Dash Lights Flicker When Car Is Off – 6 Reasons why


Flashing lights on the dashboard when the key is turned off can be alarming, but no need to panic. While it looks strange, it is a common issue. You’re in the right place, and in the following guide, we’ll cover everything you need to know.

The top 6 reasons dash lights flicker when the car is turned off, include:

  1. Faulty battery
  2. Looses/dirty battery cables
  3. Faulty ignition switch
  4. Faulty relay
  5. Loose dash panel block connectors
  6. Faulty dash control module

In this post, you’ll learn the most common causes of flickering dash lights. You’ll also learn how to diagnose them and how to fix them, by the end of this post you’ll be a pro.

Dash Panel Overview

Modern car dash

Your dash panel is more than just your Speedo and a collection of warning lights, it’s actually a computer (Control Module (CM)) tasked with managing various functions. Your car is packed with computer modules, each one tasked with a system to manage.

The PCM (Power-train Control Module) manages engine running, TCM (Transmission Control Module) manages the transmission, ABS module controls the brake system, Collision module manages airbags and belt tensioners, etc.

Although all these modules have clearly defined roles, they don’t operate independently. They communicate constantly with each other over a communication network known as CAN (Controller Area Network) and your dash panel is key to its operation

The dash control module, which is known by many different names and acronyms. Often referred to as DIM (Drivers Information Module), IP (Instrument Panel) DM (Dash Module) IC (Instrument cluster), etc.

Some modules are more equal than others though, your dash module is typically the gateway module on the communication network. Meaning, if your dash module goes offline, it takes out the whole system.

Your car’s security system is typically routed through the dash module. You’ll never look at your dash clocks in the same way.

CAN network info-graphic

1 Faulty Battery

Battery voltage is so important to modern computer-controlled cars. The computers as you know need to communicate with each other and they do so using high and low voltages. It’s Morse code for computers and so you can imagine what strange messages the modules are sending to each other.

Battery testing

The language becomes garbled and mixed up which can cause all sorts of seemingly strange things to happen. Some cars are fitted with a battery control module dedicated to managing power.

When it senses a power issue, the module overrides all other modules and shuts down many systems causing the car’s electrics to act funny.

Solving electrical issues should always begin with the battery. Let’s go ahead and test the battery making sure it’s up to the job. A battery typically lasts about 3-4 years Modern cars have large demands on power, check that your battery is the correct size for your vehicle.

Battery cranking test diagram

The following readings represent the state of charge of a battery at rest:

  • 12.7 – 13.2 volts is 100% charged
  • 12.4 volts is 75% charged
  • 12.2 volts is 50% charged
  • 12.0 volts is 25% charged
  • 0 – 11.9 volts is Discharged (Flat)

A battery could read a healthy 12.65 volts and still be faulty, so go ahead and run the crank test if the battery is at least 75% charged.

2 Loose/Dirty Battery Cables

Battery negative post

Loose battery cables are the number one cause of flickering dash lights and are the easiest to fix. Locate your battery, most cars store the battery under the hood, but if you don’t find it there. Expect to find it in the trunk, under the back seat, under the passenger seat underside of the car.

Inspect your battery terminals for corrosion. Battery acid sometimes leaks from the terminal posts, so you’ll need gloves and safety glasses, acid burns the skin. If you have a build-up of white crusty acid corrosion, neutralize it with some baking soda and water,

Now go ahead and clean, tighten and coat the terminals with some petroleum jelly, which helps prevent future corrosion. Your battery cables or terminals could be damage too so inspect them for breaks or bulges in the insulator.

A simple volt drop test is excellent for finding high resistance in battery cables, but you’ll need a voltmeter. You’ll find a voltmeter here on the Auto electrical repair tools page. Follow the infographic below.

Battery positive terminal volt drop test
Battery negative terminal volt drop test
Battery positive cable volt drop test
Battery negative cable volt drop test

High resistance in ground straps is a common cause of electrical gremlins. All vehicles will have a main ground strap from the battery to the chassis and the chassis to the engine. All other grounds on the vehicle depend on these main grounds. Common issues include loose straps; broken wiring; corroded wiring. Go ahead and check your straps, remove and clean if necessary.

Car chassis ground cables
Car ground strap
Ground strap

3 Worn Ignition Switch

The ignition switch initiates the whole process and typically sends power to the IP when ignition on the accessory (1) and also at ignition position 2. A worn-out ignition switch may cause the ignition to come on unexpectedly, broken internals could short the ignition circuit, powering it up.

Similarly a short in the circuit wiring could cause the ignition to power up, check for chafing of the ignition 1 and 2 power wires to IP.

Ignition switch info graphic

4 Faulty Relay

Starter Relay

A relay is designed with a load side and a control side. The circuits are independent and allow the control side circuit (typically low amp) to control the load side (high amp) without risking interior switches or sensitive circuits.

Your IP may or may not be controlled by a relay. Check your fuse box for a listing. While at the fuse box check the main fuse contact points are clean by removing and inserting a few times.

If you have a relay, remove and check the pins for corrosion, damage, water, etc. To test the relay, give it a shake and listen for a loose armature. Very often your fuse box will contain many identical relays. Try swapping out the relay for a similar relay, but be sure the pins match.

Follow the info-graphic below to hotwire the relay (once removed) and check for continuity.

Check out the Auto electrical repair tools page where you can see many of the tools I use.

Relay testing

5 Loose Dash Clock Connectors

The dash module isn’t easy to access and higher-end cars may require special tools to access. Don’t be surprised if other components like the airbag and steering wheel need to be removed.  Loose block connectors at the rear of the dashboard are common on cars without modern cam-lock block connectors.

After you gain access, don’t remove the block connectors, instead wiggle the wiring and block connectors systematically and check for a change of the condition.

Dash clock graphic

Remove the connectors and check for corrosion, damage, moisture, bent pins on the clock side. Check for pin tension on the loom side. Poor tension is a common cause of intermittent problems, a drag test will reveal any issues. Coat the pins with a thin coat of dielectric grease.

6 Faulty Dash Module

VW steering wheel

Dash modules are complex bits of kit and we won’t even try to understand how it works. But that doesn’t mean we can’t test it or fix it.  We can check power inputs, grounds and check for chaffing of wiring on the power side.

Your module will have an ignition 1 and 2 and also a power feed for the logic circuit. It’s important to check the ground also. Perform a volt drop test to identify high resistance.

IP info-graphic

We can remove the clock, open it and check for obvious visual signs of damage such as water or damaged circuits. Broken solder or corrosion on the circuit boards is common, these types of issues can usually be repaired easily with a little solder and some patients.

Related Questions

Dash lights not working fuses good? The dash lights dimmer switch is often accidentally turned to full dim, locate your dimmer switch and try adjusting it.

John Cunningham

John Cunningham is an Automotive Technician and writer on Rustyautos.com. I've been a mechanic for over twenty-five years, and I've worked for GM, Volvo, Volkswagen, Landrover, and Jaguar dealerships. My passion is cars. I use my knowledge and experience to write articles that help fellow gear-heads with all aspects of car ownership, including buying advice, maintenance, and troubleshooting.

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