Let me begin by saying I don't know an amp from a watt. Several times in the last few days my car has just stopped. Attempts to restart would not even crank the motor. There was electricity for lights, horn, etc. The first time, after a 45 minute rest (battery recovery?) the car started and ran for about 4 minutes. It would not restart. At about this time, I was subjected to a police tow for $200. On arrival home, I found it would start, and I was able to move it to its parking space. I then attached my code reader, I got 3 messages all of which ended with the suggestion the alternator was bad. I ran an alternator test and got 11.84 volts. I put my charger on the battery and in the morning, it started right up. I put my code reader on and got a reading over 13 volts and notice that was within "acceptable limits". Today, it failed at the local compost center. Fortunately, I met a guy not only willing to jump me (which easily started the car) but to also follow me home and provide another jump after another failure (we left cables connected about 10 minutes to provide some charging). Getting home I ran another alternator test and got a voltage reading varying between 7 and 9 volts. I have tried starting the car with the headlights on to see if they dipped. They do not seem to.
My question, is there any other test I should I make or is it time to accept that the alternator is bad? All checks of the battery indicate it is "good".
'08 XC70 Power loss, alternator?
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Faust
- Posts: 394
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- Year and Model: xc70 2008
- Location: MA
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I found this at ROck Auto, lengthy but I thought worthwhile
The First Things to Check
RockAuto
When the battery goes dead, the condition of the battery and the alternator are two of the first things to check. However, do not assume that if the battery is good then the alternator must be bad and the cause of the problem. My 1979 Chrysler 300 still has its original, never disassembled alternator. I have lost count of how many new batteries and electrical problems the car has had over the decades. Here are a few tips on how to use common tools to diagnose charging system problems to prevent unnecessarily replacing the alternator. These are general suggestions that may not apply to every car. Rely on your car’s repair manual (found under “Literature” in the catalog) for vehicle specific instructions.
Using a multi-meter, measure the voltage across the battery posts with the engine off. It should be 12 or 12.5 volts. If it is less than 12 volts, then the battery needs to be charged, something is draining the battery or the battery cannot hold a charge and needs to be replaced.
If the battery voltage is around 12 volts, then start the engine and again measure the voltage across the battery posts. It should have increased to 13 or 14 volts if the alternator is working and charging the battery. (Note: The computers on some newer vehicles will not raise alternator output to 13+ volts unless the headlights or some other system that draws a lot of electrical current is switched on first.)
If the battery voltage did not increase with the engine running, then verify the alternator and battery have good electrical connections. Make sure the battery cable terminals are tight and free from corrosion. Look for loose connectors or frayed cables. Use the multi-meter or a test light to verify the body of the alternator is grounded (zero resistance between the alternator and negative battery post).
If the battery voltage is well above 14 volts with the engine running, then the alternator could be producing too much current and overcharging the battery. Maybe the voltage regulator (internal to some modern alternators) is bad. Or the battery is weak and a vehicle computer has temporarily raised the voltage limit. It might still also be bad connections or loose wiring. Some vehicle lights being brighter than others can be a symptom of this type of problem, because the alternator produces more energy to overcome the resistance of a bad wire or connection.
The condition of the alternator belt is the next thing to check. Of course make sure the belt is not broken. Also look for a belt that is loose and slipping. It would probably be making noise.
If in step 2 the voltage across the battery terminals was 13 to 14 volts with the engine running, then the alternator is properly charging the battery. That is good news, but there is another alternator electrical problem to check for. I know from personal experience with a Ford 5.0L. that sometimes an alternator can charge fine when the engine is running but drain the battery when the engine is off. It probably has something to do with the rectifier diodes in the alternator not properly blocking current from draining away from the battery. This problem may be intermittent. It certainly was on my Ford 5.0. Disconnect all the electrical connections from the alternator when the car is put away for the night. If the battery never goes dead with the alternator disconnected but goes dead when the alternator is hooked up, then that might point to an alternator diode problem. RockAuto sells replacement diodes for some alternators. The diodes are buried so deep inside many modern alternators that replacing the entire alternator is often the most practical option.
If the battery goes dead when the car sits (engine off) with the alternator electrical connections disconnected, then something else is draining the battery. Check first for the most obvious battery drains such as any lights left on (headlights, trunk light, ashtray light, etc.). After that it gets harder to track down the problem especially on modern cars. Newer cars have systems that are designed to stay on for various amounts of time after the engine is switched off. In the next newsletter, I will offer some tips on tracking down specific circuits that are draining a battery.
Finally, there are the mechanical alternator problems. Unusual screeching or grinding sounds might come from a bad bearing in an alternator. However, the noise might also be coming from a loose belt, misaligned pulleys or worn out belt tensioner. Use an automotive stethoscope to verify where the noise is coming from. Avoid damaging new alternator bearings by making sure the belt pulleys are aligned, the belt tensioners are good, the belt is not over tightened, the alternator mounting bracket is not cracked or that there is not some other mechanical problem.
The First Things to Check
RockAuto
When the battery goes dead, the condition of the battery and the alternator are two of the first things to check. However, do not assume that if the battery is good then the alternator must be bad and the cause of the problem. My 1979 Chrysler 300 still has its original, never disassembled alternator. I have lost count of how many new batteries and electrical problems the car has had over the decades. Here are a few tips on how to use common tools to diagnose charging system problems to prevent unnecessarily replacing the alternator. These are general suggestions that may not apply to every car. Rely on your car’s repair manual (found under “Literature” in the catalog) for vehicle specific instructions.
