Electrical malfunction/low voltage warning, intermittent

[Mike35r18]

I have a 2001 RD688S with an E7 400, and am having some electrical issues. There appear to be no signs or symtoms other than the low voltage alarm which may go off for quite a while, then for no explained reason, go off, then come back on again, or just start to rapidly start/stop as if there is a loose connection that is almost making contact after the truck has warmed up and gone for a short test drive. As I went to leave a parking lot after sitting, as I started pulling away the light started going on/off. Then the truck will occasionaly throw an electrical malfunction light, but since I started trying to diagnose this, I have not seen that light, not that I have a code reader for that truck anyways, nor even cruise control, so would there be a way to get that code without cruise? The dissapointing thing is it only has 1200 hours, 17K miles, and is always garaged. What could cause what I believe is a false low voltage alarm? Batteries are 3 years old, load tested well, alternator output is good, battery conditioner is working properly (always plugged in), so I am kind of at a loss at the moment, any ideas?

-Mike

[Rob]

I have a 2001 RD688S with an E7 400, and am having some electrical issues. There appear to be no signs or symtoms other than the low voltage alarm which may go off for quite a while, then for no explained reason, go off, then come back on again, or just start to rapidly start/stop as if there is a loose connection that is almost making contact after the truck has warmed up and gone for a short test drive. As I went to leave a parking lot after sitting, as I started pulling away the light started going on/off. Then the truck will occasionaly throw an electrical malfunction light, but since I started trying to diagnose this, I have not seen that light, not that I have a code reader for that truck anyways, nor even cruise control, so would there be a way to get that code without cruise? The dissapointing thing is it only has 1200 hours, 17K miles, and is always garaged. What could cause what I believe is a false low voltage alarm? Batteries are 3 years old, load tested well, alternator output is good, battery conditioner is working properly (always plugged in), so I am kind of at a loss at the moment, any ideas?

-Mike

Check via a load test for a shorted cell in one of the batteries first. If these test well, have the alternator checked via a load test. It could be an intermittent electrical connection point but from your description, I think the problem is more hardware related.

Rob

[Mike35r18]

Really? Ok, the batteries load tested well while still connected together, but should just isolate each of them (3 total) and test them seperately? What would the max allowable drop from a fully charged battery be? I had contemplated a bad cell (or a couple). Thanks for the fast response!

[slpwlker]

Yeah you need to Isolate them. You will never get an accurate reading otherwise. As far as drop I don't remember

[Rob]

Really? Ok, the batteries load tested well while still connected together, but should just isolate each of them (3 total) and test them seperately? What would the max allowable drop from a fully charged battery be? I had contemplated a bad cell (or a couple). Thanks for the fast response!

Check them individually. With a fully charged battery, take a voltage reading and record. I would then put a 500 ampere draw upon them for 30 seconds and take another voltage reading which should be at least 95% of the original reading. Look for a rapid fall off of current draw during the test; this is indicative of a bad cell.

Rob

[Mike35r18]

Excellent guys thank you, will try and report the findings, be back later.

[Mike35r18]

I learned something already, and that is my load tester is nowhere near capable of a 500 amp load, however I am looking to purchase one, 100-130 amp seem much more common, is 500 overkill for these batteries or is that the standard for that size? They are 950 CCA batteries, and the 500 amp testers I found test for 15 seconds, and are about $120.

[Rob]

Go to an automotive tool store and purchase what is called a "carbon pile". This is a real load tester for batteries and cheap ones will only be about $50.00. The little ones that are hand held will burn up if you run them very long as they dissapate the current and resulting heat through the cage. These are nothing more than a fixed resistance. Virtually worthless for checking batteries, (my opinion).

If you haul your batteries into an Interstate Battery Center, or Batteries Plus, either outfit will check your batteries for you with the hope of selling you new ones. They don't charge for this service but expect you to purchase theirs should your batteries be defective.

If you find a single battery with a bad cell, replace them all. They are in series connected in the truck. If you only replace the single battery that shows defective, the others will most likely take the new one out on short measure. Not saying get rid of them, just don't use them again in the same installation. For instance install the good pair into a vehicle that uses two batteries, or two different applications. Just don't use your know good, (but used) batteries with a new one in the same installation.

Rob

[Mike35r18]

Very good advice about replacing them all and using the other ones elsewhere, and yea the load tester is a carbon pile, and looks to be pretty nice, it is a K Tool International 500 Amp Carbon Pile load tester, should be all I need. And yes mine is a fixed resistance, and it is proving to be pretty worthless. While I have ya here, advice on a code reader for all my heavy trucks in case that malfunction light does come back? Found an OTC that also reads OBDII which I also need, but was really liking the Innova 3150 for that stuff.

[Rob]

Very good advice about replacing them all and using the other ones elsewhere, and yea the load tester is a carbon pile, and looks to be pretty nice, it is a K Tool International 500 Amp Carbon Pile load tester, should be all I need. And yes mine is a fixed resistance, and it is proving to be pretty worthless. While I have ya here, advice on a code reader for all my heavy trucks in case that malfunction light does come back? Found an OTC that also reads OBDII which I also need, but was really liking the Innova 3150 for that stuff.

I have the Innova you mention as it does the new CAN standard also but is backward compatible with OBD-II which is becomming obsolete. OTC stuff is pretty good and upgradeable, but simply too expensive if not used often. I typically look to purchase this type of stuff second hand as I'm not working on new vehicles daily.

Rob

[Mike35r18]

Ok well, the alarm is still intermittant, I picked up an OTC professional electrical system tester that is supposed to be able to detect bad voltage regulators, battery cells, etc, it says that the batteries are all good, yet one tested at 750CCA, then 850CCA, when they are 950 CCA batteries. There are 3 batteries, that being the worst. One was about 900, the other 930. So after not finding anything several times, including isolating and testing each battery, I put the tester directly on the alternator which detected "excessive ripple", obviously pointing to a bad alternator, but since I put the charger there is that accurate, or have I messed up the test by placing it so close to the voltage source? I replaced the regulator on the alternator about 4 years ago, was thinking maybe this was a bad connection on a low voltage alarm, which Idk where that is mounted, but am leaning more toward alternator and batteries now, since also finding them low on water last week. Filled them, drove the truck and retested, still throwing the alarm. I guess if there is excessive ripple, and I was overcharging (cooking) the batteries, that would be the explanation for being low on electrolite.

Edited December 6, 2011 by Mack E7 400