Start/Stop, Specific Components
Battery Relay
Battery relay is only found on vehicles with the function automatic start/stop of engine.
The battery relay is a disconnector that disconnects the vehicle's battery and starter motor circuit from the rest of the electrical system during the time that the engine is restarted after an autostop. This is to prevent the low voltage, which briefly occurs when the starter motor is run, from propagating to the rest of the vehicle's electrical system. The secondary battery relay is also activated very shortly before the battery relay is activated. Then the secondary battery is connected and supplies the vehicle's other power users during the start phase. See also: Design: Secondary battery relay.
The battery relay is of the type 'normally closed' and can handle up to 150 A. The relay is connected to Engine control module (ECM).
The battery relay is diagnosed by the Engine control module (ECM). The output from the Engine control module (ECM) to the relay, the inner inductance in the relay's coil and the supply to the relay is diagnosed by the Engine control module (ECM). The relay's secondary side, i.e. the part of the circuit that is connected to the battery, is not diagnosed.
The battery relay is normally placed in a box in the cold area behind the engine together with the secondary battery. Some versions have these relays placed in the relay and fuse box between the battery and the front left wing.
For more information about the battery relay's function, see AUTOMATIC START/STOP OF ENGINE .
Secondary Battery Relay
Secondary battery relay is only found on vehicles with the function automatic start/stop of engine.
The secondary battery relay connects the secondary battery to the vehicle's electrical system during the time that the starter motor rotates, until the engine has been restarted after having been in autostop. Then the secondary battery supplies the engine's consumers except the battery and starter motor circuit, which are separated from the vehicle's electrical system via the battery relay. The secondary battery relay is activated shortly before the battery relay is activated.
The secondary battery's voltage is monitored by Central electronic module (CEM). When the battery needs charging Central electronic module (CEM) sends a request to Engine control module (ECM) to connect the secondary battery to the vehicle's electrical system. The battery is charged when the alternator charges and the secondary battery is connected. The time that the relay is activated depends on how much the secondary battery needs to be charged. When the engine is running (alternator charging) and the battery is connected to the vehicle's electrical system, the battery's voltage will be the same as the rest of the electrical system's voltage. If the battery is disconnected the voltage will be lower.
The secondary battery relay is of the type 'normally open' and can handle up to 70 A. The relay is connected to Engine control module (ECM).
The secondary battery relay can be diagnosed by Engine control module (ECM).
The output from Engine control module (ECM) from Engine control module (ECM) to the relay, the inner inductance in the relay's coil as well as supply to the relay are diagnosed by Engine control module (ECM). The relay's secondary side, that is, the part of the circuit connected to the secondary battery, is not diagnosed.
The secondary battery is placed by the battery relay. See battery relay.
For more information about the secondary battery relay's function, see AUTOMATIC START/STOP OF ENGINE .
Coolant Pump Relay
The coolant pump relay is only found on vehicles with the function automatic start/stop of engine without auxiliary heater as standard.
The function of the coolant pump's relay is to control activation and deactivation of the coolant pump. When the pump is active the coolant is circulated. In this way it is ensured that the engine's temperature can be kept within permitted limits when the vehicle is in autostop-mode.
The relay is of the type 3A and is normally open.
The coolant pump relay can be diagnosed by Engine control module (ECM). Outputs from Engine control module (ECM) to the coolant pump relay as well as the inner inductance in the coolant pump relay's winding are monitored with diagnoses by Engine control module (ECM).
The relay's secondary side, that is, the part of the circuit that supplies the coolant pump, is not diagnosed.
The coolant pump relay is located in the relay and fuse box in the engine compartment.
For more information about the coolant pump relay's function, see AUTOMATIC START/STOP OF ENGINE .
Brake vacuum sensor
The brake vacuum sensor is only found in vehicles with the function automatic start/stop of engine.
The sensor is a linear pressure sensor of analogue type and measures the underpressure in the brake booster. The engine control module (ECM) supervises the signal from the sensor by reading the voltage from the sensor output signal and turns this into a corresponding pressure. On some versions, the sensor is hardwired to the brake control module (BCM) which communicates the signal to the engine control module (ECM) over the CAN. The brake vacuum sensor is feed with voltage at 5 V and has its earthing to the engine control module (ECM). The output signal from the sensor can take on values between 0.5 and 4.5 V.
If Engine control module (ECM) registers a too low vacuum pressure during driving, activation of the function for automatic start/stop of engine will not be permitted (blocked autostop). If Engine control module (ECM) registers a too low vacuum pressure during the time that the function for automatic start/stop of engine is active (vehicle in autostop), then the function is cancelled and the engine is started automatically (system-requested autostart).
The brake vacuum sensor is located on the brake booster.
The engine control module (ECM) can diagnose the brake vacuum sensor.
For more information about the brake vacuum sensor's function, see AUTOMATIC START/STOP OF ENGINE .