Using a multi-meter, measure the voltage across the battery posts with the engine off. It should be 12 or 12.5 volts. If it is less than 12 volts, then the battery needs to be charged, something is draining the battery or the battery cannot hold a charge and needs to be replaced.
If the battery voltage is around 12 volts, then start the engine and again measure the voltage across the battery posts. It should have increased to 13 or 14 volts if the alternator is working and charging the battery. (Note: The computers on some newer vehicles will not raise alternator output to 13+ volts unless the headlights or some other system that draws a lot of electrical current is switched on first.)
If the battery voltage did not increase with the engine running, then verify the alternator and battery have good electrical connections. Make sure the battery cable terminals are tight and free from corrosion. Look for loose connectors or frayed cables. Use the multi-meter or a test light to verify the body of the alternator is grounded (zero resistance between the alternator and negative battery post).
If the battery voltage is well above 14 volts with the engine running, then the alternator could be producing too much current and overcharging the battery. Maybe the voltage regulator (internal to some modern alternators) is bad. Or the battery is weak and a vehicle computer has temporarily raised the voltage limit. It might still also be bad connections or loose wiring. Some vehicle lights being brighter than others can be a symptom of this type of problem, because the alternator produces more energy to overcome the resistance of a bad wire or connection.
The condition of the alternator belt is the next thing to check. Of course make sure the belt is not broken. Also look for a belt that is loose and slipping. It would probably be making noise.
If in step 2 the voltage across the battery terminals was 13 to 14 volts with the engine running, then the alternator is properly charging the battery. That is good news, but there is another alternator electrical problem to check for. I know from personal experience with a Ford 5.0L. that sometimes an alternator can charge fine when the engine is running but drain the battery when the engine is off. It probably has something to do with the rectifier diodes in the alternator not properly blocking current from draining away from the battery. This problem may be intermittent. It certainly was on my Ford 5.0. Disconnect all the electrical connections from the alternator when the car is put away for the night. If the battery never goes dead with the alternator disconnected but goes dead when the alternator is hooked up, then that might point to an alternator diode problem. RockAuto sells replacement diodes for some alternators. The diodes are buried so deep inside many modern alternators that replacing the entire alternator is often the most practical option.
If the battery goes dead when the car sits (engine off) with the alternator electrical connections disconnected, then something else is draining the battery. Check first for the most obvious battery drains such as any lights left on (headlights, trunk light, ashtray light, etc.). After that it gets harder to track down the problem especially on modern cars. Newer cars have systems that are designed to stay on for various amounts of time after the engine is switched off. In the next newsletter, I will offer some tips on tracking down specific circuits that are draining a battery.
Finally, there are the mechanical alternator problems. Unusual screeching or grinding sounds might come from a bad bearing in an alternator. However, the noise might also be coming from a loose belt, misaligned pulleys or worn out belt tensioner. Use an automotive stethoscope to verify where the noise is coming from. Avoid damaging new alternator bearings by making sure the belt pulleys are aligned, the belt tensioners are good, the belt is not over tightened, the alternator mounting bracket is not cracked or that there is not some other mechanical problem.
2004 V70
1964 Plymouth Convert (small block)
1967 Dodge Coronet (big block)
1964 Plymouth Convert (small block)
1967 Dodge Coronet (big block)
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Vova585
- Posts: 558
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Faust, we are friendly group of Volvo owners and not Mephistopheles to start philosophical discussions in here. I have hard time understanding why you are looking for troubleshooting info at RocAuto. There are plenty of reputable dedicated yootube channels that cover this topic in depth. If you would refer to scanner danner, pine hollow auto diagnostic, sma, advance level auto diagnostic channels i would understand...but rocauto is not the place to look for advice. You can buy 1 month DIY subscription for alldata for $25 and have detailed info and wiring diagrams, but spare us of rocauto advices. I attached the link for video by SMA that covers alternator and has decent amount of education on basic concepts. If you would let us know that "hey guys, I tried this and measurement was 123....I then did the other test and measurement was 321...I have hard time to interpret it, please advice" I would understand and try to help further, but without you doing the investigation and reporting back, I see no point to continue this thread
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abscate
- MVS Moderator
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The Rock Auto advice is basically sound. You need a good battery to run these cars since 1999
You aren’t running “ off the alternator” when the engine is on, you are running “ through the battery”
Get a full charge on the battery, then start the engine and look for that 13.5+ volts showing the charging system and battery are in good health.
You need a voltmeter for this, not a usb dongle ..they cost about $20 for a basic one at a home supply store, in the electrical section
You aren’t running “ off the alternator” when the engine is on, you are running “ through the battery”
Get a full charge on the battery, then start the engine and look for that 13.5+ volts showing the charging system and battery are in good health.
You need a voltmeter for this, not a usb dongle ..they cost about $20 for a basic one at a home supply store, in the electrical section
Empty Nester
A Captain in a Sea of Estrogen
1999-V70-T5M56 2005-V70-M56 1999-S70 VW T4 XC90-in-Red
Link to Maintenance record thread
A Captain in a Sea of Estrogen
1999-V70-T5M56 2005-V70-M56 1999-S70 VW T4 XC90-in-Red
Link to Maintenance record thread
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