warning light turns on in your S-Max, stop your vehicle when it is safe to do so and check tire pressure on all the wheels, including the spare wheel (if your vehicle has one). Driving on a significantly under-inflated tire causes the tire to overheat and can lead to tire failure.

Reinflate the tires

Reinflate all the tires of your S-Max to the manufacturer specified air pressure, which is mentioned on the vehicle placard or tire inflation pressure label usually located on the B-pillar or the edge of the driver door. If you can’t find the label, check the size of your tire which is mentioned on the sidewall of the tire, and match it to the tire pressure information shown below. These are official cold tire pressure values for S-Max from Ford.

  • 235/55R17 103V: Front: 2.6 bar (38 psi), Rear: 2.4 bar (35 psi)
  • 235/55R17 103V All Season/Winter: Front: 2.4 bar (35 psi), Rear: 2.4 bar (35 psi)
  • 235/50R18 101V: Front: 2.4 bar (35 psi), Rear: 2.2 bar (32 psi)
  • 235/50R18 101W: Front: 2.4 bar (35 psi), Rear: 2.2 bar (32 psi)
  • 235/50R18 101Y: Front: 2.6 bar (38 psi), Rear: 2.4 bar (35 psi)
  • 245/45R19 102V: Front: 2.6 bar (38 psi), Rear: 2.4 bar (35 psi)
See the sidewall of any tire on your S-Max to find the tire size information.

Resetting the TPMS warning light

You must reset the tire pressure monitoring system after each tire replacement, tire rotation or after inflating the tires to the correct tire pressure in your S-Max.

If you have a new sensor or have rotated the vehicle tires, park your vehicle for at least 20 minutes, before resetting the system.

The tire pressure monitoring system automatically re-learns the tire pressure sensors the next time you drive your vehicle for approximately 15 minutes.

  1. Turn on the ignition or start the vehicle.
  2. Using the information display controls on the steering wheel, select Driver assist.
  3. Select Tire monitor.
  4. Select Reset.
  5. Press and hold the OK button until the system reset confirmation appears.

Video Demonstration

Watch this video to see how to reset TPMS system in Ford S-Max.

If the low tire pressure light does not turn off automatically after reinflating the tires in your S-Max, increase the tire pressure by 5 psi on top of the factory recommended value, and drive your vehicle for at least 10 miles (16 km). After the TPMS warning light turns off, and the vehicle has been parked for a few hours, reduce the tire pressure to the factory recommended value.


Chilly weather can turn on low tire pressure light in S-Max

Cold weather is one of the most common cause for low tire pressure warning light in Ford S-Max. When analyzing WheelsJoint’s statistical data, it has been observed that there is sharp rise in the number of searches for TPMS warning light causes at the start of every winter season, about three times higher as compared to mid summer season.

The air, like most other substances, expands when heated and contracts when cooled. So when the weather gets colder, the tire pressure decreases, which could trigger TPMS warning light in S-Max. The tire pressure will vary with temperature by about 1 psi (7 kPa) for every 12°F (6.5°C).

Tire pressure vs temperature: This chart shows how tire pressure of 35 psi at temperature of 35°C (95°F) decreases by roughly 1.6 psi with every 10°C (18°F) drop in temperature.

Inflate tires when cold

Tire pressure in S-Max should always be set based on cold inflation tire pressure. This is defined as the tire pressure after the vehicle has not been driven for at least three hours, or driven less than 1 mile (1.6 km) after a three-hour period.

Do not adjust tire pressure when hot

The tires on your S-Max can get around 50 degrees hotter than the outside temperature when you’re driving, which increases the tire pressure by about 4 psi – this is normal and there should be no adjustment for this increased pressure.

Does altitude affect tire pressure?

Yes, altitude can change tire pressure values, but it is negligible and not a cause for concern. If you drive your S-Max from sea level to Mount Evans Scenic Byway in Colorado which is the highest paved road in North America at the altitude of 14,130 feet (4,307 m), the tire pressure should theoretically increase by approximately 6 psi. But, the decrease in ambient temperature at higher elevation contracts the air in tires and compensates for any altitude pressure changes.

Is it safe to drive S-Max with low tire pressure?

The driving characteristics of S-Max change even if the air pressure is 5 psi less than manufacturer’s recommended value: the braking distance can be longer, cornering worse, and at particularly high speeds there is even a risk that the tire will burst. Low tire pressure also increases tire wear, and the higher rolling resistance of the tire means higher fuel consumption. So it is recommended to reinflate the tires to the correct pressure as soon as possible.

Dead battery in a tire pressure sensor

Each tire pressure sensor in S-Max is powered by a built-in lithium-ion battery. When the battery is depleted, the sensor stops transmitting tire pressure information to the receiver module. When this happens, the TPMS warning light will flash every time the engine is started, and will remain illuminated until you turn off the vehicle.

How long do the pressure sensor batteries last?

The tire pressure sensor batteries usually last anywhere from 5 to 10 years in S-Max. When the battery is depleted, you must replace the sensor itself, as the battery is sealed into the sensor unit and is non-replaceable.


