Check Engine Light Flashing And No Codes: Possible Causes and Solutions

Written By The Motor Guy

Certified ASE Master Automobile Technician

Last updated June 9, 2023

The check engine light is part of the warning system that notifies you of potential engine issues or emissions problems with your vehicle. When the check engine light flashes, it is usually a sign that something is wrong with your car that needs immediate attention.

Usually when the check engine light comes on, one or more diagnostic trouble codes are also stored in ECU memory. However, sometimes no codes are stored and this can be frustrating when it comes to diagnosing the cause of the issue.

One of the most common reasons for a flashing check engine light that doesn’t have any accompanying codes is an intermittent engine problem.

Sometimes, a problem may occur in the engine or emissions system that triggers the check engine light to flash but does not leave a permanent code.

These issues are detected by the onboard diagnostic system but do not immediately trigger a permanent code.

In this blog post, we will look at the reasons behind a flashing check engine light with no accompanying codes. We’ll explore some possible causes, discuss the importance of proper diagnosis, and provide insights on what steps you can take to address the issue.

What Causes A Flashing Check Engine Light And No Codes?

There are a few causes of a check engine light flashing without any diagnostic trouble codes (DTCs). These include intermittent faults that occur infrequently or do not leave a permanent code.

Electrical glitches and gremlins within the vehicle’s diagnostic system may result in a flashing light without any codes being displayed or sometimes there are pending codes that have been detected but not yet triggered a permanent code.

Sometimes there are codes stored but incompatible or malfunctioning OBD-II scanners can fail to retrieve these codes even though the check engine light is flashing.

Regardless of the absence of codes, it is crucial to address a flashing check engine light promptly as it signifies a significant problem.

Check engine light
A typical check engine light

The check engine light is a warning indicator on a vehicle’s dashboard that illuminates when the vehicle’s onboard diagnostic system (OBD) detects a problem with the engine, transmission, or emissions system.

When the check engine light illuminates, it means that there is an issue with the vehicle that needs to be addressed.

The OBD system usually stores a diagnostic trouble code that identifies the source of the problem. The trouble code can be read using a diagnostic scanner, which can help identify the issue and guide the repair process.

The check engine light does not always indicate a serious issue. In some cases, it may be a minor problem that can be easily fixed.

However, ignoring a warning light can lead to more serious issues down the road, so it is important to have the vehicle checked as soon as possible to rule out any potentially serious issues.

How Are Diagnostic Trouble Codes Linked To The Check Engine Light?

Diagnostic trouble codes (DTC) are linked to the check engine light because when the OBD system detects a fault or deviation from expected parameters, it generates a DTC that provides specific information about the nature and location of the detected problem.

The OBD system triggers the check engine light on the vehicle’s dashboard when a fault is detected, serving as a visual warning to the driver that there is an issue that needs attention.

The check engine light can indicate a wide range of issues, from minor problems to severe malfunctions that can cause significant damage to the vehicle if left unaddressed.

By linking DTCs to the check engine light, the OBD system helps drivers and technicians quickly identify and diagnose issues, guiding them in their troubleshooting process to address problems before they become more severe.

What Are Diagnostic Trouble Codes?

Diagnostic Trouble Codes (DTCs) are alphanumeric codes generated by a vehicle’s onboard diagnostic system when it detects a problem or malfunction within one of its systems or components. DTCs serve as a crucial tool in vehicle diagnostics, providing valuable information to mechanics, technicians, and vehicle owners about the specific issue that needs attention.

The importance of DTCs lies in their ability to pinpoint the source of a problem. When a check engine light illuminates, it indicates that a fault has been detected, but it doesn’t provide specific details about the underlying issue.

DTCs bridge this information gap by providing standardized codes that can be read and interpreted using an OBD-II scanner or diagnostic tool.

diagnostic OBD scanner
A mechanic using an OBD reader

Each DTC consists of a series of numbers and letters, such as P0301 or C0567, which correspond to a specific problem area or system in the vehicle. These codes provide a starting point for diagnosing the issue and guide the technician towards the affected component or system.

By retrieving and analyzing the DTCs, technicians can gain insights into the root cause of a problem and develop an appropriate repair strategy. DTCs help streamline the diagnostic process, reduce guesswork, and minimize the time and effort required to identify and resolve issues.

