When Monitored and Set Condition

When Monitored: With the ignition on, the Tire Pressure Monitor (TPM) monitors the tire pressure sensor/transmitters approximately once a minute (60 - 68 seconds) when the vehicle speed is above 33 km/h (20 MPH).
Set Condition: If the Tire Pressure Monitor (TPM) module receives a transmission from a tire pressure sensor/transmitter that the battery is low, the DTC will be set.

Fig 1: Identifying Possible Causes - Transmitter Failure

Courtesy of DAIMLERCHRYSLER CORP.