Interesting reading. For as long as I have been working on cars, I never knew this. I don't recall seeing this information printed in any owners manual I have read. Wonder what the big secret is....

Causes of Check Engine Light Flashing
Reasons of check engine light blinking are different for each vehicle. But, a yellow or red light flashing is a serious cause of concern in itself, which is far more serious than a constant or steady check engine light. If you notice the light flashing when you drive the car in the city area, which goes off on a freeway, then you need to check for the overall performance of your vehicle in both the cases. If there is any problem in the performance and the mechanism of the car, then take the vehicle to the service center.

Engine Misfire
Check engine light flashing can be an indicator of misfire inside the car engine, which leads to catalytic converter damage, if not resolved soon. Along with the catalytic converter problem, check engine light blinking, can also be an indicator of a major problem in the emission control system of the engine. The emission control system consists of many active sensors that control the amount of pollutants, which are released by the vehicle. The flashing light can also be a denotation of dysfunctions in the oxygen sensors, which read the ratio of fuel and air inside the engine.

Spark Plug Wire
The aged spark plug wires become weak and brittle and lead to electric misfire inside the engine. Is your check engine light flashing and then getting steady, when you start the engine? If your answer is 'yes', then you need to turn off the engine immediately and check for the spark plug wires, using the OBD (on-board diagnostic) code. If the wires are worn out, then it is time to change them as soon as possible.

Loose Gas Cap
If the gas cap is not twisted correctly, then it can cause a check engine light flashing. In such cases, the check engine light blinking stops as soon as the gas cap is tightened. Sometimes, you may observe the light flashing or steady, for more than a day. In such situation, it is important to take the vehicle to the servicing center and let the experts determine the exact car problem.

It was from the ford dealership I used to work for. Everyone there had known about it.

Funny because I have had cars that actually had misfires (obd2 cars). Set a misfire code, but the check engine light never flashed on and off, just came on and stayed on. I've had shorted spark plug wires before. Never seen the light flash, only turn on and stay on until I cleared it. I wonder what the difference is to make the light flash as opposed to just setting a code for a misfire and turning the CEL on.

It's probably just an "Oh you're really eff'd now" light...haha :icon_biggrin:

Duplicate

Well what I was told is that it has to be bad enough to do damage. So it can miss reallt bad and not cause a flashing light untill a certain point. My guess would be the pcm has to see a certain number of mis in certain amount of time or a specific reading on the o2 sensors or both.

Years ago, I ran an engineering department that developed a lot of custom computerized systems for various applications & in the process in the process of development, you need to be able to test functionality & performance. To do a lot of this intermediate testing we used to develop various programs and circuits as tools to help in things like development debugging, proof of functional and performance correctness and many other things - these "tools" weren't always removed, but their functionality wasn't documented in manuals given for use by the customer, but they were documented and passed on to field service reps to help in tracing & repairing operational problems. I'm assuming that different PCM manufacturer's have different such test tools imbedded in the operational program and that this flashing indication could be one of them. As time goes on, some of these tools fall into disuse and their meaning becomes more obscure or forgotten.

'07 Dakota
 

My dad's '07Dakota just did this yesterday, while he was driving! It is idling high, around 12-1500 and is missing while driving. He has changed the spark plugs and the idle air control valve. This hasn't helped at all. Any ideas of what to try?

You need to read the OBDII codes.

He took it to O'Reilly's, and the code it gave was for the idle air control valve, which is why he replaced it, but it actually got worse after replacing it. He is calling the dealership today for an appointment, hoping he has better luck there, in the past the dealerships have been a complete joke and no help at all......he is the original owner and very precise with maintenance.