Limp mode is activated when a car's performance is reduced due to abnormal sensor readings, improper mechanical operation, or low fluid levels which are designed to protect the engine and transmission. Common causes of limp mode include low transmission fluid or oil levels, malfunctioning sensors such as MAP, MAF, speed, or TPS sensors, worn out spark plugs or coil packs, failed fuel injectors, damaged wiring from debris, heat or leaks, or a failed transmission or clutch due to improperly adjusted linkages or damaged solenoids. Determining the exact cause can be difficult, so seeking help from an automotive repair shop is recommended to avoid further damage.