Why is my Audi Check Engine Light On?

Audi Check Engine Light ON A1 A3 A4 A5 A6 A7 Q3 Q5 Q7 TT

In this guide, you will learn about common problems that trigger Check Engine Light (CEL) and Service Engine Soon (SES) light to come on and how to retrieve the codes yourself using an OBD-II scanner.

If your Audi check engine light turns on a fault code (Diagnostic Trouble Code / DTC) gets stored in the Engine Control Unit (ECU). 

Retrieving Audi check engine codes is so simple that you can perform in your driveway. You need an OBD-II scanner some of which cost as little as $15. 


audi check engine light

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

  • Check engine light warning light on a dashboard
  • Poor fuel economy
  • Reduced power
  • Engine shaking¬†
  • Transmission not changing gears

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.

Common Causes

The cause of Audi check engine light can be something as simple as a loose gas cap to a sign that a serious engine or transmission problem is underway.

Loose Gas Cap


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.

You don't need to use a scanner to reset 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).

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.

Follow the instructions below to learn how to read and clear Audi fault codes.

Additional problems that often trigger Audi check engine light. 

  • Oxygen Sensor - Reduced power and increased fuel consumption.¬†
  • Worn spark plugs - Reduced power, increased fuel consumptions 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

Reading Audi check engine light is very simple. These instructions work on 1996 and newer Audi vehicles including A1 A3 A4 A5 A6 A7 Q3 Q5 Q7 TT models.

What you will need

What's the best scanner? 

Scanners that are designed specifically for Audi such as Audi VAG COM Scan Tool will provide accurate problem descriptions. 

Don't have a scanner?  

Some auto parts stores (Autozone, Advance Auto Parts) and auto repair shops will read your check engine light codes free of charge. 


To read Audi check engine light as outlined in this guide, you will need an OBD-II Scanner.

Find OBD-II Port

Locate OBD-2 port under the dashboard on the driver's side. This is a 16-pin port. All 1996 and newer Audi vehicles have this port.

Connect the scanner to OBD-II port

Plug in your OBD-2 Scanner into the OBD2 port.

Audi Check Engine Light ON Troulbeshooting


Turn on ignition

Turn key to position II. All the dashboard lights will turn on. Do not start the vehicle.

How to diagnose Audi check engine light service engine soon A1 A3 A4 A5 A6 A7 Q3 Q5 Q7 TT

If your Audi has a Start/Stop button you will need to press the Start button without pressing the brake pedal.

turn audi on to read codes check engine light related

Turn on scanner

Allow the OBD2 scanner to turn on and connect to your Audi Engine Control Unit (ECU).

Check Engine Light On Audi


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 Erase Faults (DTC) menu option.


Don't clear Audi check engine light without fixing the problem. You need to figure out why the CEL turned on. Once you find what caused CEL to come on, fix the problem.

Often we see people disconnect the battery or use a scanner to clear Audi check engine light.

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.

Why is my Audi check engine light is flashing?

audi check engine light on due to bad spark plug ignition coil pack A1 A3 A4 A5 A6 A7 Q3 Q5 Q7 TT

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.

It is not recommended to drive an Audi if the engine light is flashing. Operating an Audi for an extended time when the check engine light is flashing will cause damage to the catalytic converter.

It is better to have the car towed to prevent further engine problems. If your Audi CEL light is flashing, it indicates that the problem is more serious.

Under these conditions, the car may also go into limp mode (transmission not shifting gears).

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

Check Engine Repair Cost

The average cost to fix Audi check engine light can range from $150 to $500. It is difficult to determine the exact cost to fix Audi check engine light without pulling the codes first.

Auto parts stores such as Auto Zone or Advance Auto Parts may scan the codes for free. 

If you call an Audi mechanic they will ask you to bring the car in for a check-up which usually runs between $90 and $140.

We recommend you get an OBD-II scanner and retrieve the codes yourself. Even if you don't plan on fixing the problem yourself, you will have a better idea of what is wrong.

Once you retrieve the codes you can search for that particular code online, for example, searching for "Audi P0300" you will quickly learn that this code indicates multiple cylinder misfire.



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Erin T. made a comment.
1 year 1 month ago

I had the check engine light come on in my 2008 Audi A6. At firt I was warried as didnt' want to spend hundred on a repair. Got a $20 scanner on Amazon and read the codes. It turned out I had left my gas cap loose. Got a new gas cap and installed it anyway. Reset the light and it hasn't come on yet. I guess it would have turned off in a couple of days but at least I was able to figure this out on my own. I am grateful for your help.

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Alex Duncan made a comment.
3 weeks ago

I have a 2009 Audi a4 2.0 tdi s line. The engine light has been on now for about a year and its telling us it's the dpf area, 2 garages have checked and double checked and cannot find any fault with the car at all ?? Can anyone help!!??


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