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How to Tell if You Have a Bad Ignition Control Module

Mia Bevacqua
April 26, 2018

A faulty ignition control module can cause a number of problems.

1. Check engine light is on: The ECM monitors all parts of the vehicle that could affect emissions. This includes the ignition system. If it determines the ignition module has caused a problem with the system, it will turn on the check engine light.

2. Engine is misfiring or running rough: An engine misfire results from incomplete combustion. A faulty ignition module can affect ignition timing, resulting in an engine that misfires and runs rough. The engine may also run well at low speed, but won’t accelerate well.

3. Stalling: A failing ignition module can occasionally prevent the engine from getting spark, causing it to stall

4. Car won't start: An engine needs four basic things to run: fuel,compression, spark and exhaust. If the ignition module has failed completely, the vehicle won’t get spark and won’t start.

Continuing to drive with the symptoms mentioned above can damage your car’s catalytic converter. If you notice these symptoms, get your car checked out right away.

Get it diagnosed by a professional
 

What is the ignition control module?

These days, the vehicle’s main computer, the engine control module (ECM), is directly responsible for ignition control. But it wasn’t always that way. Up until around the turn of the century, that task belonged to the ignition control module. 

The ignition module is responsible for firing the spark plugs. Each spark plug must fire at exactly the right time for the engine to run properly. The ignition module uses input from the crankshaft position sensor or camshaft position sensor to determine when to fire the spark plugs. This is referred to as the vehicle’s base ignition timing. On most vehicles built within the last few decades, the sensor’s signal is sent first to the ECM. The ECM then uses this information to control ignition module operation.

On some vehicles, the ECM may control ignition timing above a certain engine RPM, while the ignition module has control below a certain RPM. In these instances, the signal from the sensor may first be sent to the ignition module.  

Engines with turbochargers, superchargers, split high velocity intake designs, variable valve timing or multi-fuel design capacity have more complex ignition timing systems to cope with the challenges these types of engines produce.

Advances in ignition technology are one of the most significant factors in the reliability we enjoy in the cleaner, more fuel-efficient cars we drive today.

» MORE: Get an estimate for your car repair

How to fix the problem

On some cars, the ignition module may be housed on or inside the distributor. In other cases, it may be a standalone unit, or it may be integrated into the ignition coil assembly. The ignition module is easy to access and replace on some vehicles, but on others, it’s buried deep inside the engine compartment.

Before spending time and money to replace the ignition module, a thorough diagnosis should be performed. A professional can do this using tools such as a spark tester, test light and a dedicated ignition module tester.  

Intermittent ignition failures can take extra time to diagnose, so it’s helpful if you can provide the technician with any clues to the problem, like “It wouldn’t start in the morning when it was cold, but I tried again at lunch and it seemed to run fine.” Finding the problem faster will save you money. 

 

Mia Bevacqua

About the Author

Mia Bevacqua is an automotive expert with ASE Master, L1, L2 and L3 Advanced Level Specialist certification. With 13-plus years of experience in the field, she applies her skills toward writing, consulting and automotive software engineering.

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