How To Test The Alternator (2001-2002 4.7L Dodge Dakota)

TEST 2: Checking The Continuity Of The BATT (+) Cable

In this test step, we're gonna' check the continuity of the alternator's battery circuit. This circuit is the one that delivers the alternator's current output to the battery.

This wire is the black with grey (BLK/GRY) wire that connects to the alternator's stud with a nut.

The purpose of this test is to check the inline fusible link that protects this circuit.

If the inline fusible link is blown, your test result will indicate no-continuity in the circuit.

These are the test steps:

1. 1

   Disconnect the battery negative (-) cable terminal from the battery negative post. The positive cable remains connected.
   
   IMPORTANT: Don't continue to the next step without first disconnecting the negative cable from the negative battery post.

2. 2

   Place your multimeter in Ohms mode.

3. 3

   Connect the red multimeter test lead to the BATT (+) stud on the alternator. The BLK/GRY wire is attached to this stud with a nut (see the illustration above).

4. 4

   With the black multimeter test lead probe the center of the battery positive post.

5. 5

   You'll get one of two results.
   
   1.) If the inline fusible link, protecting this circuit, is blown, your multimeter will indicate a reading of OL (which means over limit). In other words, there will be NO continuity.
   
   2.) If the inline fusible link is OK and not blown, your multimeter will register an Ohms reading of 0.5 Ohms or less. In other words, there will be continuity.

Let's take a look at what your results mean:

CASE 1: Your multimeter registered continuity. This is the correct test result and tells you that the inline fusible link protecting this circuit is OK and not blown.

If the alternator is still not charging the battery (let's say you've already replaced the alternator and it didn't solve the problem), take a look at: TEST 3: Testing The Electronic Voltage Regulator Output.

CASE 2: Your multimeter DID NOT register continuity. This result tells you that the 8 gauge inline fusible link is blown and this will keep the alternator from charging the battery.

As I mentioned earlier, in this test section, this 8 gauge inline fusible link is part of the BATT + wire. It's on the end of the Bat + wire that connects to the starter motor solenoid.

Your next step is to check and replace this inline fusible link (if applicable) and retest. Replacing this 8 gauge inline fusible link (if blown) should solve your no-charge condition. You'll have to investigate the reason this inline fusible link blew, since they don't get blown for no particular reason.

TEST 3: Testing The Electronic Voltage Regulator Output

If you've reached this point, you have:

• Checked that the battery's voltage, with the engine running, is at 12.5 Volts and decreases when an electrical load is applied (TEST 1).
• That the BATT (+) circuit's inline fusible link is not blown (TEST 2).

The next step now is to make sure that the PCM's Electronic Voltage Regulator (EVR) is activating the alternator.

For a detailed explanation of how the EVR works, take a look at this section: The Basics Of The Electronic Voltage Regulator (EVR).

This is what you need to do:

1. 1

   Disconnect the battery negative (-) cable terminal from the battery negative post. The positive cable remains connected.

2. 2

   Connect the multimeter's black test lead to the generator field (GEN FLD) wire of the alternator's 2 wire connector.
   
   This is the DK GRN wire of the alternator's harness connector.
   
   NOTE: The alternator must remain connected to its harness connector. So you'll need to use a back probe or a wire piercing probe to connect your multimeter's black lead to the GEN FLD wire (see: Wire Piercing Probe).

3. 3

   Set your multimeter to Volts DC mode and connect the red multimeter test lead to the battery's positive (+) post.
   
   At this point, reconnect the battery negative (-) cable to the battery negative post.
   
   Before you continue to the next step, make sure that your multimeter leads/wires are not gonna' get tangled with the engine's serpentine belt.

4. 4

   Start the engine and notice the voltage output of the multimeter.
   
   The voltage value will fluctuate a little and this is normal.
   
   NOTE: There's no specific voltage number to give you or that you should expect because the EVR's pulse-width modulation of your Dodge is unique to the actual operating conditions and charge level of your Dodge's battery.

5. 5

   Have a helper turn on all accessories possible like the headlights, rear window defroster, A/C, radio, etc.
   
   Your multimeter should now show an increase in the voltage number. This value should be higher than the value you saw when the engine was idling and with everything off.

6. 6

   Have your helper turn off all the things he (or she) turned on in step 5.
   
   Your multimeter should now show a decrease in the voltage number. This value should be lower than the value you saw when the engine was idling and with everything on.
   
   NOTE: Keep in mind that if the EVR is good and doing its job, the voltage value your multimeter registers will fluctuate as it increases and decreases and this is normal. In other words, don't expect the voltage number to increase and decrease in a steady linear manner. The important thing to see here is that the voltage values increase and decrease as you apply or remove the electrical loads created by the headlights, rear window defroster, etc.

Let's take a look at what your test results mean:

CASE 1: Your multimeter registered an increasing/decreasing voltage as you applied and removed the electrical loads. This result tells you that the electronic voltage regulator (EVR) inside the PCM is working and trying to control the alternator's amperage/voltage output.

This test result tells you that the alternator is defective and needs to be replaced only if you have:

• Checked that the battery's voltage, with the engine running, is at 12.5 Volts and decreases when an electrical load is applied (TEST 1).
• That the BATT (+) circuit's inline fusible link is not blown (TEST 2).

CASE 2: Your multimeter DID NOT an increasing/decreasing voltage as you applied and removed the electrical loads. This result usually tells you that the EVR is bad and that the PCM needs to be replaced.

Before you run out and replace the PCM, you need to:

1. Check that there isn't an open-circuit problem in the GEN FLD circuit between the PCM and the alternator's harness connector.
2. That the alternator's 2-wire harness connector isn't damaged or broken.
3. That the alternator is good by having it bench-tested at your local auto parts store.
   • New or rebuilt alternators can be defective right out of the box and this happens a lot!
4. Check all of the PCM's Ground circuits by doing a voltage drop test on them and repairing any corrosion issues that the voltage drop test finds.
5. That the battery's terminals and posts are corrosion free.

Now, if the above is beyond your diagnostic skills, don't hesitate to get a professional tech's opinion and/or advice.