Ignition Coils

The electronic ignition system is fitted with two twin tower coils which are directly driven by the ECM. The ignition coils are mounted on a bracket fitted to the rear of the engine. The circuit to each coil is completed by switching within the ECM, allowing each coil to charge. When the ECM determines the correct ignition point, it switches off current supply to the coil which in turn causes the magnetic field around the coil's primary winding to collapse, inducing ht voltage in the secondary winding and in the iron core of the coil. High tension voltage, of different polarities, is produced at either end of the coil's core and is transmitted to two cylinders simultaneously, one on compression stroke, the other on exhaust stroke. This is called the wasted spark principle.

Note that coil 1 feeds cylinders 1 and 6, coil 2 feeds cylinders 5 and 8, coil 3 feeds cylinders 4 and 7, and coil 4 feeds cylinders 2 and 3. The resistance of the spark plug in the compression cylinder is higher than that in the exhaust cylinder and hence more spark energy is dissipated in the compression cylinder. Coil failure will result in a lack of ignition, resulting in a misfire in the related cylinders. The fault is indicated by illumination of the malfunction indicator light (MIL) on North American specification vehicles.

The positive supply to the coils is fed via a common fuse and ignition relay located in the engine compartment fusebox. Each coil supply feed has an RFI suppression capacitor fitted adjacent to the coil mounting bracket. The ignition primary wires are screened to suppress the emission of radio frequency interference, with the screens being grounded at a connection on the ECM.


WARNING: The ignition coils operate at very high voltages, do not attempt repair operations and procedures on the ignition high tension / secondary system when the engine is running.


The ECM calculates the dwell timing from battery voltage and engine speed data to ensure sufficient secondary (spark) energy is always available without excessive primary current flow, thus avoiding overheating or damage to the ignition coils.

The spark timing for each individual cylinder is calculated by the ECM using an internal memory map under consideration of the following inputs:
- Engine speed
- Engine load
- Engine temperature
- Knock control
- Automatic gearbox shift control
- Idle speed control

The nominal value for a warm engine at idle is 12° BTDC


CAUTION: Avoid running the engine if there is a possibility of the secondary (ht) becoming open circuit. This condition could damage the ignition power stages and/or the ignition coils through excessive energy being reflected back into the primary circuit.


NOTE: Testbook is not able to perform diagnostics to the primary power stage coils. Ignition related faults are monitored indirectly via the misfire detection system and its fault codes (NAS vehicles only).


Resistance measurements of the primary and secondary sides of the ignition coils can be performed using a suitable multimeter. Default values are:
- Nominal primary coil resistance (up to 99MY) = 0.8 ohms
- Nominal primary coil resistance (from 99MY) = 0.5 ohms ± 0.05 ohms at 20° C (68° F)
- Nominal secondary coil resistance = 13.3 k Ohms ±1.3 k-ohms at 20° C (68° F)

If an ignition coil should fail, the following symptoms may be observed:
- Engine will not start - loss of spark
- Engine misfire on specific cylinders

An ignition coil failure is likely to occur for the following reasons:
- Connector or harness fault
- Coil open circuit
- Short circuit to vehicle battery supply or ground
- Faulty component