Ignition coil
Ignition coil — checking, measuring, faults
Here you will find useful basic information and important tips relating to ignition coils in vehicles.
The ignition coil generates the high voltage required to ignite the fuel/air mixture in gasoline engines. On this page you can find out how ignition coils work and which designs are used in the latest generation of vehicles, for example. You will also find a wealth of practical tips for diagnostics and checks on ignition coils.
Important safety note
The following technical information and practical tips have been compiled by HELLA in order to provide professional support to vehicle workshops in their day-to-day work. The information provided on this website is intended for suitably qualified personnel only.
TABLE OF CONTENTS
IGNITION COIL: BASIC PRINCIPLES
The design of a conventional ignition coil is basically similar to that of a transformer. The ignition coil's task is to induce a high voltage from a low voltage. Alongside the iron core, the main components are the primary winding, the secondary winding, and the electrical connections.
The laminated iron core has the task of amplifying the magnetic field. A thin secondary winding is placed around this iron core. This is made of insulated copper wire about 0.05-0.1 mm thick, wound around up to 50,000 times. The primary winding is made of coated copper wire about 0.6-0.9 mm thick, and is wound over the secondary winding. The ohmic resistance of the coil is around 0.2–3.0 Ω on the primary side and around 5–20 kΩ on the secondary side. The winding ratio of primary to secondary winding is 1:100. The technical structure may vary depending on the ignition coil's area of application. In the case of a conventional cylinder ignition coil, the electrical connections are designated as terminal 15 (voltage supply), terminal 1 (contact breaker), and terminal 4 (high-voltage connection).
The primary winding is connected to the secondary winding via a common winding connection to terminal 1. This common connection is known as the "economy circuit," and is used to simplify coil production. The primary current flowing through the primary winding is switched on and off via the contact breaker. The amount of current flowing is determined by the coil's resistance and the voltage applied at terminal 15. The very fast current direction caused by the contact breaker changes the magnetic field in the coil and induces a voltage pulse, which is transformed into a high-voltage pulse by the secondary winding. This passes through the ignition cable to the spark plug's spark gap and ignites the fuel-air mixture in a gasoline engine.
The amount of high voltage induced depends on the speed of change in the magnetic field, the number of windings on the secondary coil, and the strength of the magnetic field. The opening induction voltage of the primary winding is between 300 and 400 V. The high voltage on the secondary coil can be up to 40 kV, depending on the ignition coil.
1 Iron core, 2 Insulating compound, 3 Sealant, 4 Secondary winding, 5 Primary winding, 6 Cladding sheet, 7 Fastening clip, 8 Housing, 9 High-voltage spring contact, 10 Insulating cover, 11 Insulating material, 12 High-voltage output, A Terminal 15, B Terminal 4, C Terminal 1
Ignition coils for ignition systems with rotating high-voltage distribution
These cylinder ignition coils are used in vehicles with ignition distributors in contact-controlled or transistor-controlled ignition systems. The three-pin electrical connection corresponds to that of a conventional ignition coil.
The primary circuit receives its voltage supply through terminal 15. The contact breaker is connected to terminal 1 of the ignition coil, and supplies the primary winding with ground. The high-voltage wire of the ignition distributor is connected to terminal 4. Whereas conventional ignition coils are still being used with older vehicles, ignition coils with integrated electronic control units are now used in vehicles that are equipped with a transistor ignition.
Dual-spark ignition coils
Dual-spark ignition coils are installed in ignition systems with static high-voltage distribution. These ignition coils are used with engines with an even number of cylinders.
The primary winding and secondary winding of the dual-spark ignition coil each have two connections.
The primary winding is connected to the voltage supply at terminal 15 (plus), and to the output stage of the ignition or electronic control unit at terminal 1 (ground). The secondary winding is connected to the spark plugs with the outputs (4 and 4a).
In these systems, two spark plugs are supplied with high voltage by each single ignition coil. Since the ignition coil generates two sparks simultaneously, one spark plug has to be in the working cycle of the cylinder and the other offset by 360° in the ejection cycle.
In a four-cylinder engine, for example, cylinders 1 and 4 are connected to one ignition coil, and cylinders 2 and 3 to another. The ignition coils are triggered by the ignition output stages in the electronic control unit. This receives the TDC signal from the crankshaft sensor in order to begin triggering the correct ignition coil.
1 High-voltage connection, 2 Low-voltage connection, 3 Secondary winding, 4 Primary winding, 5 Iron core
1 Ignition control unit, 2 Ignition coil, 3 Spark plugs
Four-spark ignition coils
Four-spark ignition coils replace two dual-spark ignition coils in four-cylinder engines. These coils each have two primary windings, each of which is triggered by an electronic control unit output stage. There is only one secondary winding. There are two connections for the spark plugs at each of its outputs; these are switched contrarily using diode cascades.
