DIY:CHARGING SYSTEM FULL DIAGNOSTIC(alternator/battery) - Lexus IS Forum
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post #1 of 71 (permalink) Old 02-19-2011, 05:38 PM Thread Starter
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DIY:CHARGING SYSTEM FULL DIAGNOSTIC(alternator/battery)

Enclosed in this thread is some detailed instructions on how to test your charging system properly using a handheld digital meter, one that is capable of measuring AC/DC voltage, ohm, and DC amps(capable of 400mA or 10A DC). You can pick up a Digital Volt Meter at any auto store, one capable of doing the job for $20 or so(Harbor Freight's $5 meter is fine too). If you've had battery issues or overall power problems, these tests will help diagnose any problems. ALWAYS TEST YOUR MULTIMETER ON A KNOWN LIVE SOURCE AS A TEST SUCH AS THE BATTERY.

PICTURES ARE INCLUDED AT THE BOTTOM TO SHOW HOW TO TEST(new attachment)

1. BATTERY. the first thing you need to check for is that you have a healthy strong battery. With a fully charged battery the voltage across the terminals should read 12.6V DC or higher with the car off. If the car has sat for a few days the voltage may drop slightly, but should never drop below 12.2V DC. To check, set the meter to Volts DC and put the red meter lead on the + terminal on the battery and the black lead on the - negative terminal. below is % of the battery's charge based on voltage. One last thing to consider is making sure the terminals are clean and tight as the cars electrical system can act strange simply if there is an issue with the connections.

No-Load Test Voltage Percentage(battery's charge % based on voltage tested)

12.60V+(100%) 12.45V(75%) 12.30V(50%) 12.15V(25%)

To check the condition of the battery under a load, put the meter on the battery terminals and have a helper start the car. The voltage should not drop below 9.5 Volts DC while starting.


2. GROUNDING. in order for the car to charge properly, there must be a good ground between your negative battery terminal, body/chassis and the engine block. There should also be good a good ground to the car's body, before the battery negative cable goes to the part of the engine block pictured below, it has a ground lug on it shortly after the battery terminal which also grounds to your body right under the battery tray(battery negative cable grounds the body and block/one cable). To test: using a meter, set the scale to ohm's setting. take the negative wire off of the battery. place one meter terminal on the battery negative wire and place the other lead on a clean metal spot on the engine block. the meter should read 1 ohm or less(continuity). anything higher would indicate the ground connection to the engine block is loose/corroded. always check your meter's accuracy by putting the meter's leads together and verify you have continuity(which may be 1 ohm or less). On the IS300, the ground is bolted behind the passengerside motor mount. Here's a pic of it...remember that a termination lug grounds under the battery tray first then here.



3. ALTERNATOR. There are four tests you can do while the alternator is in the car. The ultimate way to check the status of the alternator is by removing it out of the car and have it bench tested for free at most auto stores, but a handheld digital meter will be able to do most of the same tests. The only other thing a bench test does is a load test, but a clamp-on ampmeter can give you a rough idea of what its putting out(it will not tell you max rated ouput of DC Amps at max RPM). If you do have a battery malfunction indicator then that means there is a loss of running voltage and either the alt is out of the loop or bad. Battery indicator will not tell you if you have a bad battery, only when running voltage has dropped too low(from running off the battery perhaps).

If the alt needs pulled for a bench test or it's KIA, here's a great DIY made by homedepotmade>https://my.is/forums/f221/diy-alternator-swap-435652/

Note: Doing these tests when both the car is cold and at operating temperature is best because the heat will affect the readings. It is a good idea to do this especially for the AC ripple test, DC output, and diode leakage tests. The numbers will be higher because the diodes break down some when they're hot.

--DC VOLTAGE OUTPUT: With a fairly strong battery(12.5VDC+), the alternator has to produce 13.2-14.8 Volts DC to the battery terminals at idle(750RPM). This number will be closer to the lower end of the spec if it is at operating temperature. To check using a meter: set the meter to DC volts and turn on the car. turn on the headlights and A/C blower to high. Put the red meter lead on the + terminal on the battery and black meter lead on the - terminal on the battery. Check it at idle and at 3K RPM. The voltage should be 13.2-14.8 VDC. If it is low at idle but comes within range at 3K RPM, then your battery is weak and needs to be checked for voltage. If the battery is tested ok(12.6+ VDC) and the voltage is below 13.2VDC when the car is running idle, the regulator is bad(bad alternator). if the idle RPM's are below 700, then the regulator may also struggle to put out 13.2VDC or less based on the load(ie.headlights on plus A/C on, etc.).The IS300 should idle at 750 +/-50 RPM. numbers based on FSM.

