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Home >> Ford Truck >> 2012 >> Explorer FWD L4-2.0L Turbo >> Repair and Diagnosis >> Steering and Suspension >> Wheels and Tires >> Tire Monitoring System >> Description and Operation >> System Operation

System Operation




Tire Pressure Monitoring System

System Operation

System Diagram





Network Message Chart

TPM (Tire Pressure Monitor) Module Network Input Messages






Tire Pressure Monitoring System (TPMS) Function

NOTE: When directed to train or re-train any TPMS (Tire Pressure Monitoring System) sensors, use only the sensor training procedure outlined in REFER to Tire Pressure Monitoring System (TPMS) Sensor Training - Intelligent Access (IA) Tire Pressure Monitoring System (TPMS) Sensor Training - Intelligent Access (IA) or REFER to Tire Pressure Monitoring System (TPMS) Sensor Training - Integrated Keyhead Transmitter (IKT) Tire Pressure Monitoring System (TPMS) Sensor Training - Integrated Keyhead Transmitter (IKT). Do not use the TPMS (Tire Pressure Monitoring System) reset procedure outlined in the Owner's Literature as this procedure will not program new sensors to the module.

The TPMS (Tire Pressure Monitoring System) system monitors the tire pressure using 4 valve stem mounted TPMS (Tire Pressure Monitoring System) sensors to provide accurate tire pressures. Each individual sensor contains its own battery and transmits tire pressure data to the TPM (Tire Pressure Monitor) module. The TPM (Tire Pressure Monitor) module is a radio receiver that collects the tire pressure data and relays the information via the MS-CAN (Medium Speed Controller Area Network) to the BCM (Body Control Module). All of the TPMS (Tire Pressure Monitoring System) functions are controlled by the BCM (Body Control Module). The TPMS (Tire Pressure Monitoring System) sensors are trained to the BCM (Body Control Module), which records the unique identifier for each TPMS (Tire Pressure Monitoring System) sensor. The BCM (Body Control Module) records where each TPMS (Tire Pressure Monitoring System) sensor is located based on the training order and compares the actual tire pressure with the desired tire pressure as indicated on the VC (Vehicle Certification) label. If the tire pressure deviates from the desired tire pressure the BCM (Body Control Module), using the HS-CAN (High Speed Controller Area Network), signals the IPC (Instrument Panel Cluster) to illuminate the TPMS (Tire Pressure Monitoring System) warning indicator and also displays a message on the message center. The programmed tire pressure cannot be changed.

The scan tool is a useful tool in diagnosing TPMS (Tire Pressure Monitoring System) concerns and may be used to verify if the TPMS (Tire Pressure Monitoring System) sensors are transmitting accurate tire pressure data by comparing the PID (Parameter Identification) tire pressure data in the BCM (Body Control Module) to the actual tire pressure using a digital tire pressure gauge. Training the sensors is not necessary after a tire rotation on vehicles with the same front and rear tire pressures, but the BCM (Body Control Module) cannot recognize that the sensor identifiers have been moved to different positions, it only retains the original position the sensors were last trained to.

Wheel Rotation and Sensor Training Techniques

Training known good sensors from another vehicle cannot differentiate between a faulted module and RFI (Radio Frequency Interference), as some noise source could be preventing the TPM (Tire Pressure Monitor) module from receiving the tire pressure status from the original sensors as well as the known good sensors. This technique can be used to differentiate between a sensor and module issue. If the TPM (Tire Pressure Monitor) module in the vehicle cannot train any of the sensors on the same vehicle, and likewise cannot train known good sensors from another vehicle, then the issue is with the module or RFI (Radio Frequency Interference) and not with the original sensors. The original sensors should not be replaced. If a sensor in a certain location has caused several events, yet the sensor trains and seems to operate normally, moving that particular wheel to a different location on the vehicle is a good way to isolate the issue to a certain sensor/wheel location. Rotate the wheels and road test the vehicle. This can be done in an attempt to replicate the issue and help determine if the issue followed the sensor or remained in the original sensor location. If the vehicle has been stationary for more than 30 minutes, the sensors go into a "sleep mode" to conserve battery power. It becomes necessary to wake them up so they transmit the latest tire pressure information to the TPM (Tire Pressure Monitor) module. REFER to Tire Pressure Monitoring System (TPMS) Sensor Activation Tire Pressure Monitoring System (TPMS) Sensor Activation.

