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Car Amp Turns On But No Sound From Subs

Car audio systems can be quite complex, and their problems are often difficult to root out (been there … done that). This is especially true for inexperienced car audio enthusiasts.

In addition to having all the same components of home audio systems, car audio systems live in unforgiving environment and are subjected to temperature extremes, vibrations, rumbles, and other stresses on the road.

So while car audio amplifiers are just one component among many, the problems they can introduce should not be underestimated.

Having an amp that turns on but no sound from subs is one of the most common problems that you’re likely to encounter if your car audio system is powered by an external amplifier. This is different from an amplifier that is in protection mode but it is related.

We have come across a ton of people who had to deal with this problem, at least once. We do understand how frustrating it is. And for this reason, we’ve put together these quick and easy steps that you can run through to diagnose and fix the problem.

Six Quick Checks

Lots of car audio systems will experience no sound from the subs even though the amplifier seems to have power, and there are all kinds of causes.

Some of this can be caused by a broken amp (which you can easily figure out), but all of them can be caused by other underlying issues that will still be around even if you try to fix the problem by replacing your amp with a new one.

If your subwoofer suddenly stopped working but the amp is on, or if you believe you have everything connected properly, but your subs don’t seem to make any sound at all, the following steps should help you track down the problem.

It goes without saying that a car audio amplifier needs several things in order to work perfectly, and we’ll check each of these below.

1. Check if your amp is mounted to a non-conductive surface

The very first thing you need to do is to make sure that your amplifier is mounted to a solid, non-conductive surface (non-metal) of the vehicle. A car amplifier that’s in contact with bare metal can cause all sorts of problems. Typical symptoms of this include switching into protect mode, clipping, or not turning at all …etc.

2. Check the subwoofer settings in your receiver

Most – if not all – aftermarket car stereos have a separate subwoofer control in the settings. If it’s turned off or set really low, your subs won’t be able to produce any sound when the amp is on. Therefore, check your settings and make sure the subwoofer output is turned on and that the dB levels are set more than 0.

3. Check your amp’s power and ground connections

It goes without saying that an amplifier requires both a positive power input and a negative power output. The power to the amplifier must be able to get in and get out in order for anything to happen.

That said, you need to make sure you’ve got adequate power at your amplifier. Some amps can turn on with 6 – 10 volts, but most of the time that is not in the operating voltage range for the amp to actually function. So, use a voltmeter to check the voltage between the positive and negative terminals of the amplifier. It should read about 12 volts with the engine off and around 14 volts with the engine running.

If the amplifier is not receiving power, you’ll need to check the connections for both the power wire and the ground wire at any point they could come loose (grounding bolt, distribution/fuse block, outboard fuse holder, battery connection, etc.).

The amplifier uses the power it receives to boost the inaudible line-level signal from your head unit so it’s powerful enough to move a speaker’s cone back and forth to create sound.

If the wiring is not correct, or too small for the amplifier, or if a connection is loose you’ll get no output.

Additionally, if your amplifier has a built in fuse, you’ll need to check that it’s not blown. Do not rely on a visual inspection but instead switch the amp off and remove the fuse and test its continuity with a multi-meter. It should read something close to zero ohms.

4. Check if the amplifier is receiving a turn on signal

The remote turn on wire is a blue wire (typically with a white stripe) that’s responsible for turning your amplifier on and off. If it isn’t installed correctly, your amp will not turn on even if it has good power and ground connections OR it may constantly draw power and drain your battery over night.

The turn on wire signal is provided by the head unit when the ignition is on. This signal is transferred through the remote turn on wire to the amplifier turn on circuit; when the amplifier senses this voltage, it turns the amplifier on.

Some head units come with two blue leads. One to turn on the amplifier and other processors (active crossovers, car audio equalizers, etc.) while the second lead is dedicated to the power antenna. The latter will only be active when the radio is on. It will not have power when another source such as CD or Aux is selected.

One thing to note, in older vehicles, wiring remote turn on to power antenna was a very common practice and worked just fine because when the radio was on, the power antenna was up and working. However, in most modern vehicles we’ve come across, the power antenna may only be receiving power when the headunit is in AM/FM mode. If you switch to Auxiliary input, CD player, satellite radio, SD card, etc… the power antenna wire will stop receiving power and your amplifier will not turn on.

So, if your amplifier only works with the radio you may have the power antenna lead connected to the amplifier instead of the remote lead.

