Testing to see if the alternator on your 2.6L equipped Isuzu Pick Up (Amigo or Rodeo) is bad or not is probably one of the easiest tests that can be done with a simple multimeter.
In this tutorial, I'll show you how in a step-by-step way.
Contents of this tutorial:
Puedes encontrar este tutorial en Español aquí: Cómo Probar El Alternador (2.6L Isuzu Pick Up, Amigo, Rodeo) (en: autotecnico-online.com).
Symptoms Of A BAD Alternator
Your 2.6L Isuzu's alternator fulfills two basic requirements: One is to maintain the battery fully charged so that you crank and start the engine.
The other is to provide the electrical current for everything that requires it as you're driving your Isuzu down the road. What requires electricity? Well, think: radio, blower motor, headlights, fuel pump, etc.
So, when the alternator fails, you'll notice one or several of the following symptoms:
- The charge light (also known as the battery light) will be shining nice and bright on your Isuzu's instrument cluster.
- Whenever you turn on the headlights (night driving), they glow very dim.
- The engine won't crank. It will only crank and start if you jump start your Isuzu Pick Up (Amigo, Rodeo).
- The only way the car cranks and starts is if you charge the battery.
- The idle may get high when you come to a stop.
TEST 1: Battery Voltage Test With Engine Running
The get our alternator diagnostic under way, the first thing we need to do is confirm that it's not charging the battery.
This simply involves checking the battery's voltage, with a multimeter in Volts DC mode, while the engine is running.
If your Isuzu's alternator is working (and charging the battery), your multimeter should register around 13.5 Volts. If it isn't, then you'll go on to TEST 2.
NOTE: If the battery is completely dead in your Isuzu, you'll need to charge it up. The battery must be charged enough to keep the vehicle running for at least 10 to 20 minutes.
These are the test steps:
Crank and start the engine and select Volts DC mode on your multimeter.
Probe the positive battery terminal with the red multimeter test lead.
With the BLACK multimeter lead, probe the negative battery terminal.
Your multimeter is gonna' register one of two possible readings and they are:
1.) A steady 13.5 to 14.5 Volts DC.
2.) Or 12.5 Volts that will decrease the longer the engine stays running.
Put an electrical load on the alternator to further confirm that it's either charging or not charging.
You can do this by turning on every accessory possible (inside the vehicle). For example: Turn on the A/C or heater on high, turn on the windshield wipers, turn on the headlights, turn on everything and anything that uses electricity inside and outside of the vehicle.
Your multimeter will show you one of two things (as you turn on all of this stuff):
1.) The multimeter will register a nice and steady 13.5 to 14.5 Volts DC no matter what gets turned on or...
2.) It will register 12.5 V DC and this voltage will decrease more and more as you turn on stuff inside your Isuzu.
OK, let's interpret your multimeter test results:
CASE 1: Your multimeter registered 13.5 to 14.5 Volts. This voltage test result tells you that your Isuzu's alternator is working (charging the battery).
No further testing is required, since this multimeter test result eliminates the alternator on your 2.6L Isuzu Pick Up (Rodeo or Amigo) as BAD.
Now, if you're having to jump-start the vehicle to get it going then this test result points to a bad battery or a parasitic drain. A parasitic drain is tech-speak for something staying on (usually inside the vehicle, for example: a dome-light) and draining the battery while the engine is off.
CASE 2: Your multimeter registered a voltage that steadily dropped down to 9 Volts: This is a clear indication that your Isuzu's alternator IS NOT charging the battery.
Replacing the alternator at this point usually solves around 90% of the No Charge conditions on any 2.6L Isuzu around the world. That's right, you could stop testing here and say: ‘The alternator is fried’ and be done but I suggest two more easy tests to be absolutely sure it is defective. For the first test of the two, go to: TEST 2: Checking The Continuity Of The Bat (+) Cable.