what can cause an error code C1203?

Question

The engine light turned on and that was the error after picking it up from a dealership.

Answer 1

C1203 ECM communication circuit malfunction

What should be check first is brake fluid level,a low brake fluid level switch can set this code ,the TRAC and VSC use this information for the skid control module, If the fluid is full you have a open circuit in the harness between the ECM to the skid control ECU.