Manifold air pressure
Charge pressure sender G31
Part number 078 906 051
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. 1.88 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 2.559 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 or similar to Bosch Motorsport 0 281 002 205
MPX4250A
VOUT = VS (P × 0.004 - 0.04) ± (Pressure Error × Temp. Factor × 0.004 × VS) VS = 5.1 V ± 0.25 VDC
Bosch Motorsport
- 0 281 002 205: 0.2-2.5 bar
- ? ??? ??? ???: ?.?-2.5 bar (078 906 051 - Audi 2.7t)
- 0 281 002 401: ?.?-3.0 bar (038 906 051 C - Audi TTMKII/VW Jetta V TDI)
- 0 281 002 244: 0.5-3.5 bar
- 0 281 002 316: 0.5-4.0 bar
- 0 281 006 060: ?.?-4.0 bar (03K 906 051)
References
- AW discussion on MAP sensor function