Engine Control Module (ECM) (B5244S4; 2006-2007): Function: Start

Fig 1: Identifying Starter Motor Relay, TCM, ECM, Control Solenoid & CEM

Courtesy of VOLVO CARS CORPORATION

The starter motor (6/25) is powered via the starter motor relay (2/35). The relay is controlled by the engine control module (ECM) (4/46). The start process is as follows:

1. The ignition key is turned to start position (position III)
2. A high signal from the ignition switch (3/1) is transmitted to the engine control module (ECM) via the central electronic module (CEM) and integrated relay/fusebox in the engine compartment. The engine control module (ECM) interprets this high signal as a request to activate the starter motor.
3. The engine control module (ECM) activates the starter motor by grounding the relay for the starter motor relay. The relay is powered by the ignition switch
4. The relay closes the circuit between the starter motor solenoid and the battery, activating the starter motor
5. The engine control module (ECM) activates the starter motor until the ignition key is released from the start position (position III).

The starter motor will not be activated if:

• the function for electronic Immobilizer does not allow start. The engine control module (ECM) receives signal regarding if the electronic immobilizer is active or inactive, from the central electronic module (CEM) via the CAN-net.
• the gear selector is not in position "P" or "N" (automatic transmissions). The engine control module (ECM) receives a signal indicating the position of the gear selector from the transmission control module (TCM) (4/28) via both the controller area network (CAN) and from a directly connected cable between the engine control module (ECM) and transmission control module (TCM).
• the clutch pedal is released (manual transmissions, certain markets). The engine control module (ECM) receives a signal indicating the position of the clutch pedal from the central electronic module (CEM) via the controller area network (CAN).

Auto start (2007-) 

If the ignition key is released from position III before the engine is started, the starter motor continues to run. The starter motor runs until the engine is started or until after a certain amount of time. The engine coolant temperature (ECT) determines how long the starter motor is permitted to run:

• at -40 °C, approx. 10 seconds
• at -10 °C, approx. 8 seconds
• over 15 °C, approx. 4 seconds.

If the engine does not turn or if the engine speed is extremely low when the start relay is activated, the engine control module (ECM) interrupts start relay activation.

Activation of the starter motor is not permitted or is interrupted if:

• the engine is running (the engine speed (RPM) above a certain value)
• the immobilizer function does not allow a start
• the gear selector is not in position "P" or "N" (automatic transmissions). The engine control module (ECM) receives a signal indicating the position of the gear selector from the transmission control module (TCM) (4/28) via both the controller area network (CAN) and from a directly connected cable between the engine control module (ECM) and transmission control module (TCM).
• the clutch pedal is not depressed (manual transmission). The signal about the clutch pedal position (clutch pedal sensor) is received by the engine control module (ECM) (4/56), via the controller area network (CAN) and via a directly connected cable from the clutch pedal switch (3/271).
• the brake pedal is not depressed (automatic transmission).