--AC RIPPLE: alternators essentially produce 3 phase AC current and a six pack diode configuration converts the AC to DC current. Again, a hot or warm engine is best because the diodes can perform weaker when hot. An alternator should never produce more than 500mV or .5V AC under a load. To check you will need to turn the car on, turn on the high beams and heater blower switch on high. Using a meter, set the scale to AC voltage setting. place the red meter lead on the bolted wire connection on the alternator. place the black meter lead on the housing of the alternator or a clean good ground on the engine block. NOTE: Use EXTREME CAUTION as you will be testing near the moving drive belt. The safest way is to use alligator clips and clip them between the meter terminals and the connections you are reading from so you dont have to hold the meter lead tip at the bolted wire on the alternator. As mentioned, at any time the AC voltage exceeds 500mV/.5V, the diodes are bad and the alternator needs replaced.

--DIODE LEAKAGE: the diodes in the alternator prevent current from flowing backwards and only allow it to flow in one direction, thus creating DC current. Diode leakage can kill your battery over time very quickly as it puts an additional draw on the battery when the car is off. It's best to do this test on a hot alternator because diodes leak more when hot. To test using a meter: set the meter to DC amp scale and make sure the meter leads are moved on the meter to where they read current(usually this involves moving the red meter lead to the AC/DC amp plug). with the car off, take the positive wire off of the battery(this is done to avoid a short when taking the bolted + wire off the alternator). Un-bolt the battery cable at the alternator. Connect the positive wire back on onto the battery terminal, making sure the unbolted alternator wire is clear from any ground. put the red meter lead on the bolt connection(where you took the wire off) on the alternator and connect the black meter lead on the alternator wire that you took off. the current reading on the meter should indicate a few miliamps DC, typically should be around 0.5 milliamps or .0005 amps DC. anything more than a few miliamps(3mA/.003A or more) means your diodes are not blocking properly and are draining your battery when the car is off. after your done, take the + wire off the battery and then put the + wire back on the bolted connection. then re-hook the battery up. alternator needs replaced if readings are higher then mentioned as its putting a drain on the battery.

--AMPERAGE OUTPUT: if you have a clamp-on DC amp meter, then you can check the output of the alternator while the car's electrical system has a load and no load. set the clamp on meter to DC amps and start the car with everything else off except the engine. clamp the positive bolted wire coming off the alternator, USING EXTREME CAUTION as the drive belt is close. with just the engine running, the amps should be less than 10 AMPS DC. next, turn on the high beams and heater blower switch on high. take another reading for a few seconds. The reading should be 30 AMPS or more. Now these readings can change based on how good the battery's charge is. If the battery voltage is less then 12.6 VDC, the alternator may produce slightly higher readings. Numbers based on FSM.

--3 WIRE ALTERNATOR HARNESS: there are 3 wires that are in a harness that plugs into the alternator. One is a white w/blue stripe that is fed from the 7.5A ALT-S fuse and always has 12 volts to ground when the car is off or on. The red w/blue stripe wire comes off the 10A GUAGE fuse and should have 12 volts to ground when the car ignition is on only(for regulator). The last wire is a signal for the ECM and is a blue w/red stripe wire. On '01 this wire goes straight to E7pin26. On '02+ this wire goes to E6pin15. These connections are essential for the alt to function.