1 Ignition control unit
2 Ignition coil
Single-spark ignition coils
In systems with single-spark ignition coils, one ignition coil with a primary and secondary winding is assigned to each cylinder. These ignition coils are usually installed directly at the cylinder head, above the spark plug.
These coils are also connected to the primary winding at terminal 15 (voltage supply plus), and to the electronic control unit at terminal 1 (ground). The secondary winding is connected to the spark plug at the output of terminal 4. If there is also a terminal 4b, this connection is used to monitor misfiring. Triggering takes place according to the sequence specified by the electronic control unit.
A single-spark coil's circuit corresponds to that of a conventional ignition coil. In addition to this, a high-voltage diode is used in the secondary circuit to suppress the "closing spark." This diode suppresses the unwanted spark produced when the primary winding is switched on as a result of the self-induction in the secondary winding. This is possible because the secondary voltage of the closing spark has opposite polarity to the ignition spark. The diode blocks in this direction.
For single-spark coils, the second output of the secondary winding is routed to ground via terminal 4b. A measuring resistor is installed in the ground wire to monitor ignition; this provides the electronic control unit with a measurement of the drop in voltage caused by the ignition current during sparkover.
1 Low-voltage connection, 2 Secondary winding, 3 High-voltage connection, 4 Spark plug, 5 Primary winding, 6 Iron core
1 Ignition control unit
2 Spark plug
IGNITION COIL FAULTY: CAUSE OF FAILURE
SYMPTOMS OF A FAULTY IGNITION COIL: SYMPTOMS
A fault can manifest itself as follows:
- Engine does not start
- Vehicle misfires
- Poor acceleration or loss of power
- Engine control unit switches to limp-home mode
- Engine warning lamp lights up
- Fault code is stored
MEASURING THE IGNITION COIL: BASIC PRINCIPLES
Dismantled state
There are different ways of checking the ignition coil:
Testing the resistance values of the coils using the ohmmeter.
Depending on the ignition system and ignition coil design, the following reference values apply: (observe the manufacturer's specifications)
Cylinder ignition coil (transistor ignition system)
Primary: 0.5 Ω–2.0 Ω/Secondary: 8.0 kΩ–19.0 kΩ
Cylinder ignition coil (electronic ignition system with map-controlled ignition)
Primary: 0.5 Ω–2.0 Ω/Secondary: 8.0 kΩ–19.0 kΩ
Single-spark or dual-spark ignition coil (fully electronic ignition system)
Primary: 0.3 Ω–1.0 Ω/Secondary: 8.0 kΩ–15.0 kΩ
Installed state
The following checks can be used:
Visual inspection
- Check the ignition coil for mechanical damage
- Check the housing for hairline cracks and sealant leaks.
- Check the electrical wiring and plug connections for damage and oxidation.
Check the electrics using a multimeter or oscilloscope
- Check the voltage supply to the ignition coil
- Check the triggering signal from the ignition distributor, ignition control unit, or engine control unit
- Illustration of the high-voltage curve using an oscilloscope or ignition oscilloscope
Testing with the diagnostic unit
- Read out the fault memory of the ignition system or engine control
- Read out parameters
During all testing work on the ignition system, please note that faults established during tests with the oscilloscope are not necessarily faults caused by the electronic system; they can also be caused by a mechanical problem in the engine. This may be the case, for example, if compression is too low in one cylinder, which means the oscilloscope shows the ignition voltage for this cylinder to be lower than that of the other cylinders.
NOTE
Although "diagnosable engine management systems" are installed in today's vehicles, a multimeter or oscilloscope must be used when checking ignition systems. In order to interpret the displayed measuring results and figures correctly, additional employee training is usually required. One important pre-requisite for successful diagnostics is a careful visual inspection at the beginning of the troubleshooting process.
CHECKING THE IGNITION COIL: TROUBLESHOOTING
We would like to demonstrate the diagnostics procedure for a dual-spark ignition coil using the following example, "misfiring".
Vehicle: Alfa Romeo 147 1.6 TS with dual-spark ignition
Each cylinder has a main plug and a secondary plug. The ignition coils are triggered by the ignition output stages integrated in the engine control unit. In this example, the repair procedure is shown using a Mega Macs diagnostic unit. The schematic illustrations, figures, and descriptions are intended solely as explanations of the document text, and cannot be used as the basis for carrying out installation and repair work.
Condition for diagnostics work: Engine mechanics, battery, starting system, and fuel system OK.
Customer complaint
- The customer has reported a functional problem with the engine control system
- Warning information on the instrument cluster:
Fault: Engine monitoring system.
