Manifold air pressure

Charge pressure sender G31

The charge pressure sender is located upstream of the throttle valve control part.

The Motronic supplies the sender with a voltage of 5 volts and earth. The signal which the sender generates is a pressure-proportional voltage ranging from 0 to 5 volts.

At atmospheric pressure (14.7 psi or 1.01 bar at sea-level), the voltage is approx. 2.5 volts.

The signal is used for charge pressure control.

The Motronic also needs information on charge pressure so that it can take countermeasures if the maximum permissible pressure is exceeded.

The absolute maximum pressure reading is approximately 2.55 bar absolute (22.45 psi). Pressure readings that deviate more than ~500mbar from specified pressure may cause throttle cut.

Substitute function and self-diagnosis

If sender G31 fails, the charge pressure is controlled via the characteristic curve (engine speed-dependent). This will result in a deficiency of engine power.

Transfer function

The G31 is most likely a Motorola/Freescale MPX4250A.

VOUT = VS (P × 0.004 - 0.04)
± (Pressure Error × Temp. Factor × 0.004 × VS)
VS = 5.1 V ± 0.25 VDC

References

• AW discussion on MAP sensor function