Question about 1998 GMC Jimmy

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Alternator Charging Problem- 1998 GMC JIMMY 4.3

I have a problem with the alternator not turning on after starting the vehicle.  After I start the vehicle the battery gauge stays at around 12 volts and the Battery/Charging idiot light stays on.  At times it takes anywhere from 15 seconds to 20 plus minutes for the alternator to kick in and the battery gauge shoots up to around 14 volts and the idiot light shuts off.  This problem never happens in freezing temperatures and never on morning startups, but always happens on a hot summer day after starting and stopping the vehicle throughout the day.  I have noticed that while the problem exists, and the idiot light is on, if I connect a battery charger to the battery and put it on the 200 amp setting the alternator immediately kicks in and the idiot light shuts off.  It seems light like there is a communication problem that is not relaying a signal to the alternator/regulator to turn on.  I have installed a new/remanufactured alternator and purchased a new battery, but the problem still exists.  I have had this problem for years and it seems like just recently it has become worse and is starting to leave me stranded as at times the alternator will not kick in and the battery drains right out.  I am wondering if the computer might be defective or I was also informed that the cluster may be defective as the battery gauge may not be sending a signal to the computer.  Any advice would be greatly appreciated.

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  • 3 more comments 
  • johnsolar May 08, 2009

    The voltage regulator is in the alternator, which was already changed and problem still exists.  Thanks. 

  • Samuel Charles Spriggs May 11, 2010

    Yes, a bad ground did come to mind.

    Another standard question: was the battery fully charged (12.3 - 12.8 volts) each time the alternator was replaced? If not, this can damage the alternator -- usually this precipitates a catastrophic failure, but it's possible it could create any number of mysterious, more subtle alternator behaviors.

  • Samuel Charles Spriggs May 11, 2010

    You will probably brush this off, but from years of experience, symptoms like this usually get a lot of parts thrown at them and in many cases the solution is deceptively simple.

    Has anyone checked all relevant electrical wires / connections (harnesses / screws / nuts / etc.) for corrosion / damage / looseness / missing insulation?

    This is where I would start.

  • Dar
    Dar May 11, 2010

    It obviously isn't your gauge since it is leaving you stranded. It's definately not charging, sometimes. I am wondering if it could be something to do with your ignition switch. If not that i would carefully inspect your terminals on the alternator. It sounds like a partially grounded terminal.

  • Samuel Charles Spriggs May 11, 2010

    First question, is the voltage regulator in the alternator or is it a separate component?



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  • GMC Master
  • 14,036 Answers

Check alternator wire .make sure its fuse is tight .and check fuse link.also check all grounds.

Posted on May 09, 2009

  • Jonah Oneal May 09, 2009

    look at the voltage regulator wires.



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Vehicles: any failing to keep its battery charged.

A vehicle unable to charge its own battery has one of 4 problems:
(a) alternator failure
(b) voltage regulator failure
(c) battery failure
(d) wiring problem between battery and alternator/voltage regulator.

One most modern vehicles (including 2002 Lexus RX300 - 2WD and AWD), the voltage regulator is an integral component of the alternator and is not separately serviceable.

In the US, one can get a free "charging system diagnosis" from the popular auto parts chains: AutoZone, Advance Auto Parts & Pep Boys. You needn't remove any parts from the car to get this diagnostic, since they can attach a diagnostic meter to the charging system in the parking lot. This diagnostic aid will tell you exactly which component has failed - battery, alternator or voltage regulator.

In case the vehicle is immobile, one can DIY (do it yourself) the diagnosis.
(a) inspect the wiring for corrosion/loose connections/loose connectors/etc.
(b) check alternator belt/pulley - if drive belt is properly turning the alternator pulley (no slippage/misrouting/etc.), then the mechanical tests are complete, and you'll need to continue testing the electrical performance of the charging system components.
(c) first component to test: battery
DIY test 1: remove battery from car and put battery on a 120VAC automotive battery charger and charge it fully (or just check it in the car with motor off, since the car's charging system is a type of automotive battery charger).
test parameter: a fully charged lead-acid automotive battery should read 12.45 volts on a VOM/DMM
DIY test 2: disassemble battery out of car after driving it to one of the auto parts chain stores (Advance/AutoZone/Pep Boys) for a free battery test. These testers will test the battery under load, which is not possible with just a DMM.
(d) if wiring is good, and battery tests good under load, then
the failed component is the alternator/voltage regulator - by process of elimination.
(e) DIY test 3: direct alternator/voltage regulator test (car must start and idle successfully to perform this test)
Start the car, and put a VOM/DMM across the terminals of the battery. Since the car is running, you'll be reading the output voltage of the alternator and not the output voltage of the battery. The acceptable ranges for alternator/voltage regulator output are:


Most alternators that are charging properly should produce a voltage of about 13.8 to 14.2 volts at idle with the lights and accessories off. Always refer to the vehicle manufacturer's specifications. Many Asian vehicles, for example, have higher charging voltages of around 15 volts.

When the engine is first started, the charging voltage should rise quickly to about two volts above base battery voltage, then taper off, leveling out at the specified voltage.

The exact charging voltage will vary according to the battery's state of charge, the load on the vehicle's electrical system, and temperature. The lower the temperature the higher the charging voltage, and the higher the temperature the lower the charging voltage. The "normal" charging voltage on a typical application might be 13.9 to 15.1 volts at 77 degrees F. But at 20 degrees F. below zero, the charging voltage might be 14.9 to 15.8 volts. On a hot engine on a hot day, the normal charging voltage might drop to 13.5 to 14.3 volts.

Here are the full specs for installation of the 2002 Lexus RX300 alternator - you may be able to check these specs yourself (with a torque wrench), or pass them along to your mechanic.

Note: the VIN 8th digit should be "F" for the 2002 Lexus RX300 (2WD & AWD)

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Glossary of acronyms
DIY = do it yourself
DMM = Digital Multimeter
DOHC = Dual Overhead Cam
SFI = Sequential Fuel Injection
VOM = Volt Ohmmeter

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2 Answers

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Nov 01, 2011 | 1998 GMC Jimmy

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Jimmy would not start, voltmeter read 9. After jumping battery, engine started but voltmeter did not go above 9. Battery symbol did not light up. Alternator or battery with high resistance?

sounds either like your alternator is bad, if it still goes dead then i would go with the alternator, other wise a cell or two could be bad or shorted in the battery.

Jun 25, 2010 | 1998 GMC Jimmy

1 Answer

My 96 jimmy has a good alternator and had a good

you may have a bad starter. pull it and have it checked.

Feb 06, 2010 | 1998 GMC Jimmy

1 Answer

All of the bells and whistles keep going off even when the key is not in the ignition? The battery keeps not charging? Any ideas

start the vehicle and remove the pos(+) wire from the battery while running, if it dies it is tell you you have a bad alternator

if my info has been helpful, please remember to leave good review. you can contact me at

Oct 26, 2009 | 1998 GMC Jimmy

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