It’s important to note that DTCs alone do not provide a definitive solution to a problem. They are diagnostic aids that require further investigation and interpretation. Skilled technicians utilize their expertise, along with additional testing and inspection methods, to diagnose the issue accurately.

Understanding DTCs empowers vehicle owners and technicians alike to make informed decisions about repairs, maintenance, and overall vehicle health. By addressing the specific problem indicated by the DTC, it is possible to prevent further damage, improve vehicle performance, and ensure proper functioning of the vehicle’s systems.

What Are Pending Diagnostic Trouble Codes?

Pending Diagnostic Trouble Codes (DTCs) are codes that are stored by the vehicle’s onboard diagnostic system when a potential issue is detected, but the problem has not occurred frequently enough or met the specific criteria to trigger a permanent or “confirmed” DTC. Pending codes serve as preliminary indications of a problem that may require attention in the near future.

When a pending code is stored, it means that the vehicle’s diagnostic system has detected an irregularity or anomaly in a specific system or component.

However, until the problem is consistently detected during multiple drive cycles or reaches a certain threshold, it will remain as a pending code rather than a confirmed or active fault.

Pending codes can be helpful in diagnosing intermittent issues or early-stage problems that have not yet fully manifested. They provide valuable information to technicians during diagnostic procedures, indicating potential trouble areas that require further investigation.

It’s important not to overlook pending codes, as they can indicate developing issues that may eventually trigger a confirmed DTC and illuminate the check engine light.

To address pending codes, it’s recommended to monitor the vehicle’s performance closely and perform necessary inspections or repairs based on the specific code and associated symptoms.

Additionally, it’s advisable to consult the vehicle’s service manual or seek professional assistance to accurately diagnose and address the pending code to prevent any further complications.

Common Causes of Flashing Check Engine Light with No Codes

Here are some common causes of a flashing check engine light with no codes:

Intermittent Electrical IssuesFaulty electrical connections, loose wiring, or intermittent sensor malfunctions can trigger a flashing check engine light without generating codes.
Fuel Delivery ProblemsIssues with the fuel system, such as a clogged fuel filter, failing fuel pump, or fuel pressure irregularities, can cause a flashing light without specific codes.
Ignition System MalfunctionsFaulty ignition components, such as a malfunctioning ignition coil or spark plugs, can lead to a flashing check engine light without associated codes.
Engine MisfiresSevere or intermittent engine misfires can trigger a flashing check engine light, but if they occur infrequently or don’t meet the criteria for a code, no codes may be generated.
Emission System ProblemsFaulty or malfunctioning components in the emissions system, such as an oxygen sensor or catalytic converter, can cause a flashing light without specific codes.
Common Causes of CEL with no codes

One of the most common causes of a flashing check engine light with no codes is an intermittent electrical issue. This can be caused by a faulty ignition key, a blown fuse, a faulty PCM, or a transformer that is failing.

When these components fail, they can cause the check engine light to flash, but there may be no codes stored in the computer. Here are some other causes in more detail:

  1. Faulty Electrical Connections: Loose, corroded, or damaged electrical connections can disrupt the proper communication between various sensors, modules, or components in the vehicle. When these connections intermittently fail to provide accurate data or signals, the check engine light may flash as a result of the erratic or abnormal readings. However, if the issue is temporary and the connection is restored before a diagnostic scan is performed, no codes may be stored.
  2. Intermittent Sensor Malfunctions: Various sensors in the engine and emissions system play a crucial role in detecting abnormalities and triggering the check engine light. However, if a sensor intermittently malfunctions or provides inconsistent readings, it can cause the check engine light to flash without generating codes. The fault may not occur consistently enough during the diagnostic scan to trigger a code, making it difficult to pinpoint the specific problem.
  3. Wiring Problems: Frayed, damaged, or broken wires can lead to intermittent electrical issues. When the wiring is compromised, it can result in intermittent power supply or disrupted signals to various components, including sensors. As a result, the check engine light may flash intermittently without generating codes, as the fault is not consistently detected.
  4. Fuel Delivery Problems: Another common cause of a flashing check engine light with no codes is a fuel delivery problem. This can be caused by a faulty fuel pressure regulator, a clogged fuel filter, or faulty fuel injectors. When these components fail, they can cause the check engine light to flash, but there may be no codes stored in the computer.

It’s also possible for driver error to cause a flashing check engine light with no codes. For example, a faulty gas cap can cause the check engine light to come on, but there may be no codes stored in the computer.

