Question about 1995 Cadillac DeVille

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Battery volts low - sign comes on when driving and battery is drained - cannot start - will jump battery and start - battery volts low light comes on again

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  • cedarsocks Sep 05, 2010

    local mechanic has already checked both battery (new) and the alternator - they claim the system may be grounded somewhere - how do you reset computer system? Maybe that is the problem.



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There seems to be a no charge state in this case. I recommend checking the battery first, then, move on to the charging system. Use the procedure below to isolate this issue.

Wear protective eye wear and clothing and remove all jewelry when checking your battery and charging system. Jewelry is a good conductor of electricity and is not recommended. Most batteries wear out every 3 to 5 years and need to be replaced. Always replace your battery with an equal replacement battery to assure proper operation. Automotive batteries have a positive terminal (red), negative terminal (black). Electricity is stored in the battery and then supplied to the vehicle when the engine is not running. While the engine is running the vehicles alternator charges the battery for future use. (Note: never disconnect the battery while the engine is running). To check a battery surface voltage, remove the positive terminal protective cover. Connect the positive side meter lead (red) to the positive side battery terminal. Connect the negative (black) side meter lead to the negative battery terminal. With the vehicle not running and the car sitting over night the battery voltage should be between 12.5 and 12.8 volts.(You will need to use a voltmeter for this testing procedure). If the voltage is not up to specs, replace the battery asap. If the battery is ok and showing good voltage readings; Move on to the alternator drive belt and amperage test.

The alternator is rotated by a drive belt, which is, driven by the vehicles engine crank shaft pulley while it is running. Electrical voltage and amperage are generated to recharge the battery and supply voltage to the electrical system of the car. The alternator is held in place with mounting bolts. There is a main electrical wire on the rear of the alternator that supplies voltage to a main voltage junction box. If your alternator is not charging properly, your battery will slowly drain down from operating all the electrical systems in your car and stop the car from running. Most non charge states will be the cause of a loose belt or a low tension rate, due to a mis-adjusted alternator. Make sure you have enough tension in the belt for full rotation of the alternator pulley.

Next, you will need to check the alternators output with the Amp meter.

Testing the amperage output of an alternator is good for measuring the amount (not the level) of voltage the alternator can produce. This test can be tricky because if the alternator is weak it can still show it as producing amperage(False reading); Which is good, but if the voltage is low, it will still allow the battery to go dead. To check the amperage output of an alternator an amp meter will be required. Once the meter is connected start the engine. Next; Turn on all electrical accessories and raise the engine idle to about 1300 RPM. The alternator should produce the max amperage it was designed to produce. Example: a 90 amp alternator should produce about 88 amps. An alternator cannot sustain maximum output for long periods of time. If the alternator is forced to operate at maximum output it will overheat and fail(due to a failed regulator). An alternator is designed to operate at max amperage output only for a reasonable amount of time. Once you have verified the amp readings, check the voltage. To check the voltage, Connect the voltage meter lead the same way you would in a battery static voltage check, Start engine (do not drive). At engine idle, the voltage should be between 13.6 to 14.3 volts. If not the alternator may need replacing.

Posted on Sep 05, 2010

  • Michael Masters
    Michael Masters Sep 05, 2010

    The pcm or engine computer can be reset by a certified code reader(scan tool) This would be the proper way to achieve results. If you do not have a GM certified code reader, i would suggest to pull the negative battery cable for 5 minutes. This will force the computer to reset. All stored codes and alerts will be wiped. The last method is quite crude, but it will be your only option if you cannot acquire a code reader.

    With that said; I would check the tension rate on the alternator drive belt and verify that the voltage regulator is functioning as designed. only do this is the low charge light appears again after the resetting procedure has been administered.

  • Michael Masters
    Michael Masters Sep 05, 2010

    Additionally; Check the field voltage sensing cable for corrosion and make sure all the corresponding grounds are not loose and corroded, as well. If the grounds are nice and tightly secured and the sensing cable is in good condition; Replace the voltage regulator. If you have any codes to post, please post them asap.



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