Ignition Control

Courtesy of VOLVO CARS CORPORATION

The following components are used for ignition control:

• engine speed (RPM) sensor (7/25)
• Mass air flow sensor (7/17)
• Engine coolant temperature sensor (7/16)
• throttle position sensor on the electronic throttle unit (6/120)
• knock sensor (7/23)
• Transmission Control Module (TCM) (4/28)
• spark plugs with ignition coils (20/3-6)

The Engine Control Module (ECM) calculates the optimum ignition advance based on the software and information from the sensors. The Engine Control Module (ECM) cuts the current to the ignition coil mounted on the cylinder to be ignited and produces a spark.

During the starting phase the Engine Control Module (ECM) produces a fixed ignition setting. When the engine has started and the vehicle is being driven, the Engine Control Module (ECM) calculates the optimum ignition setting, taking factors such as the following into account:

• engine speed (RPM)
• load
• temperature

The Engine Control Module (ECM) analyses the signal from the knock sensors (KS) when the engine reaches operating temperature. If any of the cylinders knock, the ignition is retarded for that specific cylinder until the knocking ceases.

Before the Transmission Control Module (TCM) is going to shift, sometimes it sends a request for torque limitation to the Engine Control Module (ECM). This lowers the ignition momentarily to reduce the torque and thus give smoother shifting and reduced load on the transmission.

Lowering of ignition can be done in several levels, where the levels depend on the signals from the Transmission Control Module (TCM). The return signal from the Engine Control Module (ECM) to the Transmission Control Module (TCM) confirms that the signal reached the Engine Control Module (ECM).