Possible Causes

WARNING: This page is about a different car, the 1999 Buick Regal and 1999 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.

Possible causes for DTC C1245 are as follows:

One tire is under inflated.
One tire is over inflated.
Tire pressures have been changed without resetting Tire Inflation Monitor (TIM).
Vehicle tires have been rotated without resetting Tire Inflation Monitor (TIM).

Conduct a thorough inspection of wiring and connectors. See INTERMITTENTS & POOR CONNECTIONS under DIAGNOSIS & TESTING.