If you suspect that the alternator in your 4.2L V6 Ford full-size van isn't charging the battery, you've found the right tutorial.
Testing the alternator isn't difficult, and you don't need any expensive diagnostic equipment either. I'll show you how to test it with just a multimeter. With your test results, you'll quickly find out if the alternator is good and charging the battery or if it has failed.
Contents of this tutorial:
APPLIES TO: This tutorial applies to the following vehicles:
- 4.2L V6 Ford E150: 1997, 1998, 1999, 2000, 2001, 2002, 2003.
- 4.2L V6 Ford E250: 1997, 1998, 1999, 2000, 2001, 2002, 2003.
F-Series Pickups: You can find the alternator test for the F-Series pickups here:
- How To Test The Alternator (1997-2003 4.2L Ford F150, F250) (at: easyautodiagnostics.com).
WIRING DIAGRAM: The alternator circuit wiring diagrams for this tutorial can be found here:
- Charging Circuit Wiring Diagram (1997 4.2L V6 Ford E150, E250).
- Charging Circuit Wiring Diagram (1998-2003 4.2L V6 Ford E150, E250).
Symptoms Of A Bad Alternator
As you're already aware, the alternator's job is to charge the battery. This is a pretty critical task since the battery gets discharged significantly when the starter motor cranks the engine to get it running.
Besides charging the battery so that you can start the engine the next time, the alternator also provides electrical current to all the accessories that need to be turned on, like the headlights, radio, and wipers.
Unfortunately, the alternator isn't gonna last forever. Its internal parts, like bearings and brushes, wear out over time. When they fail, the alternator stops charging the battery. When this happens, you're gonna see one or more of the following symptoms:
- The battery light (charge indicator) will illuminate in your van's instrument cluster.
- The headlights are dim when the vehicle is running and they are turned On. They grow dimmer as time passes till eventually the vehicle stalls.
- The vehicle requires a jump-start, every time it's turned off, to start it.
- The battery needs to be constantly re-charged.
TEST 1: Battery Voltage Test With Engine Running
To get our alternator diagnostic under way, we're going to test the battery's voltage with the engine running.
If the battery in your van is dead, you'll need to charge it fully before you begin. The battery has to be charged enough crank the engine and then keep it running for at least 5 minutes while we perform the battery voltage test.
We'll check the battery's voltage with a multimeter. If you don't have one and would like to buy one, check out my recommendations here: Buying A Digital Multimeter For Automotive Diagnostic Testing (at: easyautodiagnostics.com).
NOTE: You'll be working around a running engine, so be careful and take all necessary safety precautions.
OK, let's get started:
- 1
Start the engine and let it idle.
- 2
Place your multimeter in Volts DC mode.
- 3
Check the battery's voltage with your multimeter.
- 4
The multimeter should register 13.5 to 14.5 Volts.
If it doesn't, don't worry about this just yet, continue to the next step. - 5
Turn on every accessory possible while observing the multimeter. Like the headlights, the A/C or heater (high blower speed), the windshield wipers, the radio, the rear window defroster, etc.
As each accessory comes on, they'll place a load on the charging system (alternator). - 6
The multimeter's voltage reading will decrease slightly and then stabilize around 13.5 to 14.5 Volts DC as each accessory comes on.
- 7
Let the engine run for about 5 minutes with all of the accessories on.
- 8
The battery voltage should remain between 13.5 to 14.5 Volts DC with all of the accessories on during the whole 5 minute duration.
OK, let's make sense of the readings that your multimeter recorded in the test:
CASE 1: Your multimeter registered 14 to 14.5 Volts from the start of the test to the end of the test. This test result lets you know that the alternator on your 4.6L or 5.4L Ford van is working like it should. No further testing is required.
CASE 2: Your multimeter DID NOT register 14 to 14.5 Volts from start to end and the voltage dropped to 9 Volts DC. This test result lets you know that the alternator is probably bad.
Probably bad? What I mean is this, around 90% of the time, you could stop here, replace the alternator and the problem is solved. To be 100% sure the alternator is bad, there are 2 more tests to do and I'll show you how to do them. Go to: TEST 2: Checking The Continuity Of The BAT + Circuit..
TEST 2: Checking The Continuity Of The BAT + Circuit
The charge that the alternator produces is delivered to the battery via the black with orange stripe (BLK/ORG) cable, which connects to the rear of the alternator with a nut.
Before the alternator's charge reaches the battery through the BLK/ORG cable, it has to pass through two inline fusible links.
It's not uncommon for these inline fusible links to get blown and prevent the alternator's output from reaching the battery.
In this test section, we're going to do a simple multimeter continuity test on this circuit to find out if the inline fusible links are okay.
If they are, then we can confidently conclude that the alternator's charge is being delivered to the battery, assuming the alternator is good.
These are the test steps:
- 1
Disconnect the battery negative (-) cable from the battery but leave the positive (+) cable connected to the positive (+) post.
IMPORTANT: Do not proceed to the next steps until you have done this first. - 2
Set your multimeter to Ohms mode.
- 3
Connect the red multimeter test lead to the stud shown in the photo above.
A BLK/ORG cable connects to the stud indicated by the arrow (in the photo above).
NOTE: Don't disconnect the BLK/ORG cable from the alternator. - 4
Connect the black multimeter test lead on the battery positive (+) terminal (at the battery).
The battery negative (-) wire must remain disconnected from the battery. - 5
Your multimeter will register one of two values:
1.) Continuity (usually an Ohms value of about 0.5 Ohms).
2.) No continuity (an infinite Ohms reading (OL)).
OK, now that the testing part is done, let's take a look at what your results mean:
CASE 1: Your multimeter registered 0.5 Ohms. This result indicates that the mega fuse is OK and not blown.
Now, there's just one more thing to check and you're done! The next test is to make sure that the alternator's voltage regulator is getting power. For this test, go to: TEST 3: Making Sure The Voltage Regulator Is Getting Power.
CASE 2: Your multimeter DID NOT register 0.5 Ohms, it registered OL. This result tells you that the inline fusible links are blown.
Check the inline fusible links. If they're blown, replace them and retest. More than likely, this will solve the alternator's no-charge problem.
Blown fusible links are rare. However, if they do get blown, you'll need to find out why, as they don't get blown without a reason.
These fusible links are connected to the starter motor relay. The starter motor relay (not to be confused with the starter motor solenoid) is located in the right front corner of the engine compartment.