"Limp mode" or limp home mode is the term used to describe substitute programming used by various controllers when data supplied doesn't add up.

One example is the coolant sensor on the engine management system: if the readings vary in a way that can't be duplicated in nature (hot one moment cold the next, etc.)the controller substitutes a warm reading and changes many of the rules; such as aux fan operation, compressor control, etc. Older systems would read the temp sensor when it went wrong and the car would stall or run poorly with all the extra fuel that would be used for cold running.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician