Check Engine Light Flashing But No Codes: Fixed!

Your check engine light is flashing and your vehicle has started shaking with intermittent rough idling. Moreover, some of you might have observed that the blinking check engine light went away for a few miles and then started flashing again.

A flashing check engine light means a misfire is occurring. If your check engine light is flashing but you don’t have any codes, it’s possible that your car is experiencing an intermittent problem. This means that the problem is not always present, and it may come and go. So, if the check engine light is flashing but no codes, you should check the fuel injectors, ignition coil pack and spark plug of each cylinder. If there are any signs of crud, damage or burning oil on the spark plugs, you should replace them.

Causes Of Check Engine Flashing But No Codes

Here are some of the most common causes of check engine light flashing but no codes.

1. Check Engine Light Is Flashing Intermittently

If your car is giving a flashing check engine light at times, the chance is that your vehicle’s computer has set the code but when the flashing check engine light went away, the code was cleared, due to which your OBD2 scan tool couldn’t detect the trouble code. There can also be pending trouble codes, which means that 

Some old scanners can’t detect any pending trouble codes or those diagnostic trouble codes that are stored in the history. I found the OBD2 scan tool by BlueDriver quite functional as it reads confirmed trouble codes, history trouble codes and pending trouble codes.

A pending trouble code is usually set when the vehicle’s computer detects a problem with the engine but not to the point that a fault actually exists. A pending trouble code during a flashing check engine light can also mean that a random misfire may occur typically less than three times.

History trouble code means that a vehicle experienced a serious intermittent misfire that threw a trouble code, but the misfire is not currently occurring.

As an example, if you hit a bump while driving, it could cause a spark plug to move or a wire to wiggle the wrong way and prevent the spark plug from getting a great connection. As a result, a misfire would occur for a few seconds which would cause a pending trouble code. At this point, a flashing check engine light might occur for some time then it goes away.

Now, if you’re using a Bluedriver OBD2 scan tool to detect trouble codes that are causing a flashing check engine light, it will show pending/history trouble codes or confirmed trouble codes as I have shown in the picture below:

If the OBD2 reader still does not show a trouble code, you can try driving with the OBD scanner attached.

Usually, we scan the code by only turning on the ignition key and keeping the engine off. But, if the check engine light is flashing without any codes, I would suggest you start the engine and continue driving with the OBD2 code attached. This is because you need a certain amount of engine misfires in a drive cycle to set a trouble code. 

You can also check fuel pressure while keeping the engine ‘ON’ using a live data option on the BlueDriver OBD2 reader. Depending on the engine, the suitable fuel pressure is between 40 and 60 psi. If the fuel pressure is out of range, it can be a sign of a bad fuel pressure regulator.

2. Bad Ignition Coils, Distributor Caps or Coil Packs

If an ignition coil or coil pack fails, it will cause the engine to misfire. The engine management system will detect the misfire and trigger the check engine light. The check engine light will flash if the misfire is severe enough to cause damage to the catalytic converter.

The ignition coil or coil pack is an important part of your engine’s electrical system. It’s like a  transformer that steps up the low voltage from your battery to the high voltage needed to fire your spark plugs.

Inside an ignition coil are two sets of windings. The primary windings are made of thick wire and have relatively few turns. The secondary windings are made of thinner wire and have many more turns.

The low voltage from your battery is applied to the primary windings. This creates a magnetic field. When the current is suddenly interrupted (by the ignition switch), the magnetic field collapses. This collapse induces a high voltage in the secondary windings. This high voltage is sent to the spark plugs, where it jumps across the spark plug’s gap and causes the spark that ignites the air/fuel mixture in the engine. 

In engines, there are three types of configurations of ignition coils:

• Coil on plug (COP)
• Distributor
• Coil pack

In my guide on the check engine light flashing and car shaking, you can learn about the configurations of the ignition coil.

Coil on plug configuration is in modern engines. In this configuration, each spark plug has an ignition coil. There can be a hairline crack around the neck of COP where the spark plug inserts into the ignition coil. The fuel can leak from there and cause a misfire in that cylinder where the ignition coil is damaged. 

If your vehicle has an ignition coil pack instead of COPs, you should check the insulation of each wire that leads from the coil pack to the spark plugs. There should not be cuts or bends.

Note: You may also swap ignition coils one by one and find which ignition coil is the cause of an engine misfire.

In Chevys and some older vehicles, distributors are used. A distributor has one ignition coil that distributes voltage to each spark plug through the distributor cap. 

A distributor helps to ensure that the spark plugs fire in the correct order, and at the correct time. So, a bad distributor can also cause engine misfires.

Note: It is also a good idea to check the connector that is plugged into the ignition coil. The intermittent illumination of a flashing check engine light without codes might be due to a damaged connector of the ignition coil. You should check its insulation and make sure there is no moisture inside the connector.

3. Spark Plug Is Not Properly Seated Or Damaged

If the spark plugs are not seated correctly and torqued enough, the fuel/gas will leak through the engine cylinder. As a result, the ratio of the fuel in the air-fuel mixture is disturbed, which will cause the engine misfire and a flashing check engine light. In the owner’s manual of the vehicle, the torque requirement for a spark plug is mentioned. For instance, the torque requirement for tightening the spark plug in Toyota Yaris is 27 N.m. 

Note: You should be careful when working with a spark plug wrench. Its skewing can cause damage to the threaded connection of the spark plug. Moreover, if you exceed the tightening torque requirement of the spark plug, it will damage the thread connection.

You should also check the condition of the spark plugs. A spark plug can become fouled with oil, dirt, and other debris, and this can cause it to stop working correctly.

Another common reason for spark plugs to become bad is that they are not properly gapped. The gap is the distance between the electrode and the metal tip of the spark plug, and it is important that this gap is set correctly. If the gap is too small, the spark will not be able to jump the gap, and the engine will not run. If the gap is too large, the spark will be able to jump the gap, but it will be less likely to ignite the fuel in the engine. 

Another common cause of bad spark plugs is carbon buildup. As your car’s engine burns fuel, it produces carbon deposits. These deposits can build up on the spark plugs and prevent them from sparking properly. 

You should also check the insulated part of the spark plug. If it has signs of cracks, it means the spark plug is bad.

This PDF is quite helpful to understand the signs of a bad spark plug.

Moreover, BlueDriver company has also uploaded a very helpful video on its YouTube channel to diagnose engine misfires and fix a flashing check engine light.

4. Damaged Fuel Injectors

If the fuel injector is any of the engine cylinders is damaged, it will also cause engine misfires and flashing check engine light. Fuel injector is just like a control valve that is electronically controlled by the ECU (Engine Control Unit).

If the fuel injector injects too much fuel, it will foul the spark plugs and cause engine misfires. In my guide on car won’t start after replacing fuel injectors, I have explained how to test fuel injectors.

Like the ignition coil, also inspect each connector of the fuel injector. Check if the insulation of the connector cable is broken at some point.

The following Youtube video is quite helpful:

Final Thoughts

So, if your check engine light is flashing with no codes, you should check for any pending trouble codes in your OBD2 scan tool or try pulling the trouble codes while driving your vehicle and keeping the OBD2 reader attached. Next, you should inspect spark plug, fuel injector and ignition coil of each cylinder.