4. PARASITIC CAR-OFF DRAIN: This is the drain on the battery when the car is turned off. The diodes will leak more when the car is hot as mentioned, so a warm engine for testing is best. There is always a slight drain for the radio memory and ECU memory. Stock drain should be less than 70mA, but more on the order of 35mA, after 5 minutes. If it is higher than 70mA, it will kill your battery in less than a week if the car sits, or longer, depending on the draw. To check with a meter, first make sure that the car is off, all lights are off, all doors are closed, and everything is turned off. This is important as you risk blowing your meter's fuse if something is on. Set your meter to read DC amps(10A setting). Take the negative wire off of the battery. Put the red meter lead on the negative battery wire and the black meter lead on the negative post on the battery. Make sure not to remove the leads off of the connections for 5 minutes, if you lose contact then you will have to do it over again. Alligator clips may help so you dont have to hold them in place or risk losing a connection while waiting for the reading. watching the meter, you will notice that the meter will start around 300mA/.3A(or slightly higher) and after the ECU and modules go to sleep(about 3 minutes), the amp reading will drop to the constant parasitic draw. After 5 minutes if the amps still exceed 70mA or more, then you will have to start troubleshooting by pulling fuses and checking the load side of all of the fuses to the line side to find out why/where the draw is so high. (NOTE:If there is a direct short and the fuse is alredy blown, then you risk blowing the internal meter fuse or cause damage/injury)
CAUTION: MAKE SURE THE METER IS RATED TO TEST AT LEAST 400mA/.4A OR HIGHER. (most meters have a mA scale and a 10A scale. the 10A scale would be the better of the two settings to use).

CAUTION: NEVER REMOVE ANY OF THE BATTERY TERMINALS WHILE THE CAR IS RUNNING. DOING THIS CAN INSTANTLY KILL THE ALTERNATOR. THE BATTERY ACTS AS A BUFFER AND FILTERS OUT ANY SPIKES FROM THE REGULATOR, SO WITHOUT THE BATTERY, THE REGULATOR CAN BE DAMAGED!!!


Hopefully this thread will help those who have charging system/battery issues and dont understand the variables that can effect it. using a meter can be a alot easier than spending a diagnostic fee.
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Last edited by jasonm4; 03-25-2014 at 07:56 PM. Reason: added engine ground pic
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post #2 of 71 (permalink) Old 02-24-2011, 06:56 PM
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Great job Jason! This is exactly what we've been needing. I've seen a lot of threads that could have been answered by your DIY.

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post #3 of 71 (permalink) Old 02-24-2011, 07:53 PM Thread Starter
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Great job Jason! This is exactly what we've been needing. I've seen a lot of threads that could have been answered by your DIY.
Thanks Rey! I'm sure a lot of people will wonder why a DIY for something easy, but some don't realize all the variables that need to be right and can be easily checked. Tried to make it easy for any beginner. Also easier to cut and paste a link rather than write a book when someone is having issues. If it helps one person then it was worth making it to me.

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post #4 of 71 (permalink) Old 04-21-2011, 11:50 AM
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Yes saves re-typing the same stuff over and over

A few comments.

Multimeters.
Error Spec is always % of full scale, so use the lowest scale, Typ. 20V DC for Battery measurements.

A Harbor Freight Multimeter for $2.95 on sale is fine !!! I checked the specs.

Diode leakage can test fine yet be a problem. they will leak more, a lot more, when hot. This can and did discharge a running car with a 60A Alt on the freeway. Also discharged overnight when car put away hot.
Intermittent, and difficult to find. ( OK it was a Delco Alt. )

Always turn on the lights for a few minutes and watch the battery voltage, if it suddenly drops to 10.x volts you have a bad cell. Otherwise it tested fine at 12.6 V !!!

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post #5 of 71 (permalink) Old 04-21-2011, 12:24 PM Thread Starter
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Thanks for the added comments Ian! Very true that diode leakage can really show up at a higher value when the engine is at operating temperature.

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post #6 of 71 (permalink) Old 12-14-2011, 08:44 AM
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just took my battery to auto zone and got it tested,
results:
GOOD
Voltage 12.06V
Measured 365 CCA
Rated 585 CCA
Temp 60 degree F

they told me my battery is good, but your telling me that its not ( 12.06V), i took the battery off the car and took it in.
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post #7 of 71 (permalink) Old 12-14-2011, 08:57 AM Thread Starter
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Originally Posted by 08lexus350 View Post
just took my battery to auto zone and got it tested,
results:
GOOD
Voltage 12.06V
Measured 365 CCA
Rated 585 CCA
Temp 60 degree F

they told me my battery is good, but your telling me that its not ( 12.06V), i took the battery off the car and took it in.
Sure the battery may test good, but it is definitely low on a charge. The basic battery load testers look for two things and print out a paper telling you the status of the battery(if the cells are healthy) and also the state of charge. I guarantee that your results read GOOD-NEEDS RECHARGED. Just look at your CA and CCA, they are low, but that doesn't mean the battery is bad. It means it should be able to take a charge and it needs one. A fully charged battery would read 12.6 vdc or higher as well as higher cranking amps. Most of the time the people working at these auto stores don't know better. They just told you your battery is in a state where it should accept a charge but also needs charged up. Also, if they do more than one load test, obviously the numbers are going to drop. So.....take the car for half hour drive and then see what the voltage is after the car has sat for an hour.

