Radio Frequency Interference (RFI)

Radio Frequency Interference (RFI) can be caused by:

• Video equipment has been found to cause Radio Frequency Interference (RFI) especially when the video and power supply lines are near the TPMS.
• Anti-theft alarms (even those installed by the dealership) have been found to create enough Radio Frequency Interference (RFI) to cause the TPMS to malfunction or lose considerable range. These anti-theft 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 Radio Frequency Interference (RFI). Vehicles with the power point closest to the Radio Frequency (RF) receiver are the most affected. Most cell phone chargers do not produce high levels of Radio Frequency Interference (RFI) all the time, it depends on the state of charge of the cell phone battery. The phone battery must be almost completely discharged in some cases for the charger to produce enough Radio Frequency Interference (RFI) to interfere with TPMS operation.
• Power supplies and DC-to- AC inverters typically create Radio Frequency Interference (RFI). Most consumer grade equipment has very little filtering or shielding.

Using Hit Rate Parameter Identifiers (PIDs) to Determine the Presence of Radio Frequency Interference (RFI) 

If an intermittent Radio Frequency Interference (RFI) issue is suspected, the information contained in the last 5 TPMS warning event Parameter Identifiers (PIDs) can be combined with specific Parameter Identifiers (PIDs) from the BCM to determine which TPMS sensors are being affected and if a Radio Frequency Interference (RFI) source is currently present in the vehicle.

The BCM module contains Parameter Identifiers (PIDs) that keep track of the number of TPMS messages received from the 4 trained TPMS sensors. These Parameter Identifiers (PIDs) can provide insight on the performance of the TPMS, and can help establish the presence of an Frequency Interference (RFI) source.

• TPM_HITS_LF (Tire Pressure Monitor Hit Rate Left Front) - The number of TPMS messages received by the BCM module from the LH front sensor
• TPM_HITS_RF (Tire Pressure Monitor Hit Rate Right Front) - The number of TPMS messages received by the BCM module from the RH front sensor.
• TPM_HITS_LRO (Tire Pressure Monitor Hit Rate Left Rear Outer) - The number of TPMS messages received by the BCM module from the LH rear sensor
• TPM_HITS_RRO (Tire Pressure Monitor Hit Rate Right Rear Outer) - The number of TPMS messages received by the BCM module from the RH rear sensor.

Method for determining if a Radio Frequency Interference (RFI) issue has been affecting the TPMS:

1. Collect the last 5 TPMS events and determine if they were due to system faults or low tire air pressure.
2. Collect the TPMS Hit Rate PID counters and compare them to the last 5 TPMS events.
3. If the TPMS Hit Rate PID counters are significantly different from each other or if the locations with lower hit rate values show up as fault locations in last 5 TPMS events and BCM DTC B124D:02 (Tire Pressure Sensor: General Signal Failure) is present, an intermittent Radio Frequency Interference (RFI) source is most likely preventing the signals from these TPMS sensors from reaching the BCM.
4. An intermittent Radio Frequency Interference (RFI) source can also be the case when all 4 TPMS sensors show up in the last 5 fault events and BCM DTC B1182:00 (Tire Pressure Monitoring System (TPMS): No Sub Type Information) is present. The possible cause is most likely a strong source of Radio Frequency Interference (RFI) noise.

Original Equipment Manufacturer (OEM) Modules 

In some cases the Radio Frequency Interference (RFI) may actually be caused by a module or ground on the vehicle. Depending on the severity of the concern, 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 Radio Frequency Interference (RFI).

Using Customer Electronics to Pinpoint Radio Frequency Interference (RFI) 

This method can be a way to determine the cause of a concern before the sensors and module are replaced with little or no effect on system performance. Discuss with the customer what types of devices they were using when the event occurred. Determine which power points are being used and, if necessary, ask the devices be activated to determine their affect on the TPMS.

Options for Eliminating Intermittent TPMS Operation Caused by Radio Frequency Interference (RFI) 

• If an Original Equipment Manufacturer (OEM) component or customer device is causing a Radio Frequency Interference (RFI) concern, replace the device.
• If a cell phone battery charger is causing a Radio Frequency Interference (RFI) concern, the customer should consult with their cell phone provider to acquire a different battery charger.
• If a device such as a dealer installed anti-theft alarm is causing a Radio Frequency Interference (RFI) concern, 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 Radio Frequency Interference (RFI) source is present and cannot be moved or replaced, the intermittent concern remains. The TPMS must accept the unwanted system operation caused by the Radio Frequency Interference (RFI).