DTC C2121: TPM System Programming Malfunction: Description
WARNING: This page is about a different car, the 2000 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
DTC C2121 indicates receiver has been replaced and TPM sensors have not been programmed to new receiver. All TPM sensors and RKE transmitters must be programmed when receiver is replaced.
This DTC is automatically set at time of manufacture. No driver warning message will be displayed for DTC C2121. IPC will not display tire pressure data.
Receiver clears this DTC automatically when TPM sensor programming is complete.