If your car has the battery light shining nice and bright, once you start its engine, there's a good chance that the alternator has failed. The cool thing is that alternator can be tested with a simple multimeter and it's a very easy test. In this tutorial I will show you how do it.
Contents of this tutorial:
NOTE: This tutorial applies to quite a few 2.2L Ecotec equipped GM vehicles. All of these use the same alternator. These are the: Chevrolet Cavalier and Classic; Oldsmobile Alero; Pontiac: Grand Am and Sunfire. To make sure this tutorial applies to your specific vehicle, take a look at the ‘Applies To:’ box.
You can find this tutorial in Spanish here: Cómo Probar El Alternador (2002-2005 2.2L Alero, Cavalier, Grand Am, Sunfire) (at: autotecnico-online.com).
Symptoms Of A Bad Alternator
Cranking your car's engine to get it started places a pretty heavy load on the battery. Eventually, cranking the engine would completely discharge the battery if it weren't recharged. So, once the engine starts, it's the alternator's job to recharge the battery and have it ready for the next engine start.
The starter motor isn't the only thing that needs battery power/current. Other things that place an electrical load on the alternator are: the fuel pump, air conditioning system, exterior lights (headlights, brake lights, turn signals), etc. Here again, it's the alternator's job to meet their electrical demand (once the engine is running of course) while recharging the battery.
By now I'm sure that you're seeing what an important and critical component the alternator is to your car. When it fails you'll see one of the following symptoms:
- The charge light (also known as the battery light) will be shining nice and bright on your vehicle's instrument cluster.
- Whenever you turn on the headlights (night driving), they glow very dim.
- The car won't crank. It will only crank and start if you jump start your 2.2L Ecotec equipped GM vehicle.
- 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 very first thing we'll do, to see if the alternator has failed, is to check the battery's voltage with the engine running.
If the alternator is OK and doing its job, you should see a battery voltage of 13.5 volts to 14.5 volts DC.
If the alternator has failed, then you're gonna' see a voltage of about 12.5 volts DC. This voltage value will decrease the longer the engine is running.
If you don't have a multimeter and need to buy one, check out my recommendations here: Buying A Digital Multimeter For Automotive Diagnostic Testing (at: easyautodiagnostics.com).
These are the test steps:
Crank and start your 2.2L Ecotec equipped GM car and select Volts DC mode on your multimeter.
Probe the positive battery terminal with the RED multimeter test lead.
With the black multimeter test lead, probe the negative battery terminal on the battery on your 2.2L Ecotec equipped GM car.
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 2.2L Ecotec equipped GM car.
OK, let's interpret your multimeter test results:
CASE 1: Your test result indicates 13.5 to 14.5 Volts battery voltage with the engine running. This voltage test result tells you that the alternator is working (charging the battery).
No further testing is required, since this multimeter test result eliminates the alternator on your 2.2L Ecotec equipped GM vehicle as BAD.
Now, if you're having to jump-start the car 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 car, 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 tells you that the alternator IS NOT charging the battery.
This result usually tells you that the alternator has failed and that it needs to be replaced. But I suggest that you check one more thing before you run out and buy it: TEST 2: Checking The Battery Circuit Inline Fuse.