Everything You Need to Know About Ignition Control Modules

An ignition control module (ICM) is a vital component of the ignition system in many internal combustion engines. It regulates the electric current that flows to the ignition coil or coils, which then generate the high voltage sparks that ignite the air-fuel mixture in the cylinders. Without a properly functioning ICM, your engine may not start or run smoothly.

But what exactly does an ICM do, and how can you tell if it is faulty? In this article, we will answer these questions and more. We will also give you some tips on how to test and replace your ICM if needed.

What is an ICM and How Does It Work?

An ICM is also known as an igniter or a control unit. It is usually located inside or near the distributor, which is a device that distributes the spark to each cylinder at the right time. Some vehicles may have the ICM mounted on the firewall or on the side of the engine.

The ICM receives signals from the engine management system, such as the crankshaft position sensor and the camshaft position sensor, which tell it when to charge and fire the ignition coil or coils. The ignition coil is a transformer that converts low voltage current from the battery into high voltage current that can jump across the spark plug gap.

The ICM acts as a switch that grounds and ungrounds the negative side of the coil, creating a magnetic field that builds up and collapses rapidly. This induces a high voltage pulse in the secondary winding of the coil, which travels through the spark plug wire to the spark plug electrode. The spark then ignites the compressed air-fuel mixture in the combustion chamber, producing power and exhaust.

What are the Symptoms of a Bad ICM?

An ICM can fail due to various reasons, such as overheating, moisture, corrosion, vibration, or electrical surges. A bad ICM can cause several problems with your engine performance and drivability, such as:

• No start or hard start: If the ICM does not send any signal to the ignition coil or coils, there will be no spark at all and your engine will not start. Alternatively, if the signal is weak or intermittent, your engine may start with difficulty or stall after starting.
• Engine misfire: If the ICM sends an incorrect or erratic signal to the ignition coil or coils, some cylinders may not receive enough spark or receive it at the wrong time. This will cause incomplete combustion and loss of power.
• Poor fuel economy: If the ICM causes your engine to run rich or lean, your fuel consumption will increase and your emissions will worsen.
• Check engine light: If your vehicle has an onboard diagnostic system (OBD), it may detect a problem with the ignition system and turn on the check engine light. You can use a code reader to scan for trouble codes that may indicate a faulty ICM.

How to Test an ICM?

If you suspect that your ICM is bad, you can perform some tests to confirm it before replacing it. You will need some tools and equipment, such as a multimeter, a test light, a spark tester, and a service manual for your vehicle.

Here are some steps you can follow to test your ICM:

1. Locate your ICM and disconnect its electrical connector.
2. Set your multimeter to measure resistance (ohms) and check for continuity between each terminal of the connector and ground. You should see infinite resistance (no continuity) on all terminals. If you see any continuity, your ICM is shorted to ground and needs to be replaced.
3. Reconnect the electrical connector and set your multimeter to measure voltage (volts). Turn on the ignition switch but do not start the engine. Check for battery voltage at one of the terminals of the connector (usually marked B+ or BAT). If you do not see battery voltage, there may be a problem with the wiring or the fuse.
4. Set your test light to the negative side of the battery and probe the other terminal of the connector (usually marked IGN or TACH). You should see the test light flash as the engine cranks. If you do not see any flashing, your ICM is not receiving or sending any signal and needs to be replaced.
5. Disconnect the spark plug wire from one of the spark plugs and attach a spark tester to it. Crank the engine and observe the spark tester. You should see a bright and consistent spark. If you see a weak or no spark, your ICM may not be charging or firing the ignition coil properly and needs to be replaced.

These are some basic tests you can do to check your ICM. However, different vehicles may have different testing procedures and specifications. You should always consult your service manual for more detailed and accurate information.

How to Replace an ICM?

If you have confirmed that your ICM is bad, you can replace it yourself or take it to a professional mechanic. Replacing an ICM is not very difficult, but it may require some time and patience. You will need some tools and equipment, such as a socket wrench, a screwdriver, a torque wrench, and a new ICM.

Here are some steps you can follow to replace your ICM:

1. Disconnect the negative battery cable to prevent any electrical shocks or shorts.
2. Locate your ICM and disconnect its electrical connector and any other wires attached to it.
3. Remove the mounting bolts or screws that secure the ICM to the distributor or the engine.
4. Lift the ICM out of its position and inspect it for any signs of damage or wear.
5. Clean the mounting surface and apply some dielectric grease to prevent corrosion and improve heat transfer.
6. Install the new ICM in place and secure it with the mounting bolts or screws. Torque them to the specifications given in your service manual.
7. Reconnect the electrical connector and any other wires to the new ICM.
8. Reconnect the negative battery cable and start the engine. Check for any leaks, noises, or codes.

These are some general steps you can follow to replace your ICM. However, different vehicles may have different replacement procedures and precautions. You should always consult your service manual for more detailed and accurate information.

Conclusion

An ignition control module (ICM) is an important part of the ignition system that controls the electric current to the ignition coil or coils. A bad ICM can cause various problems with your engine performance and drivability, such as no start, misfire, poor fuel economy, and check engine light. You can test your ICM with some tools and equipment, such as a multimeter, a test light, a spark tester, and a service manual. You can also replace your ICM yourself or take it to a professional mechanic. Replacing an ICM is not very difficult, but it may require some time and patience. You should always consult your service manual for more specific information about your vehicle.

We hope this article has helped you understand what an ICM is, how it works, how to test it, and how to replace it if it fails. If you have any questions or comments, please feel free to leave them below. Thank you for reading!