Motronic ME 7
Barometric Pressure (BARO) Sensor
F96 (1.8Turbo, M7.5.1)
Turbocharger RecirculatingValve
N249 (1.8Turbo, M7.5.1)
TheBARO Sensor F96 is mounted internally within
the Motronic ECM J220.
Previous Motronic M5.9.2 systems used a charge
pressure recirculating valve operated by intake
manifold vacuum. The key to its functionality was a
fully closed throttle valve allowing full engine vacuum
to operate the valve.
BARO Sensor F96 is used in conjunction with the
Charge Air Pressure Sensor G31 for charge pressure
control.
Electronic throttle control may not allow for this under
certain operating conditions. The throttle valve may be
held partially open for emissions purposes.
In higher elevations, charge pressure is reduced to
prevent overspinning the turbocharger.
BARO Sensor F96 is also used for fuel mixture
control, leaning out the short term fuel trim with
increasing altitudes.
Turbocharger Recirculating Valve N249 is used to
provide vacuum to the recirculating valve using
vacuum from a reservoir. This allows the ECM to
more accurately control turbocharger performance
during throttle transition.
Substitute Function
If BARO Sensor F96 fails, boost is limited to a safe
level, and power levels are reduced. Cold running fuel
adaptation no longer takes place.
Operation
N249 is a solenoid valve (see Glossary) similar in
design to others used in the engine management
system. Power is supplied via the fuel pump relay and
the Ground is switched by the ECM.
On Board Diagnostic
The ECM recognizes implausible signals, as well
as short circuit to Battery + and Ground. The fault
displays “Control unit defective.”
Substitute Function
The system is designed so that if N249 fails, the
recirculating valve will continue to function by
manifold vacuum.
On Board Diagnostic
The ECM recognizes short to Battery + and short
circuit to Ground.
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