AudiWorld Forums

Audi A4 B8: How to Reset Check Engine Light

Let's hope that check engine light was a fluke, and make it disappear with the quick trick that anyone can do.

By Jacob Stumph - March 18, 2016

This article applies to the Audi A4 B8 (2009-2015).

That check engine light can be a pesky bugger. It's trying to help by alerting you of a potential problem, but without a code reader, you're speaking different languages. Fortunately, unless that CEL is flashing, it is usually safe to drive the car home. Once you've had the trouble code read (often for free) at your local auto parts store, and addressed with whatever needed repaired, the light may still be on. Here's the quick trick to resetting the evil light.

Materials Needed

  • 10mm socket and ratcheting wrench

A quick note for readers before we get cranking here: If you are looking to reset service lights, for things like engine oil and other general maintenance items, this is the end of the journey for you. In most instances, you are going to need VAGCOM to communicate with your Audi's maintenance minder and reset it.

(Related Thread: Reset Service Light After Oil Change - AudiWorld.com)

Step 1 - Locate your battery

Depending on your specific model of A4, your battery is in one of two places: tucked under the plastic cowling in the engine bay, or in the trunk of your car under the false floor. For models with the battery under the hood, the battery should be in the exposed, center portion of the cowl, and be readily available. For trunk-mounted batteries, all that is required is to lift up and remove the false floor in the trunk.

  • audi a3 a4 b7 b8 battery ECU CEL reset how to
    Figure 1. Cowl-mounted battery location.
  • audi a3 a4 b7 b8 battery ECU CEL reset how to
    Figure 2. Trunk-mounted battery location.

Step 2 - Remove negative terminal

Using your 10mm wrench, or ratchet, remove the negative (black) terminal from the battery. Wedge the terminal between the false floor, or otherwise secure it away from the battery. The goal is to keep the terminal from making contact. Wait approximately 15-20 minutes. In this time any residual charge in the car's electric system and ECU/DME will drain, resulting in a "hard reset" of the engine computer system.

audi a3 a4 b7 b8 battery ECU CEL reset how to
Figure 3. Audi has conveniently marked the terminals for positive (+) and negative (-).

Pro Tip

Be careful not to open any doors or tap any radio settings, etc., as you may lose any presets or one tap window function, and have to go through the relearning process for those as well.

Step 3 - Refit negative terminal and start car

After allowing ample time for the car's charging system to drain, refit the battery's negative terminal with your 10mm socket. From here, start the car up and check for trouble codes. The CEL should no longer be illuminated. Take the car for a test drive to check that your prior repair has worked and that the CEL stays off.

Related Discussions