What does it mean?
OBD II fault code P0237 is a generic code that is defined as ”Manifold absolute pressure (MAP) sensor “A”, TC system low input”, and is set when the PCM Powertrain Control Module) detects an abnormally low reading from the turbocharger boost pressure sensor. Note that on some applications, the turbocharger boost pressure sensor and its circuit may be labelled with a letter other than “A”, since there is no set rule or convention regarding the labelling of sensors.
On most applications, the turbocharger boost pressure sensor is a pressure sensitive sensor whose resistance changes as the boost pressure changes. This sensor is usually supplied with a 5-volt reference voltage by the PCM; as the boost pressure changes, the resistance of the sensing element changes in direct proportion to the change in pressure.
The changing resistance causes more or less current to pass through the sensor, which changes in the reference voltage are then transmitted back to the PCM via a dedicated signal circuit. The PCM interprets the signal voltage as pressure, and should the signal voltage fall below a predetermined minimum allowable value, the PCM recognizes that it cannot control the boost pressure effectively, and it will set code P0237 and illuminate a warning light as a result.
Note that in the case of code P0237, the minimum allowable pressure value is usually 9 PSI (or more) less than the minimum allowable value set by the manufacturer.