In this guide, we explain what Audi check engine light means, go over the common problems that trigger the Audi Check Engine Light (CEL).

You will also find step-by-step instructions on how to read Audi check engine light codes yourself using an OBD-II scanner. 

Symptoms

Here are a few things you may notice when your Audi check engine light turns on.

• Check engine light flashing and engine shaking
• EPC and check engine light come on
• Reduced engine power
• A decrease in fuel economy
• The vehicle goes in limp mode
• Check Engine Light with the lightning bolt comes on

If the problem is less serious, you may not notice any symptoms at all except the check engine light on. Even if you don't notice any symptoms, diagnose your Audi as soon as possible.

What Does Audi Check Engine Light Mean? 

If your Audi check engine light stays on, it means the On-Board Diagnostic (OBD) system has detected a problem. Fault codes often referred to as Diagnostic Trouble Code or DTC gets stored in the Engine Control Unit (ECU).

The problem could be emissions-related such as a loose gas cap but it can also be an indication of a serious problem such as a faulty transmission valve body. 

If your Audi check engine light comes on and there are no other symptoms, the first thing that you should do is tighten the gas cap.

 If your Audi check engine light doesn't reset within three to four days, it is time to read the codes.  See the instructions below. 

Common Causes

This is a list of common problmes that will trigger Audi check engine light to come on. 

• Oxygen Sensor - Reduced power and increased fuel consumption.
• Worn spark plugs - Reduced power, increased fuel consumption and in some cases even engine shaking due to a misfire.
• Ignition Coils / Coilpacks - Unburned fuel, engine shaking, catalytic converter glowing red.
• Vacuum leaks - Unstable idle RPMs due to Intake Air System Leak from cracked and loose hoses.
• Bad catalytic converter A fault code pointing to Catalyst Efficiency Below Threshold. Difficulty accelerating especially uphill.
• Low-quality gas - Check engine light on and reduced power.
• Turbo Problem - Reduced power
• Ignition Control Module - Will typically trigger multiple cylinder misfire codes.

How to Diagnose Audi Check Engine Light

Follow these steps to read the check engine light on any that's the model year 1996 or newer.

For this procedure, you can use a generic OBD-II scanner but an Audi OBD-II scanner that will read Audi manufacturer codes is recommended. 

1. Locate the OBD-2 port under the dashboard on the driver's side. 
2. Plugin your OBD-2 Scanner into the OBD2 port.  
3. Turn key to position II. All the dashboard lights will turn on. Do not start the vehicle. If your Audi has a Start/Stop button you will need to press the Start button without pressing the brake pedal.  
4. Allow the OBD2 scanner to turn on and connect to your Audi Engine Control Unit (ECU).
5. Read / Clear Audi Codes. Read Audi check engine light codes from the Engine Control Unit (ECU). Follow the same procedure to clear the fault codes by going to the Erase Faults (DTC) menu option. 

We don't recommend clearing Audi check engine light without fixing the problem.

First, you need to read the codes. Figure out why the CEL turned on and fix the problem.

Once you find what caused your Audi check engine light to come on and fix the problem, you can use the OBD-II scanner to clear the code. As long as no other codes are present. 

These instructions work on all 1996 and newer Audi vehicles including A1 A3 A4 A5 A6 A7 Q3 Q5 Q7 TT models.

Audi check engine light is flashing

If your Audi check engine light is flashing it indicates that there is an engine misfire which means fuel is not getting burned in the cylinders.

Engine shaking is often caused by a worn spark plug, bad ignition coil, Ignition Control Module (ICM), or bad catalytic converter.

FAQ

• Should I clear the check engine light without fixing the problem?  
  • Clearing Audi check engine light without fixing the issue does not solve the problem. In fact, if you fix the problem that caused your Audi check engine light to come on but didn't clear the light, the CEL will reset on its own typically within 5 or 6 driving cycles.
• Do I have to use a scanner to reset the Audi check engine light, if the problem is fixed? 
  • You don't need to use a scanner to reset the Audi check engine light as long as the problem was resolved. Within two to three days of normal driving, the check engine light will reset itself (CEL will turn off).
• Can I drive with the check engine light on? 
  • Yes as long as the check engine light is not flashing. If after a few days the CEL remains on you will need to read the codes. Don't ignore Audi check engine light even if the car drives fine. 
• Can a Loose Gas Cap Turn on Audi Check Engine light?
  • Yes
• Why is my Audi check engine light on? 
  • To find out why your Audi check engine light is on, you or your mechanic can use an OBD-II scanner to read the fault codes via the diagnostic port under the dashboard.