Alternator guage reads 9v, alternator checked good at parts store. any suggestions?

Asked by Feb 14, 2015 at 07:21 PM about the 1998 Jeep Cherokee 4 Dr Sport 4WD

Question type: Maintenance & Repair

My name is Jim, Wife was driving her 98 cherokee home check guages light came on,
alternator guage only reading 9v. she got home coasted into driveway. I got home charged
battery, started right up still only charging 9v. removed alt, had it checked at 2 parts
stores. Both said its good. Is there a fuse or a fuseable link I should check?

3 Answers

25,765

You may want to do a voltage drop test between the alternator's BAT (B+) terminal and the positive side of the battery circuit. Open or high-resistance can cause the diodes in the alternator charging circuit to fail, causing a loss of voltage supplied to the battery. connect a lead from a voltmeter between the battery positive post and the B+ terminal of the alternator, you should have less than 0.2 volts difference. (you can also do a voltage drop test between the negative battery post and the alternator housing).

1,235

I agree with Ken. If you do have a fusible link it would be connected with the positive battery cable, but if a fusible link is bad and there will be no voltage going to the battery. A good alternator when charging produces between 13.5 and 14.7 volts. hook up a voltmeter to the battery positive to positive negative to negative and start the car the battery should have at least 14 volts due to the alternator charging the battery then turn the headlights on and if the voltage drops below 12 volts then that's a sign the alternator is not charging probably.performing the voltage drop also check the integrity of the positive battery cable.

4,775

Hi the voltage regulator is controlled by the PCM (power control Module) and controls how much the alt will but out back into the battery you will have to test the voltage control wire back to the pcm for high resistance ...and check the battery for a bad cell that system needs to see 12volts into the PCM to get the correct voltage back out.... check the ground on the engine block ...make sure it didn't come loose or broken...and finally check the back of the cylinder head on the drivers side the head bolt is a stud style and the stud tends to pierce the wiring harness and wear the wires

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