The engine code C1123 is the main thing to check or to verify the process of the VCT solenoid. You are looking for a stabbing or stuck VCt solenoid valve produced by corruption. The C1123 engine code is somewhat a kind of chassis problem. The general meaning of the code is C for Chassis Code Problem is controller area network wiring bus and modules. 1 for MFG – Manufacturer Specific. 1 for Transmission. 2 for Air Conditioning (A/C) Clutch Feedback Circuit High Voltage and 3 for Transmission Control Module Reprogrammable Memory. Get the manual of the car and study to get the correct information.