Permanent Code But No Check Engine Light – How to Fix This?

If you can read a code with a scanner but don't see the check engine light on the dash, the code is not that important or it's a permanent code that will clear itself without your help when the ECU makes sure the problem has been solved.

Code but no CEL highlights

• Difficulty level:Medium
• Needed scan tools:Basic will do well
• Additional equipment:Good app will help
• Timeneeded:15-20 minutes
• Price in a shop:$150 - $250
• DIY repair:Depends on the code

Why does my scanner show codes but there is no check engine light?

Check engine light is there on your dash to show you some critical problems with your vehicle. There are a couple dozen of factors that can trigger the CEL and scare you to death if you have never been in such a situation before.

But it doesn't mean that any problem in your car will be accompanied by the check engine light. This light mostly goes on when there is a problem with the powertrain - mainly with the engine, emission system, and transmission. In all other cases, the codes may not reveal themselves until you scan the car with the help of OBD2 equipment.

If your scanner shows codes but the check engine light is not on, there are several possible explanations for why this happens:

• the codes are pending, so there is a problem but it's not critical for your engine, the ECU understands that some part or sensor of your engine system is malfunctioning, but for now, it doesn't lead to dangerous conditions;
• the codes are permanent, so you've already repaired the problems and the ECU holds this code just to check that everything is OK - it will need some time to gather more information and eventually clear the code;
• the codes are not connected to the powertrain - they may be different codes that tell you about electrical problems, issues with some safety systems, etc.
• the CEL malfunction - maybe your check engine light is just broken and doesn't go on when there is an actual problem with the engine, but such situations are extremely rare.

So, you should know that not all trouble codes that are registered in the ECU may trigger the check engine light. Even more, some critical codes don't always trigger the check engine light until the problem becomes threatening.

One example of a pending code is when your engine temperature sensor sends readings that are 10% higher or lower than normal. This is a serious issue because changing engine temperature may easily kill it in the end. But the 10-15% decline is thought to be OK. In this case, the ECU will register a pending code and will observe the situation further without bothering you with the check engine light.

Once the temperature sensor reads 15% lower or higher temperature than optimal, you will get the CEL on the dash. Or if the problem continues for some time, the check engine light will likely be on, too. But if the temperature readings go back to normal, the code will be cleared automatically.

Permanent codes - how can you clear them?

Both pending and permanent codes most often can't be cleared with all-purpose scanners. Some professional scanners can do this, but the code will reappear once the ECU gathers all the needed information.

Both these codes clear automatically after the problem is solved. Actually, we are surprised by how eagerly American drivers try to fight with different lights and codes instead of fighting against the problems that triggered those codes.

Here's what you should do to clear the permanent code:

• identify the code and check the unit that it reports about;
• check the unit that is potentially faulty and triggers the code;
• make sure there is a problem because DTC ad PDTC codes are not reliable sources of information;
• after that, replace the faulty unit (or clean it, or do anything else to make it work properly);
• drive your car for a while and then check if the code is still there;
• you may need to drive for quite a long time and take your car to different road conditions to defeat such a code.

So, just clearing it with a scanner is not an option. Even if your scanner is good enough to clear permanent codes, this code will most likely reappear once you start the engine. Also, I really don't understand why you need to clear the permanent or the pending code. It doesn't trigger the check engine light and doesn't send your engine to limp mode - it's invisible and doesn't bother you, so let it just do its job and then calmly go away.

Pending and permanent codes are very helpful for mechanics. When they use OBD2 scanners, they may get additional information on potential issues and check the units that can trigger those codes. It means they can better inspect your vehicle and find all possible issues with it to repair it.

Analyzing the permanent or pending trouble code in the ECU

These codes often look just the same as simple error codes that trigger the check engine light. So, you can just google the code and see what it means. When you are googling a trouble code that you got from your car, don't forget to use the car brand name. Different manufacturers use various systems of error code architecture, so there may be some misunderstanding.

To analyze the permanent code, you need to do the following:

• write down the full code when you are scanning the vehicle;
• go online and google the code along with your car brand name;
• find some trusted forums or blogs that describe this code and its effects;
• see if the symptoms in your vehicle are the same;
• find out which unit is in charge of triggering this code;
• inspect the unit that is potentially faulty;
• use other methods to make sure the unit is broken;
• replace the broken part and restart the engine, let it work for a while;
• try clearing the codes with your scanner and see if it reappears;
• if it does, drive for a couple of days and see if it's still there after that time.

Permanent codes need proper clearing - by repairing the vehicle. Also, some codes may still be there even after several days when you repair the car. The vehicle should go through all kinds of driving conditions for the ECU to gather all the needed stats and eventually clear this code.

This doesn't mean that if the code is there permanently, you shouldn't worry. If you repaired the car and in one month, see this permanent code again, something is wrong. Most likely, the diagnosis was incorrect and the problem is still there. Just investigate more what this code may mean and find the best solution for it.

Should you worry when you see trouble codes that you can't clear?

The moment when you accidentally find several trouble codes when scanning your engine just for fun is not the best second in your life. You may think that the car is broken and needs instant repair.

But no, if you don't see the check engine light, the code is not that serious. Instead of the CEL, you may also see some text warnings when you turn on the engine or just randomly when you drive. Sometimes, drivers just don't pay attention to those warnings but it's a big mistake.

Any minor issue can grow into a fatal problem after some time. So, it's always better to find this problem as early as you can and to solve it immediately. And pending or permanent trouble codes are great helpers in the early diagnosis of a problem with your car.

So, no, you shouldn't worry much when you see such a code, but you should react and solve the issue as soon as possible to avoid bad consequences.

What if there is a ghost trouble code?

I also know about another type of trouble code - the ghost code. If this is the case, you will randomly see the check engine light but when you connect the scanner, there is no code. Or you may see the code regularly but sometimes when you scan the vehicle, there is no code.

In most cases, these codes are connected to software glitches but they may also be the consequence of a bad electrical contact in some sensor. It's important to identify such a code and investigate what can trigger it. After that, you will be able to quickly inspect the needed units and find the reason for these glitches to appear in your car.

Waiting for ghost codes to stop bothering you is not effective - they will only go worse after some time.