Description Of Causes For System Requested AUTOSTART [2014-2016, B4204T11 | 2014-2016, B4204T12]

GENERAL 

The Engine Control Module (ECM) detects and saves information about which causes have blocked the automatic start/stop of engine function and what has caused the system to request autostart in autostop mode. This document deals with causes of system requested restart.

HINT: If the Engine Control Module (ECM) and/or Central Electronic Module (CEM) detected a fault and stored DTCs for components/functions related to automatic engine start/stop, it is not certain that the occasion was stored as possible source. 

REQUEST AUTOSTART IN AUTOSTOP, BATTERY MONITORING 

Causes of system requested autostart in autostop:

• The power output/current from the battery, measured by the battery monitoring sensor, is greater than 60 A. Can be caused by, in autostop, large connected power consumers such as lighting, blower fan, radio, extra equipment (e.g. in the 12 V socket).

Checks:

• Check for large connected power consumers in autostop, such as lighting, blower fan, radio, extra equipment (e.g. in the 12 V socket).

REQUEST AUTOSTART IN AUTOSTOP, CLIMATE SYSTEM 

Causes of system requested autostart in autostop:

• The climate control system's blower fan runs too fast (current too high).
• Risk of misting on the windscreen calculated by the climate control module (CCM) from the signal from the humidity sensor.
• The engine coolant temperature in relation to the outdoor temperature is too low. A low coolant temperature at low outdoor temperatures can restrict the passenger compartment heating.
• The cooling demand is large (hot passenger compartment). The climate control module (CCM) uses the signal about the evaporator's temperature to calculate the cooling demand in the passenger compartment. If the cooling demand is too great, the climate control module (CCM) requests a system requested restart.

REQUEST AUTOSTART IN AUTOSTOP, BRAKE VACUUM 

Causes of system requested autostart in autostop:

• Incorrect pressure (vacuum too low) in the brake booster

Checks:

• Check the brake booster's function and non-return valve for air leaks. With the engine just shut off the vacuum in the brake booster should be enough for a few vacuum assisted brake attempts.
• Check for air leaks in the vacuum hoses between the brake booster and motor.
• Check that the vacuum pressure sensor works properly.

HINT: Read off the air pressure in the brake booster via VIDA/DIAGNOSTICS/VEHICLE COMMUNICATION/CEM/Parameters. 

REQUEST AUTOSTART IN AUTOSTOP, ENGINE MANAGEMENT SYSTEM 

Causes of system requested autostart in autostop:

• Engine coolant temperature becomes lower than +20 °C.
• The outdoor temperature becomes lower than 0 °C.
• Engine coolant temperature becomes greater than 100 °C.
• The engine coolant temperature is calculated to be too high. The engine coolant temperature is calculated by the Engine Control Module (ECM) from the vehicle speed, engine speed and the engine's torque.