Car radios are an integral component of the driving experience, providing entertainment and information to drivers and passengers.
However, sometimes their functionality only extends as far as accessory mode will allow – disallowing drivers from accessing it during actual vehicle operation.
In other words, some vehicles may develop an issue where the radio only works in accessory mode (ACC mode) and shuts off when the vehicle starts (i.e. when the engine is engaged).
There could be any number of reasons for why a car radio only functions in accessory mode; from straightforward fixes to complex electrical issues. Common causes include faulty ignition switches, blown fuses, wiring or connection problems.
In this article, we will explore why your radio may only work in accessory mode, potential solutions to address these issues as well as suggestions on how to identify and remedy such problems.
We will also explore effective methods of avoiding future complications.
What Is Accessory Mode?
Accessory mode in cars allows certain electrical features like radio, power windows and headlights to function without the engine providing power.
Instead, battery power is used, allowing drivers to listen to music or use other electrical features while the vehicle is parked and the engine is off without risk of engine malfunction.
It allows motorists to enjoy music or using other electrical features when necessary while their engine remains off.
To enable accessory mode, generally speaking you will need to turn your key over one click closer than off to “accessory” (i.e turn they key to the ACC position), with some newer vehicles offering push-button ignition systems with an “accessory” button for this purpose.
With some vehicles, this mode requires that you press the button with one quick press.
Notably, using accessory mode for extended periods may drain a car’s battery, so only use it briefly and strictly according to manufacturer restrictions so as to keep it from draining too rapidly.
Furthermore, certain vehicles have limits as to which electrical systems can use accessory mode in order to preserve battery power and avoid it draining too fast.
Why Does My Car Radio Only Work In Accessory Mode?
Your car radio may only function in accessory mode due to various reasons; here we explore some of them.
We also present solutions to fixing the issue of a car radio only working in accessory mode since the solution depends on the underlying cause of the problem.
1. Ignition Switch
A common reason that car radios only function properly in accessory mode is a malfunctioning ignition switch.
The ignition switch supplies power to all electrical systems within your car – including radio and stereo components.
When malfunctioning, however, power may no longer reach them when driving but may still provide power when accessory mode is activated.
If the ignition switch in your car has become malfunctioning and no longer supplies power to the radio when driving, a mechanic should assess and replace if necessary.
They can diagnose the cause before replacing any necessary switches.
It could also be possible that the reason your car radio only functions in accessory mode is due to wiring problems.
There may be something amiss between its connection with your vehicle’s electrical system and where your radio plugs in, and power being delivered during run mode.
In such instances, the accessory mode could still provide enough juice so the radio would work – although only during car operation mode itself.
If there is an issue with the wiring that connects the radio to the car’s electrical system, repairs or replacement may need to be performed on it.
A qualified mechanic should conduct an evaluation to ascertain which path would provide optimal solutions.
If you are technically able and want to make some checks yourself and verify that there are two power feeds connected to the head unit.
Firstly, you need to check if you have a bad ignition wire going to your stereo harness. This is a common problem.
You should have one power feed from the ignition ACC (red wire in head unit wire harness) and another power feed via an inline fuse (yellow wire in head unit wire harness). Both of these should be connected to the battery.
Here is the breakdown:
ACC Wire – Power comes from the battery, through a fuse (about 30A), to the ignition switch, and then from the switch to a fuse (about 10A), to the radio.
Constant 12 – Power comes from the battery or alternator through a fuse (about 75A), to another fuse, and finally to the radio.
You will also see as a standard, one black ground, one blue remote amp (unused if there is no amplifier in the car), and 4 or 8 speaker wires.
Use a multimeter and check if power is being supplied to the appropriate connections on the radio. Once power is supplied, the radio should work unless the accessories relay is flicking when the engine is started. You can start the car while the head unit is opened, exposing the relay so that you can check if this is the case.
You can follow the procedure below (note that the wire colors and pins may vary depending on your vehicle make and model, so consult your schematics):
- Get a multimeter, and check for constant power at pin M (the +12V battery wire – the color of the wire will depend on the car make and model, but it is normally pink or yellow). This should be a constant 12 V, however, 11-14 volts should always be here.
- Check pin G (the +12V ignition wire – the color of the wire will depend on the car make and model, but it is normally blue or red) you should have no voltage.
- Turn the switch to ACC and 12VDC should be there
- Then start the car and 12VDC should still be there
- Check ground from the chassis
Your car battery provides power to all its electrical systems, including your radio.
