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the ABS light saga continues...


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As you may remember from past posts, over the last few weeks I have had my amber ABS light on the dash interminantly coming on and going off while I drive my caddy. It's very interminant, and can go days without coming on, when it does come on, it never satys on for more than a minute, then goes back off. The weird thing is when it happends to come on WHILE i'm breaking I can feel the ABS kicking in (Pulsating feeling in break petal).

I checked for codes, there are none.

Here's the breakthrough I have discovered though:

I have, in my trunk, 2 "10 subwoofers in a sealed box, driven my a 400 watt audiobahn amp. When I installed this addition to my audio system I also installed a kill switch under my dash, so I could just listen to the regular 4 speakers inside my caddy if I so desired.

When the ABS light does deside to flicker it ONLY happens when my amp is ON. It also only happend when the volume is turned up past a certain level, but it is still very intermittant. I drove around for about three days straight, absolutly blasting my subs with songs with the most bass I could find and no ABS light, then all of the sudden, it starts back up again. When it is on the light sometimes pulses with the music.

now keep in mind i'd had this audio system in place for about 2 months before this started happeneing.

I've done some research in my eldorado manual and it said is the computer for the ABS sensed low voltage the light would come on until the voltage comes back up....but why would this cause the ABS brakes to actually engange, and why would it only happen sometimes???

So I'm thinking it's either low voltage caused by the draw of my amp, or something is wiggling loose due to the vibrations from the sound. Someone also suggested the vibrations could trick a sensor into engaging the ABS. It's so confusing though, cause it only happens sometimes. But at least I know this, it NEVER NEVER happens without my amp on.

what do ya'll think!


Crystal Red Tintcoat Exterior | Shale/Brownstone Interior | 32k

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I seem to remember reading in the service manual that due to the various computers and their voltage sensitive nature, they recommended NOT adding any aftermarket electronics. I suspect that you have found a power source for your amp that also supplies your ABS computer, either directly or indirectly. If so, the wiring probably does not have enough ampacity to supply the amp and the ABS.

What I would do is route a new power wire directly from the battery thru a seperate on/off switch to your amp. This will keep the other circuts free from excessive voltage draw and any electronic interference generated by the amp. Be sure to use an adequate size of wire to carry the load. Check with the amp's manufacturer for the wire size that they recommend.

(Always use good brand name componets. Even with good wire, a cheap switch can cause problems.)

If your alternator and battery are in good shape it should eliminate your brakes trying to keep time to the music. ;)

That leads to the other thing. --- You stated that the amp has been installed for a couple of months and didn't cause a problem until lately. I would check out three things in the following order:

1. Check the battery cables for thghtness and cleanliness. Loose and/or dirty connections can cause a lot of wierd problems in these cars.

2. Check your battery. If it is loosing a cell it can cause problelms as well.

3. Check your alternator output. If your car's DIC will display voltage, select voltage and make notes on what it is at various speeds with the amp on and again with it off. If your voltage is falling below 13.2 or so, you may have an alternator issue. Also check the voltage before starting the car, after it has sat overnight. If the voltage is below 12.8 or so, it indicates that either there is a draw on your electrical system or the battery it's self is going bad. A lot of places like AutoZone can check your battery and charging system for free.

Something has changed since the amp installation, most likely the battery or it's connections.

If infact, you do find bad connections, I would still change the power source to your amp. These cars computers are voltage sensitive and you could cause one or more of them to fail due to the low voltage issue. :(

Good Luck,


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thanks for the tips!

I do have the amp running on it's own power wire directly to the batter as per the manufacturer's intructions.... 8 guage wire I believe, with its own kill switch and it's own fuse, nothing else runs on this power wire I installed except the amp - it is completely on it's own personal circuit

I have installed a good bit of car sound systems in my life and have a general knowledge of electronics, ect....I am a computer tech for a living, however you did not know this, so I understand your concerns and thank you.

I have been watching the voltage as well, while driving down the road it hold 13.8 or so, flip on the amp and no change what so ever, even with songs with alot of "thump" it holds at 13.8 volts. The batter is about 6 months old.

thats all for now....the investigation continues...

-dave B)

Crystal Red Tintcoat Exterior | Shale/Brownstone Interior | 32k

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