Training Sensors in a Different Order

If the first sensor fails the TPMS (Tire Pressure Monitoring System) training procedure, the BCM (Body Control Module) aborts the entire procedure. Starting the training procedure at a different wheel is a technique that can be used to determine if the remaining sensors can train to the module. This can help save time determining if one sensor is damaged, other sensors are having issues, or the BCM (Body Control Module) is experiencing training difficulties with a certain TPMS (Tire Pressure Monitoring System) sensor location.

Tire Pressure Monitoring System (TPMS) Indicator

The TPMS (Tire Pressure Monitoring System) indicator and vehicle message center sometimes display faults that cannot be resolved by the customer. Treat these messages as TPMS (Tire Pressure Monitoring System) faults that must be serviced.

TPMS (Tire Pressure Monitoring System) Warning Indicator Illuminates Continuously

The TPMS (Tire Pressure Monitoring System) warning indicator remains on continuously and the message center displays LOW TIRE PRESSURE when any of the tire pressures fall below the low pressure limit. When this condition exists, adjust the tire pressure to the recommended cold tire pressure indicated on the VC (Vehicle Certification) label.

TPMS (Tire Pressure Monitoring System) Warning Indicator Flashes

The TPMS (Tire Pressure Monitoring System) warning indicator flashes for 70 seconds, then remains on continuously when the ignition is turned to the ON position when the TPMS (Tire Pressure Monitoring System) is malfunctioning. The PID (Parameter Identification) TP_STAT can be used to determine why the TPMS (Tire Pressure Monitoring System) warning indicator is flashing.

- Tire Pressure Sensor Fault - The message center displays TIRE PRESSURE SENSOR FAULT when a TPMS (Tire Pressure Monitoring System) sensor is malfunctioning. REFER to DTC AND SYMPTOM CHART(S) DTC Chart: Tire Pressure Monitor (TPM) Module Symptom Related Diagnostic Procedures.
- No communication with the BCM (Body Control Module) - The TPMS (Tire Pressure Monitoring System) warning indicator illuminates when the IPC (Instrument Panel Cluster) has not received any signals from the BCM (Body Control Module) for more than 5 seconds. The message center displays TIRE PRESSURE MONITOR FAULT. REFER to DTC AND SYMPTOM CHART(S) DTC Chart: Tire Pressure Monitor (TPM) Module Symptom Related Diagnostic Procedures.
- Tire Pressure Monitor Fault - The message center displays TIRE PRESSURE MONITOR FAULT when the TPMS (Tire Pressure Monitoring System) is malfunctioning. REFER to DTC AND SYMPTOM CHART(S) DTC Chart: Tire Pressure Monitor (TPM) Module Symptom Related Diagnostic Procedures.

Tire Pressure Monitoring System (TPMS) PID Definitions

The BCM (Body Control Module) monitors the TPMS (Tire Pressure Monitoring System) status. The current status can be viewed by accessing the TPMS (Tire Pressure Monitoring System) status PID (Parameter Identification): TPMS_STAT using the scan tool. This helps identify the current system status and may aid in diagnosing the system. The PID (Parameter Identification) has 4 valid states:

- TPMS_STAT = SENSOR FAULT If the BCM (Body Control Module) has not received the tire pressure data from 1 to 3 TPMS (Tire Pressure Monitoring System) sensors for 20 minutes when the vehicle speed is above 32.2 km/h (20 mph), the PID (Parameter Identification) displays SENSOR FAULT.

- TPMS_STAT = SYSTEM FAULT If the BCM (Body Control Module) has not received the tire pressure data from all 4 sensors for 20 minutes when the vehicle speed is above 32.2 km/h (20 mph), the PID (Parameter Identification) displays SYSTEM FAULT.

- TPMS_STAT = LOW If the BCM (Body Control Module) has detected that at least 1 TPMS (Tire Pressure Monitoring System) sensor is reporting low tire pressure, the PID (Parameter Identification) displays LOW.

- TPMS_STAT = ACTIVE If the TPMS (Tire Pressure Monitoring System) is functioning normally, the PID (Parameter Identification) displays ACTIVE.

