Engine Ignition: Operation

WARNING: This page is about a different car, the 2018 Land Rover Discovery Sport. However, it is still accessible from the selected car via links, so may be relevant.

The ignition coils are supplied with electrical power from the Powertrain Control Module (PCM) relay in the Engine Junction Box (EJB). The PCM controls the operation of the PCM relay.

Each ignition coil has a 3 pin connector, which incorporates the following connections:

A power supply from the EJB by the PCM relay, through a 25A fuse.
A ground which allows the secondary winding to connect to ground.
A signal connection from the PCM, to control the ignition coil power stage switching (to open and close the primary circuit).

The PCM sends a separate signal to each ignition coil to trigger the power stage switching. The PCM calculates the dwell time from the startup battery voltage and engine speed. This provides a constant energy level, which is produced in the secondary coil each time the power stage is switched. Thus sufficient spark energy is available without excessive primary current flow, which avoids overheating and damage to the ignition coils.

The PCM calculates the ignition timing for individual cylinders from:

Engine speed from the Crankshaft Position (CKP) sensor.
Camshaft position from exhaust and intake Camshaft Position (CMP) sensors.
Engine load.
Engine temperature.
The knock control function.
The shift control function.
The idle speed control function.