Flat Tire Monitor System (FTM) - Diagnosis
SI B36 03 07Wheels and Tires
September 2007
Service Engineering
SUBJECT
Flat Tire Monitor System (FTM) Diagnosis
MODEL
E90 (3 Series) up to 3/07
E60, E61 (5 Series except M5) up to 3/06 E60 (M5) up to 9/06
E63, E64 (6 Series except M6) up to 3/06 E63, E64 (M6) up to 9/06
E65, E66 (7 Series) from 10/03 up to 3/06 E83 (X3) up to 3/06
E53 (X5) from 9/03
E85 (Z4) up to 1/06
INFORMATION
Flat Tire Monitor Systems are designed to alert drivers of sudden changes in tire pressure that can affect vehicle handling. The use of FTM or Tire Pressure Monitor systems does not eliminate the need for routine maintenance by the vehicle operator. BMW recommends checking tire pressures at least every two weeks and before long trips. FTM works in conjunction with the wheel speed sensors used by the ABS/ASC/DSC system. The comparison of wheel speeds can be used to calculate changes in a tire's rolling circumference. When the change in the wheel speed signal exceeds a predetermined value, a warning light is illuminated to inform the driver of a change in tire pressure.
The following points should be considered when diagnosing a report of a tire warning light:
^ After replacing a tire, the tire warning light may be illuminated although no change in pressure has occurred. The warning is a result of slight changes in a tire's rolling circumference that is associated with the tire assuming its normal operating shape after being mounted on a wheel. A new tire can expand after being operated through several drive cycles. Therefore, customers should be informed that the warning light may be illuminated after tire replacement. This would be a one-time occurrence and customers should verify correct inflation pressure and reset the FTM.
^ Check for proper inflation pressure of all four tires. Always document tire pressures when addressing complaints related to tires or tire monitor systems. Proper inflation pressures are listed on a label on the driver's doorjamb and in the vehicle's Owner's Manual. Tire pressures that are set incorrectly may cause a warning; this is a normal function of the system.
^ Visually inspect the tires installed on the vehicle. Note the tire brand, model and size for all four tires. Tires that are not the correct size or tires that have too much deviation in rolling circumference may cause false warnings. Additionally, tires that are worn out can cause false warnings. BMW recommends replacing tires that have reached a tread depth of 3 mm. Tires that are at or below the tread wear indicator limits should be replaced. A tire that has been worn to its limit may no longer provide adequate traction that can lead to a reduction in overall vehicle handling.
^ Perform a Short Test using the DISPlus or GT-1. Faults related to the steering angle sensor, wheel speed sensors, or other vehicle systems can cause the tire warning light to be illuminated. To ensure proper operation of the FTM, any related faults for other vehicle systems should be corrected.
^ Using the DISPlus or GT-1, check for the initialization data that is stored in the DSC module. The last initialization and the last warning can be displayed and should be checked before any attempt to reset the system.
^ If no cause for the tire warning light can be determined (incorrect tire pressure, mismatched tire sizes, relevant fault codes, etc.), the wheel speed signals should be checked using the scope function of the GT-1.
WARRANTY INFORMATION
Information Only