Transmission is stuck in 4th gear and check engine light is on. Common cause?

No common cause possibly; staying in one gear is the default for "safe" mode to prevent further damage and get you to a safe place so the vehicle can have troubleshooting performed. Diagnostic trouble codes that have been set need to be reviewed to determine where to start looking to resolve the concern. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops