Originally Posted by jsr72
That's not what I was asking, it was the comment about not being able to detect when all four tires are low at the same pressure.
Direct systems measure the actual pressure for each tire, not pressure differentials between tires.
Since it did not seem to sound the alarm when all the tires were equally low it seems that its still only caring about the pressure differential unless its low enough per the O.P.'s case. All four tires were exactly at the same pressure initially which was way low, but they said there was no alert from the system which you would think it would be if it actually knew enough to report which tire/ sensor had which pressure. Currently the system does not appear to be capable of displaying this information.
Ergo if it cared about absolute pressure being low on one or more tires at the same time should have gone off with them all equally too low, but that's not what it did.
That could be indicative of a failure in programming or an RF interference however as it should have gone off, but others have also reported that either with new sensors that weren't programmed, or without sensors sometimes it still takes a long long time for it to error out.
Does seem to be a malfunctioning system per the service manual, but not like Ford would actually fix anything at all ever.
The TPMS system monitors tire pressure using 4 valve stem mounted TPMS sensors, these sensors transmit tire pressure data to the BCM. The TPMS sensor locations and unique identifiers are trained (calibrated) to the BCM based on the training order. The BCM compares the tire pressure data sent by the sensors with a programmed desired tire pressure. This programmed pressure is the same pressure indicated on the VC label. If the tire pressure deviates from the programmed tire pressure the BCM, using the Medium Speed Controller Area Network (MS-CAN), signals the IPC to illuminate the TPMS warning indicator and to also display a message on the message center. The programmed desired tire pressure cannot be changed.
The scan tool is a useful tool in diagnosing TPMS concerns and may be used to verify the accuracy of the tire pressure data transmitted by the TPMS sensors. This is accomplished by comparing the BCM tire pressure Parameter Identification (PID) data 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 however, the BCM cannot recognize that the sensor identifiers have been moved to different positions and will retain the original position information for each sensor.
Wheel Rotation and Sensor Training Techniques
Training known good sensors from another vehicle cannot differentiate between a faulted module and Radio Frequency Interference (RFI), as some noise source could be preventing the 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 a module concern. If the module in the suspect vehicle cannot train any of the sensors on the vehicle and, likewise, cannot train known good sensors from another vehicle, then the concern is with the module or Radio Frequency Interference (RFI) 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 concern to a certain sensor/wheel location. Rotate the wheels and road test the vehicle. This can be done in an attempt to replicate the concern and help determine if the concern 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 and they will need to be "woken up" so they transmit the latest tire pressure information to the BCM.
Refer to: Tire Pressure Monitoring System (TPMS) Sensor Activation (204-04B Tire Pressure Monitoring System (TPMS), General Procedures).
Training Sensors in a Different Order
If the first sensor fails the TPMS training procedure, the BCM 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 concerns or the BCM is experiencing training difficulties with a certain TPMS sensor location.
TPMS Warning Indicator
The TPMS warning indicator and vehicle message center occasionally displays faults that cannot be resolved by the customer. Treat these messages as TPMS faults that must be serviced.
TPMS Warning Indicator Illuminates Continuously
The TPMS 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 label.
Tire Pressure Monitoring System (TPMS) Warning Indicator Flashes
The TPMS warning indicator flashes for 70 seconds and then remains on continuously when the ignition is set to ON and the TPMS is malfunctioning. The Parameter Identification (PID) TP_STAT can be used to determine why the TPMS warning indicator is flashing.
Tire Pressure Sensor Fault — The message center displays TIRE PRESSURE SENSOR FAULT when a TPMS sensor is malfunctioning.
No communication with the BCM — The TPMS warning indicator illuminates when the IPC has not received any signals from the BCM for more than 5 seconds. The message center displays TIRE PRESSURE MONITOR FAULT.
Tire Pressure Monitor Fault — The message center displays TIRE PRESSURE MONITOR FAULT when the TPMS is malfunctioning