With all of that being said, check this connection by turning on your head unit to a source other than radio, and use a voltmeter to check the voltage between the remote turn on terminal on your amp and the ground. It should be around 12 volts. If it isn’t change the headunit to the radio and see if it has voltage. If it does, you probably have only the power antenna lead connected instead of the remote turn on lead.

In case there’s no voltage whether the radio or other source is chosen, then it’s highly likely that there’s something wrong with your remote turn on wire.

Again, check the connections for a second time and if they are tight and secure, you’ll need to pull the receiver out of the dash to access this lead and check its voltage.

There should be a small fuse in that lead that may have burned out. Or if there is no fuse the circuit itself may have burned out. If that’s the case, you’ll probably need to buy a new receiver.

P.S: A temporary workaround is to use a small jumper wire between the positive terminal of the amplifier and the remote turn on terminal. This will allow you to carry on with the next tests, however, this workaround must be removed after the tests, otherwise the amplifier will remain on at all times.


5. Check if the amplifier is receiving a music input signal

It goes without saying that in order to get music out you have to have music in. Music signal is provided to the amplifier through speaker level inputs (also known as high-level inputs – not all amps have these,), or through low-level inputs (also known as RCA inputs or low-level inputs)

Almost all modern aftermarket headunits these days have at least one pair of RCA outputs. Some have up to three pairs of outputs (front, rear, subwoofer). However, factory receivers will only have speaker outputs which can be connected to high level inputs or converted to low level (RCA) outputs using a line output converter.

Now, if your subwoofer is not working but the amp has power, then you’ll want to make sure the amp is receiving an input from your head unit. This is a pretty easy process as you’ll simply need to unplug the RCA cables from each unit and reconnect them with a good set.

Make sure the head unit is turned on, and that the volume is turned up. If everything works after bypassing the installed RCA cables, then you’ll just need to replace them with a good set. If you get sound from one input but not another, the problem is in your head unit, and not your amp.

If these connections (either low or high) are properly connected and the wires are in good shape but you still don’t get any output from your amplifier, you’ll need to check the gain on your amp. The latter is what matches the output signal of the head unit to the input section of the amplifier.

So, with the head unit on and the volume at about half, adjust the gain control on your amp and see if any sound is produced. If you’re hearing your music through the speakers or subs, keep adjusting your amp’s gain until the music sounds clean.

If you still don’t get any sound, and in order to tell if it’s because of lack of signal, use a portable music player (CD or MP3) with a 3.5mm to RCA adapter cable and plug it into the amplifier’s input. If your subs start to produce sound then you know it is a problem with the input signal.

This means two thing to us: Either there’s a poor connection or that another unit upstream such as a crossover is what’s stopping the signal between the head unit and the amplifier.

If any component between the head unit and the amplifier is stopping the signal then it needs to be checked out as well. To carry on the troubleshooting process, try bypassing that unit/component by isolating it and run the signal directly from the head unit to the amplifier.

6. Check if the amplifier is outputting a signal

Now that we know that the amplifier is getting signal, and it’s turning on, it’s time to check the speakers outputs.

To check if your amp is outputting a signal, you’ll want to disconnect it from the speakers in your vehicle and then pick a good test speaker and hook it up to one channel of the amplifier at a time.

If the amplifier drives that just fine on all channels then you know something is wrong downstream (after the amplifier). This could be faulty speakers, problems with the speaker wiring or simply a bad connection.

If the amp turns on but there is no output to the test speaker, then it’s highly likely that you have a faulty amplifier, although you’ll want to check that it isn’t in “subordinate” mode and that you don’t have conflicting filters before you condemn the unit.

Bottom Line

So, that’s all there is to fixing a car amplifier that seems to be working just fine, but you still don’t get any sound from the subs. Most often it’s a simple and easy fix that you can sort out at home yourself if you have some spare time rather than going to your local car audio store to save you some bucks.

If you couldn’t figure out what’s wrong with your car audio system — or want to pick my brain on anything in the article — leave a comment below. We would love to see how We can help out.

Alex Brown

Hey There, my name is Alex Brown, I'm an LA-based sound engineer with over 10 years experience installing, troubleshooting, and repairing commercial, automotive, and household sound equipment. I've installed highly competitive car audio systems, and everything from navigation systems to full car stereo systems, remote starters, alarms and beyond. I enjoy creating solutions and simplifying everyday needs. I also love helping people get great sounding gear, thereby, saving the world from bad sound one customer at a time.

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