Overrun mode fuel shutoff, function

Function requirements for deceleration fuel shutoff, general points

 Circuit 87 (Engine management ON)

 Engine runs

 Vehicle rolling

 Accelerator not operated

 Selector lever position "D" or "R"

 Vehicle not in cruise control or DISTRONIC PLUS mode (with code 233 (DISTRONIC PLUS))

Deceleration fuel shutoff, general

Deceleration fuel shutoff causes the drive wheels to transmit a braking torque to the engine via the transmission. This increases the braking effect of the engine (engine brake).

The CDI control unit (N3/9) performs a deceleration fuel shutoff depending on the following signals:

 Coolant temperature sensor (B11/4)

 Accelerator pedal sensor (B37), accelerator pedal position

 Crankshaft Hall sensor (B70), engine rpm

 Fully integrated transmission control unit (Y3/8n4) (with code 427 (7G-TRONIC) or (with code 421 (9G-TRONIC), gear range via the drive train CANC1)

Deceleration fuel shutoff, function sequence

If the accelerator pedal is not actuated (zero quantity delivery), deceleration mode is triggered. The CDI control unit switches off the fuel injectors (Y76) in deceleration mode dependent on the coolant temperature, the engaged gear and at an engine speed >1600 rpm.

The CDI control unit also lowers the fuel pressure in the rails over the pressure regulating valve (Y74). Upon operation of the accelerator pedal or a drop in the engine rpm to < 1600/min, the CDI control unit again actuates the fuel injectors and increases the fuel pressure in the rails over the quantity control valve (Y94) or the pressure regulating valve, dependent on the Model of regulation.

If the conditions for teaching in the injector zero quantities are fulfilled, the rail pressure can be increased in deceleration mode to up to 1000 bar.