Troubleshooting
Using the diagnostic unit
Connect the diagnostic unit to the 16-pin OBD connector. Depending on the vehicle manufacturer and date of registration, a different diagnostic socket and additional adapter may be required.
Carry out the following applications on the diagnostic unit:
- Select program
- Select vehicle
- Select fuel type
- Select model
- Select vehicle type
- Select required function
- Select system: Depending on which diagnostic unit is being used, additional safety instructions may be displayed here.
- Start fault diagnostics
Sufficient battery voltage and the correct connector are required in order to establish communications with the electronic control unit. Insufficient supply voltage to the electronic control unit could be an indication of a wiring defect or a defect in the vehicle battery.
Read out the fault memory
In this case, fault PO303 was stored.
- Combustion of cylinder 3
- Misfire detected in cylinder 3
Evaluate the details
Additional information on the possible fault causes
is saved here
- Ignition faulty
- Injection valve faulty
- Electronic control unit faulty
Note:
If several fault codes are displayed, clear the fault first. Once this is done, carry out a test drive with the diagnostic unit connected. Monitor the parameters and read out the fault memory.
Determine the fault cause
Preparations for engine diagnostics
- Prepare any additional diagnostic units that may be necessary, such as a multimeter or oscilloscope
- Find the technical documents
- Remove the engine cover (if present)
Carry out a visual inspection
Before the actual diagnostics process begins, the engine wiring harness and plug connectors must be checked for damage as far as possible. Kinks, lack of strain relief, and "marten bites" in the wiring harness are all possible causes of this.
Check voltage supply on the cylinder 3 ignition coil
- Remove the connector from the ignition coil.
- Measure the voltage at the two-pin connector on the wiring harness side
- Connect the red cable from the multimeter to PIN 2 (+), and the black cable to engine ground (-).
Switch on the ignition. A voltage of more than 10.5 V should be measured. Measured value: 11.93 V. Measurement OK.
Check the primary actuation of the cylinder 3 ignition coil
- Remove the connector from the ignition coil
- Connect the oscilloscope or diagnostic tester to the measurement module
- Connect the probe tips to PIN 1 and PIN 2 using the two-pin connector.
- Detach the plug connectors from the injection valves.
- Start the engine
A signal must be clearly identifiable on the oscilloscope.
In this example, the measurement is successful.
Remove the ignition coil for further tests
- Remove the connector from the ignition coil
- Remove the high-voltage cable for the second spark plug
- Remove the fixing screws
- Pull the ignition coil out vertically, keeping it parallel to the plug slot
In order to avoid damaging the spark plug connector, it
is essential to avoid rotating the ignition coil.
Measure the resistance
Use the multimeter to check the removed ignition coil. Connect an ohmmeter directly to the component connector PIN 1 and PIN 2 in order to measure the primary winding.
- Reference value: 0.3 Ω–1.0 Ω
- Actual value: 0.5 Ω (OK)
In order to measure the secondary coil, measure the probes directly at the
high-voltage outputs of the ignition coil.
- Reference value: 8.0 kΩ–15.0 kΩ
- Actual value: ∞ (interruption in secondary coil)
In this context, please always observe the
vehicle manufacturer's specifications.
Replace the ignition coil
Here, care must be taken that the spark plug connector and the high-voltage cable for the second plug fit properly. Attach the ignition coil using the fixing screws. Once this is done, insert all the plug connections for the ignition coil and the injection valve connectors.
Clear the fault memory
During the diagnostics work, additional faults were detected by the electronic control unit. These must be cleared before the test drive.
Check the function
Carry out a test drive with the diagnostic unit connected. Once this is complete, read out the fault memory again.
Note
Always take the vehicle manufacturer's specifications into account during all testing and diagnostic work. Depending on the manufacturer, additional vehicle-specific testing methods may have to be taken into consideration.
Safety instructions
During work on electronic ignition systems, contact with live components can result in potentially fatal injuries. This applies not only for the high-voltage live secondary circuit, but also for the primary circuit. For this reason, testing and repair work should only be carried out by trained specialist staff.
Please observe the following safety measures:
- Do not touch or remove ignition cables, the distributor cap, or the spark plug connectors when the engine is running
- Only connect or disconnect electronic control units, plug connections, and connection cables when the ignition is switched off.
- Only wash the engine when the engine is at a standstill and the ignition is switched off.
- During all tests on the ignition system that require the engine to turn over at starter speed, the voltage supply to the injection valves should be interrupted in order to protect the catalytic converter.
IGNITION COIL TROUBLESHOOTING TREE: INSTRUCTIONS
Troubleshooting tree for ignition coil with integrated ignition control unit (ignition module)
Example: VW/engine code APQ, Motronic MP 9.0. Pre-requisite for diagnostics work: Engine mechanics, battery, starting system, and fuel system OK.
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