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post #8 of 71 (permalink) Old 12-14-2011, 09:13 AM
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12V lead acid battery is 12V nominal
13.2 V full charge and 10.8V completely discharged.
So your battery is only half charged.

Check your Alt voltage with a fully charged battery, use a 6 amp charger, overnight is best, the charge will drop to almost nothing when its fully charged.
If its not in spec as above, change your voltage regulator.

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post #9 of 71 (permalink) Old 12-14-2011, 09:19 AM
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Very good post Jason. I would rep, but I can't again

Thanks a lot!
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post #10 of 71 (permalink) Old 12-15-2011, 07:26 PM
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Wow, great thread! I really needed the info. Thanx Jason.
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Wow, great thread! I really needed the info. Thanx Jason.
glad to hear it helped. did you find a problem?

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glad to hear it helped. did you find a problem?
I just read the thread and think there is a short somewhere in the dash. I'm gonna restart my search tomorrow morning. Thanks again.
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I just read the thread and think there is a short somewhere in the dash. I'm gonna restart my search tomorrow morning. Thanks again.
no problem. If you want l, you can start a new thread in the first forum if there's an issue. you must have a cluster issue or illumination more likely.

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Hey Jason, great writeup. I'm having battery issues on my 04 is300. If I leave my car sitting overnight, it has a hard time starting (barely starts) in the morning and if I leave it sitting for over 4 days it won't start at all. I've noticed when I remove my stereo this problem goes away. Now, I had my stereo replaced about 2 years ago with a aftermarket system using a metra wiring hardness thus maintaining the stock amp functionality. Furthermore after the install, my auto headlights stopped functioning properly in the sense that my headlights would turn on and turn off as they are supposed to while the car is on but they won't turn off automatically after I turn the car off. My audio installer tapped into the illumination and also performed a parking brake bypass during the install. I don't know if it could be that my stock amp is staying on even when I turn the car off? I was hoping you could give me some idea as to what the problem is and a possible solution. Thanks for you help.
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post #15 of 71 (permalink) Old 02-20-2012, 04:42 AM Thread Starter
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Hey Jason, great writeup. I'm having battery issues on my 04 is300. If I leave my car sitting overnight, it has a hard time starting (barely starts) in the morning and if I leave it sitting for over 4 days it won't start at all. I've noticed when I remove my stereo this problem goes away. Now, I had my stereo replaced about 2 years ago with a aftermarket system using a metra wiring hardness thus maintaining the stock amp functionality. Furthermore after the install, my auto headlights stopped functioning properly in the sense that my headlights would turn on and turn off as they are supposed to while the car is on but they won't turn off automatically after I turn the car off. My audio installer tapped into the illumination and also performed a parking brake bypass during the install. I don't know if it could be that my stock amp is staying on even when I turn the car off? I was hoping you could give me some idea as to what the problem is and a possible solution. Thanks for you help.
Are you pulling one of the radio fuses to remove the radio. Both the amp and radio are fed from the radio fuses, so it needs verified what it's drawing. Doubtful, but you could have a low battery and it can't take the parasitic draw from the radio or amp. So, you need to find out if one of the units is bad and staying on. If you have a meter that can read DC amps, put the meter lead in parallel between the open fuse socket and see what it is drawing, that way you'll know who if it's a weak battery or device(HU or amp) staying on. Do the parasitic draw test. Radio and ECU combined should be less then 50mA or. 050 Amps. See what radio #1 and radio #2 fuse are drawing.

I would also check the state of the battery to make sure it can take a 50mA load draw daily with no problem. Sometimes when batteries go bad, a slight draw can kill a weak battery. Have it load tested and lemme know what the radio draw is, using the guide in the OP.

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