Last Warning Event PID (Parameter Identification) Definitions

The TPMS (Tire Pressure Monitoring System) uses the TPMS (Tire Pressure Monitoring System) last warning event PIDs (Parameter Identifications) to store detailed information about the last 5 times the TPMS (Tire Pressure Monitoring System) warning indicator was activated. These PIDs (Parameter Identifications) can be used to acquire more information about a particular TPMS (Tire Pressure Monitoring System) event, but must be used carefully.







Radio Frequency Interference

The following equipment has been found to cause RFI (Radio Frequency Interference):
- Video equipment has been found to cause RFI (Radio Frequency Interference) especially when the video and power supply lines are near the TPMS (Tire Pressure Monitoring System).
- Car alarms (even those installed by the dealership) have been found to create enough RFI (Radio Frequency Interference) to cause the TPMS (Tire Pressure Monitoring System) to malfunction or lose considerable range. These car alarms can be difficult to locate, as they are usually hidden somewhere out of the way for reduced accessibility.
- Many in-vehicle cell phone chargers have been found to cause considerable RFI (Radio Frequency Interference). The vehicles with the power point closest to the TPM (Tire Pressure Monitor) module are the most affected. It must be noted that most cell phone chargers do not produce high levels of RFI (Radio Frequency Interference) all the time. This depends on the state of charge of the cell phone battery. The phone battery must be almost completely discharged in some cases.
- Power supplies and DC (Direct Current)/ AC (Alternating Current) inverters typically create a lot of RFI (Radio Frequency Interference). Most consumer grade equipment has very little filtering or shielding.

OEM (Original Equipment Manufacturer) Modules

In some cases the RFI (Radio Frequency Interference) may actually be caused by a module or ground on the vehicle. Depending on the severity of the issue, a dirty ground, improperly built ground shield or module can disable the system. Modules that have microcontrollers using clock circuits to create timing pulses for the microprocessor may radiate RFI (Radio Frequency Interference).

Using Customer's Electronics to Pinpoint Radio Frequency Interference

This method can be a way to determine the cause of an issue well before the sensors and module are replaced with little or no effect on the system performance. Since this takes more up front work, it relies on working with the customer to determine what equipment was being used at the time of the event. Question the customer about what kind of devices they are using. Determine which power points are being used and if necessary ask that the devices be activated to determine their affect on the TPMS (Tire Pressure Monitoring System).

Options for Eliminating Intermittent TPMS (Tire Pressure Monitoring System) Operation Caused by RFI (Radio Frequency Interference)

- If an OEM (Original Equipment Manufacturer) component or customer device is causing an RFI (Radio Frequency Interference) issue, replace the device.
- If a phone charger is causing an RFI (Radio Frequency Interference) issue, the customer should consult with their cell phone provider to acquire a different battery charger.
- If a device such as a dealer installed alarm is causing an RFI (Radio Frequency Interference) issue, move the device to another location in the vehicle. In the case of a portable device move the power cord to another power point location.
In summary, if the RFI (Radio Frequency Interference) source is present and cannot be moved or replaced, the intermittent issue remains. The TPMS (Tire Pressure Monitoring System) must accept the unwanted system operation it can cause.

Ambient Temperature Change and Tire Pressure

Tire pressures fluctuate with temperature changes. For this reason, tire pressures must be set to specification when tires are at outdoor ambient temperatures. If the vehicle is allowed to warm up to shop temperatures, and the outside temperature is less than shop temperature, the tire inflation pressure must be adjusted accordingly.

If the tires are inflated to specification at shop temperatures, and the vehicle is moved outdoors when the outdoor ambient temperature is significantly lower, the tire pressure may drop enough to be detected by the TPMS (Tire Pressure Monitoring System) and activate the TPMS (Tire Pressure Monitoring System) warning indicator.

As the ambient temperature decreases by -12.2 C (10 F) tire pressure decreases 6.9 kPa (1 psi). Adjust the tire pressure by 6.9 kPa (1 psi) for each-12.2 C (10 F) ambient temperature drop as necessary to keep the tire at the specified VC (Vehicle Certification) label pressure. To adjust the tire pressure indoors for colder outside temperatures:




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