Tire Pressure Monitoring (TPM) - Operation

OPERATION

The Tire Pressure Monitoring (TPM) system operates by monitoring a radio frequency transmission from the tire pressure sensor/transmitters located in each wheel, and integrated with the valve stem. When the vehicle reaches a speed of approximately 32 km/h (20 mph), centrifugal force created by the wheels rotating closes a roll switch inside each sensor, powering up the circuitry. To facilitate transmitting the radio signal to the TPM module, the valve stem acts as the antenna for the tire pressure sensor/transmitter.

The Body Control Module (BCM) monitors the tire pressure signal that is sent from the TPM module when the ignition key is in RUN/START position. When the BCM receives the tire pressure signal it will send a corresponding bus message to the cluster. If the BCM message indicates a fault, then the cluster will display in the odometer "LO TIRE" and send a chime request message to the BCM.

POWER UP INITIALIZATION

When the ignition is turned to RUN, the TPM output signal is grounded for 2 seconds, then goes open. If this sequence does not occur, then the BCM registers the Tire Module Initialization fault (DTC). Once this fault is matured (10 seconds), the BCM sends a bus message to the cluster. The cluster will display "LO TIRE" steady on and send a single chime request to the BCM.

TIRE DIAGNOSTIC FAULT

Once the RUN/START cycle and initialization of the TPM is complete, a tire diagnostic fault will be registered by the TPM if one or more tire sensors are not transmitting. These sensors start to transmit data after the wheel has reached a speed of approximately 32 km/h (20 mph). Because the BCM knows vehicle speed, it will mask this fault for 70 seconds after the vehicle speed is greater than 32 km/h (20 mph). Once this 70-second timer has elapsed, the BCM will monitor the TPM output for a diagnostic fault. If the TPM output is grounded for greater than three seconds, the BCM will start to mature the Tire Module Diagnostic fault and after 10 seconds, send a bus message to the cluster. The cluster will display "LO TIRE" steady on and send a single chime request to the BCM. If the fault has matured since the last ignition ON cycle, cycling the ignition switch will not clear the fault.

NOTE: If a tire is changed, the TPM must be reprogrammed or this fault will be set.

TIRE LOW PRESSURE

If the TPM module output toggles two (2) seconds low, then two (2) seconds open for 10 seconds, the BCM registers the Low Tire Pressure matured fault and sends a bus message to the cluster. The cluster will flash "LO TIRE" at a rate of two (2) seconds on and two (2) seconds off and send a single chime request to the BCM.

TIRE CRITICAL PRESSURE

If the TPM module output toggles one (1) second low, then one (1) second open for 10 seconds, the BCM registers Critical Tire Pressure matured fault and sends a bus message to the cluster. The cluster will flash "LO TIRE" at a rate of one (1) second on and one (1) second off and send a single chime request at the same rate to the BCM.

NOTE: Anytime the BCM identifies a faulted condition (send matured fault message to cluster), it will register a diagnostic trouble code (DTC).