If the battery is old or weak enough, it may no longer provide sufficient power during vehicle operation; although accessory mode could still supply enough power allowing your radio to function.
In such circumstances, the radio will only work in accessory mode.
If your car battery has become old or weak and no longer provides sufficient power for radio playback while driving, a mechanic may suggest having it tested to see whether a replacement is needed.
He or she can then conduct these services themselves should their advice prove necessary.
If you want to test the battery yourself, consider the following procedure:
Some cars may show you a battery notification on the dashboard, produce weak headlights, or only slowly crank when you start it.
These are often good indications as to the health of your battery. However, for a more accurate way to figure out if your car battery is causing your radio malfunction, follow the steps below.
- Set your multimeter to about 15VDC.
- Switch on your headlights for about two minutes.
- Connect the positive lead and negative leads of the multimeter to their respective terminals on the battery (black to negative and red to positive).
- You should see a result of at least 12.6 volts.
- Keep the multimeter attached to your car’s battery.
- Turn on the Ignition.
- The result should not drop below 10 volts.
- If the reading falls below 10V, you need to clean your battery or replace it if a technician reports that it should be replaced.
If you prefer watching video tutorials, visit Chris Fix’s clear and detailed clip about testing a car battery with a multimeter:
If the radio stops getting power when running the car but works when in accessory mode only, there may be an issue with its fuse.
A fuse protects all electrical systems within your car from power surges or any other issues.
When damaged, it could prevent power from being supplied when needed but may still function normally during accessory mode use.
If the radio stops functioning when driving because of a blown fuse, replacing it could be necessary.
A mechanic can locate your fuse box and replace any that are broken; just as importantly they could also locate any that have gone bad before that may need changing as soon as possible.
5. Outdated Software
Newer cars are manufactured with radios that require software to operate. For any number of reasons, such software may begin to malfunction.
One possible result is that the radio may only work in accessory mode. This is not a very common reason for this problem, but it is worth looking at just in case.
If your radio requires software updates in order to operate optimally and perform as intended, please make sure that you update it.
Some auto manufacturers provide updates specifically tailored toward improving performance or fixing potential issues with existing software versions.
All you need to do is to follow the manufacturer’s instructions and update the radio software to the latest stable version.
Below are some common questions and related answers around the topic of car stereos and the accessory mode.
1. Does The Ignition Switch control The Radio?
Yes, the radio is directly controlled by the ignition switch. When the ignition switch is turned on, power is sent to the radio, allowing it to turn on as well.
The ignition switch also controls other electrical systems.
2. How Do You Know If Your Ignition Fuse Is Blown?
There are various ways to determine if your ignition fuse is blown. The easiest indication is if your vehicle does not start at all or stalls while you are driving.
To directly check the fuse, you can use a multimeter to check its continuity or simply visually inspect it to see if the filament is broken.
3. What Happens When You Turn The Ignition Switch To An Accessory?
When the ignition switch is turned to accessory mode, power is sent from the battery to the electrical systems that are designed to operate with the engine off.
Such systems include the radio, power windows and so on.
4. How Long Can I Leave My Car In Accessory Mode?
Keeping your car in accessory mode will use power from your battery if your battery is healthy. Typically, you can leave most cars in accessory mode for up to 30 minutes without draining the battery.
However, leaving the car in accessory mode too long will certainly drain your battery and your car will not start.
5. Why Does My Radio Have Power But Won’t Turn On?
If your radio has power but won’t turn on, there are several reasons that could be the cause. The most obvious and common ones are a blown fuse, a loose or disconnected wire, a faulty switch, or a problem with the radio’s internal components.
6. Why Does My Car Radio Turn On But No Sound?
If your radio has power but won’t turn on, there are several reasons that could be the cause. This is similar to when your car radio has power but won’t turn on.
Issues that may cause this problem include a blown fuse, a loose or disconnected wire, a faulty switch, or a problem with the radio’s internal components.
There can be several reasons why your car radio only functions in accessory mode, including an ignition switch glitch, blown fuse, or wiring issues.
Fixes to this problem range from simple DIY fixes like checking and replacing fuses to more involved solutions like rewiring its electrical system.
To determine an ideal solution, it is crucial that you accurately identify what the problem is before searching out potential fixes yourself or consulting professional mechanics or car audio specialists to prevent further damages or potential hazards from further occurring.
Norvan Martin is the founder of BoomSpeaker.com. He is a professional Electronics Engineer and is passionate about home theater systems and AV electronics. BoomSpeaker was created as an online hub to share his knowledge and experiences as it relates to home theaters and home audio electronics.