Saab Battery And Alternator diagnosis

When your battery starts dying out on you it's time to get out the volt meter and do a few tests. It can be easy if you just know what your dealing with. I'm going to give you a few tests you can do with just a volt and a small amp meter. The amp meter only has to go up to 3amps to be useful in this test. As with most my articles I'm figuring you already know the basics of electrical and mechanics. Were going to make a few tests to eliminate or pin point possible causes of our dead battery. In the situation of a dead battery there are three basic possibilities the alternator has no output, your electrical system has a parasitic drain or simply your battery has gone bad.


Warning only perform these tests in a well ventilated area and wearing safety glasses. Removing your battery cable can cause sparks that can ignite explosive gasses given off the by the battery.

Your first step is to charge the battery. You can not make any accurate checks with a dead battery. Charge the battery till you get a reading of 12.6 volts or above. This test should be done with the engine not running. If you have charged the battery and just can't get the battery to 12.6 volts you have a bad battery and should replace it.

Once the battery is charged and you have the car running it's time to check your alternator. The alternator will put out up to 110 amps depending on your model. We will not be testing with an amp meter on this test though. An amp meter to get those high readings is costly. We will be checking the voltage at the battery with the engine running. If the proper voltage is there you will have the amps also. The reading you are looking for is something above 12.6 volts yet under 14.5. You should have something like 13.8 volts. This will depend on what electrical loads you have on (radio, lights, Fan). You should turn off all loads that you can for this test. If you find good voltage here you can move on to the parasitic drain test. If you find your voltage reading at 12.6 or less you have alternator problems. You should check the drive belt tension (engine not running). If this looks good you will have to make some electrical tests. If you drive a classic 900 you will want to check the ground strap to the alternator this black wire is known to break.This is the wire bolted to the alternator case and back to the engine block. If you have another model don't worry about this the alternator case grounds directly to the mounting bracket.Your next test is for Field voltage this is the small wire on the back of the alternator (usually green) marked DF. You should test this wire with the ignition on. You should find around 9 volts or so, but the main thing is you find some voltage if you have no voltage here your alternator will never start to charge. If this is your problem you will have to trace this circuit back through the battery light on your dash for this you should see your wiring diagram. Also test your B+ wire at back of the alternator (the large red wire). You should find approx. the same voltage on the B+ wire as your battery has in it, hopefully 12.6 volts. If your ground, field wire and B+ wire all come up good you have an internal alternator problem. One last thing you can do before you buy a new unit you can check your brush/voltage regulator this is the black unit in the back of the alternator held in by 2 small screws( see picture). If you pull this brush pack out you can examine for worn brushes. These are the 2 black carbon pieces you see as you remove the voltage regulator Min. length on these brushes should be no less than 5 mm long. Remember just because you find the brushes worn doesn't mean you don't have another internal problem, but I've repaired many old alternators just by replacing this unit.

Parasitic electrical drain on your battery is often over looked, but is a good test when battery problems arise. This is a simple test that can give you a lot of good info on your electrical system. For this test I recommend an Amp meter that will handle at least 3 Amps.What we will be testing is the amount of currant being used when your key has been removed from the ignition. There is normal drain about .03 amps. This is to keep the clock running, memory on ecu's and your alarm running. Sometimes when a part let's say your radio goes bad it can have an excessive drain, this is what we will be looking for. To run this test disconnect your negative battery cable and hook one lead of your amp meter to the negative battery terminal and the other to the cable. Do this with everything shut off and key out of ignition. The amp meter should be reading around .03 amps anything above .05 is getting too high. If you have a high reading it's time to find the problem component. This can be done by pulling fuses one by one until you loose the drain. Some trouble spots I've found are the trunk light left on, radio amps, alarms and cell phones. If you have a NG 900, 9-3 or 9-5 you will have to wait at least 20 minutes after hooking up the amp meter to get the correct reading. ( read this follow up article) These cars have computers in them that stay active up to 20 minutes after the the car is shut off so watch out for this. 9000 models with ACC also need time to shut down so give them 6-7 minutes and you should be OK. Classic 900 you should only have to wait a minute for the interior light to time off.

If you have tested the alternator voltage and parasitic drains and the tests come up good it's time for a new battery. Things to remember are, just because you find one problem doesn't mean you don't have two. I have seen many times when bad alternators have ruined batteries and so on. You may also have itermintant drains and alternator problems such as low output. You never know sometimes you will come up with the strangest problems that can cause alternator battery problems so keep an eye out and think about what your testing before you spend hours changing parts.

(This article is meant to educate a consumer,or as a guideline for professionals. You can cause serious damage to your vehicle and/or cause yourself injury. Only those qualified should attempt repairs. I do my best to assure that the above info is correct but take no responsibility for any damages incurred.)


Home - Email

Feel free to e-mail with any tech questions