Identifying a faulty pressure sensor

The most reliable method for detecting a faulty tire pressure sensor or a sensor with dead battery is by testing each sensor with a scan tool. For example, MaxiTPMS TS408 is commonly used for diagnosing and programming tire pressure sensors. A sensor that is not detectable by the scanner is most likely defective and should be replaced with a new one.

Scan each wheel with a scan tool like MaxiTPMS TS408 and see which one does not respond.

If you don’t want to spend over a hundred bucks on a scanner, then head over to any reputable tire shop and perform a TPMS diagnostic scan of your S-Max.

Installed new tires?

If a pressure sensor stopped responding after you installed new tires on your S-Max, it is possible the sensor got damaged during tire installation. These sensors are quite sensitive, and can be easily damaged if utmost care is not taken while changing tires.

Ford S-Max TPMS user guide

The tire pressure monitoring system measures the vehicle’s tire pressures. A warning lamp illuminates if one or more tires are significantly underinflated or if there is a system malfunction.

WARNING: The tire pressure monitoring system is not a substitute for manually checking tire pressures. You should periodically check tire pressures using a pressure gauge. Failure to correctly maintain tire pressures could increase the risk of tire failure, loss of control, vehicle rollover and personal injury.

WARNING: Do not use the tire pressure displayed in the information display as a tire pressure gauge. Failure to follow this instruction could result in personal injury or death.

Note: The use of tire sealants can damage the tire pressure monitoring system.

TPMS Limitations

The warning lamp can illuminate when:

  • You use a spare wheel or a tire sealant and inflator kit.
  • The outside air temperature drops significantly. The tire pressure could decrease and activate the low tire pressure warning lamp. Check each tire to verify that none are flat. Inflate the tires, if needed, to the recommended pressures and carry out the reset procedure.

Note: Regularly checking the vehicle tire pressures can reduce the possibility for the warning lamp to illuminate due to outside air temperature changes.

Note: After you inflate the tires to the correct pressure, it may take up to two minutes of driving over 32 km/h (20 mph) for the warning lamp to turn off.

Troubleshooting TPMS warning light

Solid warning lamp: One or more tires are significantly underinflated. Inflate the tires to the recommended tire pressure. Check the tires for damage and repair them if necessary. Carry out the system reset procedure.

Solid warning lamp or flashing warning lamp: Temporary spare wheel in use. Repair the damaged road wheel and tire and refit it to your vehicle to restore the correct operation of the system.

Solid warning lamp or flashing warning lamp: Tire pressure monitoring system malfunction. If the tires are inflated to the recommended tire pressures and the temporary spare wheel is not in use, the system has detected a fault that requires service. Have your vehicle checked as soon as possible.

Tire Pressure Monitoring System – Information Messages

Tire pressure low: Inflate the tires to the recommended tire pressure. Check the tires for damage and repair them if necessary. Carry out the system reset procedure.

Tire pressure monitor malfunction: The system has detected a fault that requires service. Have your vehicle checked as soon as possible.

Tire pressure sensor malfunction: The temporary spare wheel is either in use or the system has detected a fault in the sensor that requires service. Have your vehicle checked as soon as possible.

Reset the entire system

If the low tire pressure warning light won’t turn off due to a glitch in the tire pressure monitoring system, it may be possible to reset the TPMS system by resetting all on-board computers in your S-Max. This method should only be considered as a last resort, when all else fails.

Disconnect both negative and positive terminals of the battery.

You can reboot all the on-board computers by disconnecting the main 12 volt battery for a few minutes. Remove the cable from the negative terminal of the battery first, then from the positive terminal. With the battery disconnected, press the horn button a few times and turn on the headlights to drain out all the residual electricity from the system. After about 15 minutes, reconnect the battery in reverse order: positive cable first, then negative cable.

Tire pressure keeps getting low

If the TPMS warning light turns on frequently in your S-Max, and the tire pressure is also decreasing after you have reinflated the tires, there may be an air leak. One or more of the tires may have been punctured by an external object, or the air may be leaking from a defective value stem.

A punctured tire can be plugged with a tire repair kit if the puncture is not near the sidewall.

Use OBD2 scanner for diagnosis

Since Ford S-Max is equipped with on-board diagnostics (OBD), a fault diagnosis can provide initial indications of where the malfunction is located. But when it comes to TPMS, a basic code reader will not suffice. You will need an advanced scanner to monitor TPMS data or read TPMS codes.

BlueDriver is a Bluetooth based diagnostic device which you can connect to the OBDII port in your vehicle and use your mobile phone for diagnosis. You will need to download the “BlueDriver OBD2 Scan Tool” app from the App Store on your iPhone, or from Google Play Store if you have an Android phone.

BlueDriver is a commonly used scanner by DIYers that can read TPMS codes for most vehicles and isn’t too expensive – costs about a hundred bucks. You can also clear the TPMS fault codes with this device which will turn off the warning light, but the light may come back on if the on-board diagnostic system detects a fault again.

Author: Nabeel K
Email: nabeel@wheelsjoint.com