Limp-In Mode - What happened to your foot. No it's the car idiot...

Limp in mode is when the ECM reverts to the basic injection pattern due to a major problem just to allow the driver to reach the nearest repair shop. Often, this mode is seen as the actual fault, as in the engine lacks power, but it really is an end result or symptom of the real fault. See it here.

 

THEORY OF OPERATION

Limp-home or fuel backup mode is activated for the benefit of the driver, in order for him/her to reach the nearest repair shop. This mode allows the engine to run only on the RPM and TPS or MAP/MAF inputs. No fuel control system can run on only one signal input alone. The RPM (CRK sensor or pick-up coil) input always has to be present and it is the most important signal on any vehicle. Without it, the ECM can not trigger the injectors and fire the ignition coil (s). The second input for the engine to run involves a way for the ECM to know the amount of air intake. Either the TPS or MAP/MAF sensors are capable of detecting this. With those two inputs alone the system can operate, albeit, with reduced power and no regards for emission control. The system simply looks at engine speed (RPM), air intake (TPS or MAP) and infers the rest from the look-up tables stored in ROM memory. As said before, the idea is to let the driver reach the nearest repair shop.

Limp-in mode can also be deduced if the scanner fuel-status parameter is stuck in open-loop.

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