Limp mode, default, or limp home mode are operational strategies programmed into the TCM of electronic transmissions to safeguard the engine and transmission from internal damage. Limp mode is different from most hard faults. ECMs illuminate the MIL or check engine light but leave the vehicle operational without limiting speed when a fault is detected.
Limp-in mode illuminates the MIL and operates the transmission in only one forward gear (2nd or 3rd) and reverse. The vehicle should be driven or towed directly to the repair shop because the mode causes the vehicle to start slow and the engine to rev high at speeds above twenty or thirty. An underlying condition has caused this, and an inspection and scan are needed to diagnose the fault that resulted in this condition.