Question about 1999 Chevrolet Suburban

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Charging system my 99 suburban is loosing voltage. both batteries are almost new (6.5 turbo diesel) but after about 10minutes of running ,1 battery starts dropping volts. the battery on the RHS stays at 14.7v, the alternater is charging at 14.7v, and the battery on the LHS drops to around 10volts, then after a while, the voltage drops too low and it shuts off. then i have to re-charge the batteries again. any ideas on what this could be?, thank you in advance

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If you swap the battery positions, does the problem move to the RHS ?

Posted on Feb 09, 2014

Testimonial: "hi ,no i swapped the batteries and now they are both reading 14.10volts. havent been for a big drive yet but any ideas why it would do that, thanks"


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Posted on Jan 02, 2017

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SOURCE: Charging problem on 2005 Suburban - gradual voltage reduction

This vehicle has a "Regulated Voltage Control" system. The computer reduces the charge voltage based on several parameters to improve gas mileage. Normally it shouldn't be a problem, but the computer will increase the voltage if you switch on the headlights. Also, if you're in Tow/Haul mode the voltage will increase.

Posted on Dec 01, 2009

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SOURCE: 2000 astro van Battery and alternater are both new

You may have a voltage drop in the battery feed to the Alternator through the fuse link and into the battery. Check the charge rate at the battery feed on the Alternator, it should be at least 13.8 volts, if it is, locate the fuse link and check it there on both sides of the link, if its still good, follow the cable back to the battery checking the voltage as you go. If you find that the voltage suddenly drops across a connection or the fuse link, remove and clean the connection or replace it if possible. If the voltage at the back of the Alternator is less then 13 volts, then the new Alternator may be faulty. If the voltage is higher then 15 volts, then the Battery feed to the Alternator is bad and MUST be fixed. Check these voltages with the engine running but watch out for moving parts ( fans etc). If you think the battery feed to the Alternator is bad, shut the engine down and recheck the voltage at the Alternator, it should be at least the same as it is across the battery. If there is no power to the Alt when the engine is off, start at the fuse link, checking for voltage and trace back to the alt until you lose the reading. If you get no voltage at the fuse link, track it back to the battery. The voltages at the battery and Alternator should be the same or only have a difference of half a volt, any more and you need to locate and fix the bad connection. DO NOT run the Alternator without the load of the battery for extended periods as this will damage the Alternator. The Alt needs the internal resistance of the battery to function correctly. If the voltages from the battery to the alt are correct, check the regulator wiring. If memory serves, there are two small wires to the alt which are in a small plug into the alt and one thick cable which connects to a bolt on the alt. The thick cable is the battery feed, the two small cables are the regulator feeds. One small cable operates the warning lamp in the dash cluster and the other is another battery feed which gives the regulator an indication of the charge rate AT THE BATTERY so if this one is missing the regulator will also cut out. The warning lamp wire serves as an indication to the regulator that the ignition is turned on and makes the alternator charge. This lamp should be on with ignition on but engine NOT running and should go out when you start the engine. If this lamp does not light up at all, suspect a broken or missing warning lamp connection or faulty regulator.A blown warning lamp bulb will also prevent the alt from working, this is because the bulb is fed with power and is grounded at the alt through the regulator and exciter diodes, feeding the regulator with power until the engine starts, then the alternator output essentially puts power to both sides of the diodes causing the lamp to extinguish. A diode is a one way valve for electricity and the regulator is inside the alt. If you suspect a faulty alt or regulator, remove them and have them checked by an autoelectrician. Unless you know what you are doing, DO NOT attempt to disassemble the alt as you can cause catastrophic damage and have to purchase a replacement alt. You may also void any warranty by disassembling the alt.. Undertake these tests and if you have any questions, email me here:

Posted on Dec 15, 2009

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SOURCE: 2001 Duramax 6.6 Turbo wont start

does the starer click when u turn the key,u could have a bad ground from the batt to the body

Posted on Dec 31, 2010

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