How To Diagnose The Cause Of A Flashing Check Engine Light with No Codes

When a vehicle’s check engine light is flashing but there are no codes, it can be frustrating and confusing. However, there are diagnostic procedures that can be followed to determine the cause of the issue.

The first step in diagnosing a flashing check engine light with no codes is to use a professional diagnostic tool. A basic code scanner may not be sufficient to diagnose the issue, as it may not be able to read all of the vehicle’s systems.

An advanced scanner or an OBD2 scanner may be necessary to get a more complete picture of what is going on with the vehicle.

Once a professional diagnostic readout has been obtained, the following troubleshooting steps should be taken:

  1. Check the drive cycle: If the vehicle has not gone through a complete drive cycle, it may not be able to detect certain issues. A complete drive cycle involves driving the vehicle for a set amount of time at various speeds and under different conditions. Consult the vehicle’s owner’s manual for information on how to perform a complete drive cycle.
  2. Check the fuses: A blown fuse can cause the check engine light to come on and can also prevent the diagnostic tool from communicating with the vehicle’s systems. Check the vehicle’s owner’s manual for information on the location and function of the fuses.
  3. Check for Loose or Damaged Connections: Inspect the electrical connections related to the engine and emission control systems. Look for loose, corroded, or damaged connectors, wires, and harnesses. Ensure all connections are secure and free of debris. Faulty connections can cause intermittent issues that trigger a flashing light without generating codes.
  4. Monitor Symptoms: Pay close attention to any accompanying symptoms, such as engine misfires, rough idling, loss of power, or unusual noises. Note when the flashing check engine light occurs and under what driving conditions. Gathering specific details about the symptoms can help narrow down the possible causes.
  5. Conduct Visual Inspections: Perform a visual inspection of engine components, such as spark plugs, ignition coils, and vacuum lines. Look for signs of damage, wear, or leakage. Inspect the air intake system, including the air filter and intake ducts, for any obstructions or defects.
  6. Test Fuel System: Check the fuel system components, including the fuel pump, fuel injectors, and fuel pressure regulator. Verify that fuel delivery is adequate and that there are no blockages or leaks in the system.
  7. Inspect Emission Control Components: Examine the oxygen sensors, catalytic converter, and exhaust system for any signs of damage, contamination, or malfunction. Faulty emissions components can lead to a flashing check engine light even without codes.
  8. Scan with Advanced Diagnostic Tools: If the initial inspections don’t reveal the cause, consider using advanced diagnostic tools that can access additional data and perform more extensive tests. These tools, such as a professional-grade OBD-II scanner, can help retrieve enhanced trouble codes, view live sensor data, and perform system tests specific to your vehicle.
  9. Seek Professional Assistance: If you’re unable to identify the cause or lack the necessary tools and expertise, it’s advisable to consult a qualified mechanic or dealership. They have access to specialized diagnostic equipment and in-depth knowledge to diagnose complex issues accurately.


1. What is a false check engine light?

A false check engine light refers to a situation where the check engine light (CEL) illuminates on the vehicle’s dashboard, indicating a problem or fault, even though there is no actual issue with the vehicle. In other words, the CEL is triggered and remains lit when there is no legitimate reason for it to be on.
The check engine light can come on falsely due to various issues, including a loose or faulty gas cap, sensor malfunction, wiring or electrical problems, software or computer glitches, and instrument cluster malfunction. These issues can disrupt the communication between sensors, control modules, and the diagnostic system, leading to incorrect fault readings and a false indication. It’s best to have a qualified mechanic diagnose and repair the issue to avoid further damage to your vehicle.

2. Why is my car not throwing a code?

There are several reasons why a car may not throw a code, including intermittent issues that don’t occur during diagnostic scans, pending codes that haven’t fully matured into permanent DTCs, sensor thresholds not being exceeded, non-electrical issues that don’t generate codes, and a faulty OBD system that prevents codes from being stored or accessed.

3. Can car diagnostics be wrong?

Car diagnostics can be wrong due to several reasons, including faulty or outdated diagnostic equipment, human error, intermittent issues and software or computer glitches. While diagnostic tests can be helpful in identifying issues with a vehicle, they should not be relied upon solely for diagnosis. A qualified mechanic should also perform a physical inspection of the vehicle and conduct additional tests as necessary to ensure an accurate diagnosis.