Wheels & Tires: Overview Ford Flex I

Principles of Operation

Note. The Smart Junction Box (SJB) is also referred to as the Generic Electronic Module (GEM).

The Tire Pressure Monitoring System (TPMS) monitors the air pressure of all 4 road tires. The wheel-mounted tire pressure sensors transmit via radio frequency signals, to the SJB . TPMS functionality is integral to the SJB . These transmissions are sent approximately every 60 seconds when the vehicle speed exceeds 32 km/h (20 mph). The TPMS function compares each tire pressure sensor transmission against a low-pressure limit. If it has been determined that the tire pressure has fallen below this limit, the SJB communicates this on the vehicle communication bus to the instrument cluster. The instrument cluster then illuminates the TPMS indicator and displays the appropriate message(s) in the message center (if equipped).

For vehicles with different front and rear tire pressures (such as the E-Series and certain F-Series), the tire pressures must be adjusted and the tire pressure sensors must be trained following a tire rotation. Failure to train the sensors will cause the TPMS indicator to illuminate.

For vehicles with the same tire pressures for front and rear tires, tire rotation will not affect the system.

Normal Operation

The Tire Pressure Monitoring System (TPMS) monitors the air pressure of all 4 road tires. The wheel-mounted tire pressure sensors transmit via radio frequency signals, to the Smart Junction Box (SJB). TPMS functionality is integral to the SJB . These transmissions are sent approximately every 60 seconds when the vehicle speed exceeds 32 km/h (20 mph). The TPMS function (integral to the SJB ) compares each tire pressure sensor transmission against a low-pressure limit. If it has been determined that the tire pressure has fallen below this limit, the SJB communicates this on the vehicle communication bus to the Instrument Cluster (IC). The IC then illuminates the TPMS indicator and displays the appropriate message(s) in the message center (if equipped).

This symptom can also be caused by a spare tire currently being used in place of a road tire. Make sure that the spare tire is not currently in use. On vehicles with different front and rear tire pressures, if the sensors are not trained following a tire rotation, this symptom will also be present. Advise the customer that on vehicles with different front and rear tire pressures, the sensors must be trained as directed in the Owner's Literature.

This pinpoint test is intended to diagnose the following

1. Low air pressure in tire(s)
2. Tire pressure sensor(s)

For the Smart Junction Box (SJB) to enter Tire Pressure Monitoring System (TPMS) sensor training mode, the SJB must receive valid inputs from the Brake Pedal Position (BPP) switch (OFF-ON-OFF) and ignition switch (both OFF and RUN), and it must receive valid vehicle speed sensor input (0 km/h [0 mph]). Refer to TIRE PRESSURE MONITORING SYSTEM (TPMS) SENSOR TRAINING for the complete sensor training procedure.

This pinpoint test is intended to diagnose the following

1. Wiring, terminals or connectors
2. Brake ON/OFF switch
3. Ignition switch
4. SJB

If there is a fault with 1, 2 or 3 of the Tire Pressure Monitoring System (TPMS) sensors, DTC B2872 will be set, the TPMS warning indicator will flash for 70 seconds and then remain ON solid when the ignition switch is turned to the ON position and the message center (if equipped) will display TIRE PRESSURE SENSOR FAULT.

If the Smart Junction Box (SJB) does not get a response from all 4 of the TPMS sensors, DTC B287A will be set and the message center (if equipped) will display TIRE PRESSURE MONITOR FAULT.

1. DTC B2872 (Tire Pressure Sensor Fault) - When 1, 2 or 3 of the tire pressure sensors are faulted or not responding, the SJB will set DTC B2872.
2. DTC B287A (Tire Pressure Monitor Fault) - When all 4 of the tire pressure sensors are faulted, not responding or not heard by the SJB , the SJB will set DTC B287A.

This pinpoint test is intended to diagnose the following

1. TPMS sensor(s) missing
2. TPMS sensor(s) not trained to the vehicle
3. TPMS sensor(s) swapped due to wheel swap
4. TPMS sensor(s) damaged
5. Vehicle communication issue
6. SJB

This DTC may be encountered if a sensor designed for a different application is installed. Low pressure applications utilize a black- or blue-colored sensor, while heavy duty applications utilize a green-colored sensor. The Smart Junction Box (SJB) will only allow one type of sensor to be trained using the Tire Pressure Monitoring System (TPMS) sensor training procedure. Make sure the correct sensors are used to avoid compatibility issues.

1. DTC B106A (Pressure Sensor Range Bit Incorrect State) - When an attempt has been made to train a non-compatible sensor, the SJB will set DTC B106A.
2. Incorrect tire pressure sensor(s) installed

If there is a fault in the Tire Pressure Monitoring System (TPMS), such as a damaged or missing sensor(s), damaged module or a communication issue within the vehicle, DTCs are set in the Smart Junction Box (SJB), the TPMS warning indicator will flash for 70 seconds and then remain ON solid when the ignition switch is turned to the ON position and the message center (if equipped) will display TIRE PRESSURE SENSOR FAULT.

The tire pressure sensor is battery powered.

This DTC may be set when attempting to train a tire pressure sensor(s) with a low battery.

This pinpoint test is intended to diagnose the following

1. Tire pressure sensor battery
2. Tire pressure sensor(s)