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Old 12-23-2018, 01:39 PM   #1
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Default Chevy Dashboard Battery Light Came On!

I've got a 2004 Chevy Express based Roadtrek. Last night, on a 5 hour trip south, we stopped for gas halfway and upon getting back on the highway I saw the little red light on the dash for my battery, I also noted my battery was at 11 volts! I planned on exiting the asap but the light went off and the readout was at 13.9 volts. It stayed off the rest of the trip and mostly at 14 volts. It was cold and I had the heater fan blowing full blast most of the time. When I reached my destination I noted that with the engine off the battery was reading 12.4 volts. Has anyone had this happen to them? The battery is a cheapo Walmart I've already replaced once. I suspect it is the problem.
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Old 12-23-2018, 02:10 PM   #2
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I've got a 2004 Chevy Express based Roadtrek. Last night, on a 5 hour trip south, we stopped for gas halfway and upon getting back on the highway I saw the little red light on the dash for my battery, I also noted my battery was at 11 volts! I planned on exiting the asap but the light went off and the readout was at 13.9 volts. It stayed off the rest of the trip and mostly at 14 volts. It was cold and I had the heater fan blowing full blast most of the time. When I reached my destination I noted that with the engine off the battery was reading 12.4 volts. Has anyone had this happen to them? The battery is a cheapo Walmart I've already replaced once. I suspect it is the problem.
Last year I installed a battery cutoff switch which was behind the battery such that you kind of just forgot it was there. It went bad over a short period of time and resulted in odd voltages. Mine chassis is also a 2004.
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Old 12-23-2018, 10:23 PM   #3
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Sounds like you may have a loose wire on your alternator and not making contact. I would check for loose wires on the alternator and on the battery. It could also be a bad ground wire that jars loose or is loose and drawing a lot of current running the heater on high.
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Old 12-23-2018, 10:35 PM   #4
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Sounds like you may have a loose wire on your alternator and not making contact. I would check for loose wires on the alternator and on the battery. It could also be a bad ground wire that jars loose or is loose and drawing a lot of current running the heater on high.

You might have an battery isolator that is failing intermittently. When the low voltage is present, you would just need to check the input to the isolator and see if it is the same as the low voltage at the battery. They should close to the same, with the battery being about .7v lower.
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Old 12-24-2018, 01:03 PM   #5
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You might have an battery isolator that is failing intermittently. When the low voltage is present, you would just need to check the input to the isolator and see if it is the same as the low voltage at the battery. They should close to the same, with the battery being about .7v lower.
in this case, would bypassing the isolator allow me to continue driving?

BTW do you know if the alternator is the 145 version in this Roadtrek of mine (2004 Chvey)?

Thanks!
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Old 12-24-2018, 01:19 PM   #6
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in this case, would bypassing the isolator allow me to continue driving?

BTW do you know if the alternator is the 145 version in this Roadtrek of mine (2004 Chvey)?

Thanks!

Yes, bypassing the isolator would get you going if it is the problem.


AFAIK, all the Chevy Roadtreks of the 2003 and up vintage used the 145 amp alternator.
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Old 12-24-2018, 09:20 PM   #7
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in looking at the isolator, it is not clear to me how i bypass it

is there a diagram somewhere online?
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Old 12-24-2018, 09:46 PM   #8
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in looking at the isolator, it is not clear to me how i bypass it

is there a diagram somewhere online?

Hopefully, some others are familiar with that particular isolator to know the connection locations. The goal is to get the cable from the alternator connected to the cable to the starting battery. You likely can just move the alternator cable to the same stud as the starting battery is on.
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Old 12-25-2018, 03:54 PM   #9
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so now the question is where do I get a replacement isolator? and given Roadtrek has switched to separators, should I get one of those instead? Would I be able to use a separator with existing wiring? TIA & Merry Holidays!
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Old 12-26-2018, 03:42 AM   #10
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Default Isolator bypass

Bypassing the isolator is relatively simple. You need to disconnect both batteries first! With the batteries disconnected, note the 3 large terminal studs on the front of the box. Using a 7/16 inch box wrench (or an adjustable) remove the wires from the outer terminals and put them on the center terminal. In other words, all 3 large wires are on the center terminal. Everything will operate normally with one caveat: since there is no longer isolation between the 2 batteries, you must be careful when boondocking to not run the batteries down to the point where you no longer have power to start the engine.

Replacement isolators are readily available at marine stores, RV stores or over the Internet. You will need an amperage model equal to or greater than your alternator rating. On Chevrolet chassis it is 145 amps. I am not sure regarding other manufacturers chassis but it will be similar. You can also convert to a separator relay.
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Old 12-26-2018, 01:35 PM   #11
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So I did bypass the isolator but the way I did it I just moved the wire from the alternator to the post for my starter battery. I like the alternate idea of putting the connectors all on the center post thereby allowing me to charge the house batteries while driving. I am not concerned with running down the chassis battery while boondocking as this will be a short term work-around as I will likely stay at sites with hook-ups. Plus I have solar and my generator and my emergency battery start pack. Thanks for the advice!
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Old 12-28-2018, 06:19 PM   #12
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You might have an battery isolator that is failing intermittently. When the low voltage is present, you would just need to check the input to the isolator and see if it is the same as the low voltage at the battery. They should close to the same, with the battery being about .7v lower.
You nailed it Booster! Thanks again!
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Old 12-30-2018, 09:47 PM   #13
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Another potential problem that shows up with the same symptoms that you discussed is a bad connection in the small gauge wire from the battery isolator to the alternator. This wire provides current to "excite" the alternator and get it putting out current. Sometimes a weak connection will become OK as the engine vibrates sometime after start-up. The weak connection could be right at the small post on the isolator, at the crimp where the connector to that post is attached to the wire going to the alternator, anywhere along the wire or at where the wire connects to the alternator. If the battery light stays on again after the engine has been running for a minute try working the small wire coming out of the isolator, this could re-establish a weak contact and suggest a solution without replacing the isolator.
BJ Chevy RT 190 Pops Fl Keys
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Old 12-31-2018, 04:06 AM   #14
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in looking at the isolator, it is not clear to me how i bypass it

is there a diagram somewhere online?
Hey, your picture shows rusty terminal connections. They should be bright and clean. I suggest disconnecting all cables and wire brushing all connections before reassembling. That may not be the problem but would be a good place to start.

My experience is based on old rusty cars while living near NYC. DougB
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Old 12-31-2018, 03:20 PM   #15
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Another potential problem that shows up with the same symptoms that you discussed is a bad connection in the small gauge wire from the battery isolator to the alternator. This wire provides current to "excite" the alternator and get it putting out current. Sometimes a weak connection will become OK as the engine vibrates sometime after start-up. The weak connection could be right at the small post on the isolator, at the crimp where the connector to that post is attached to the wire going to the alternator, anywhere along the wire or at where the wire connects to the alternator. If the battery light stays on again after the engine has been running for a minute try working the small wire coming out of the isolator, this could re-establish a weak contact and suggest a solution without replacing the isolator.
Good points! Thanks very much. However, I have decided to install a separator in place of the isolator. I do wonder: what am I supposed to do with that little sensing wire from the alternator...?
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