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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>http://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.
hey i lost the bolt that grounds the battery to the engine block lol. i guess i misplaced it. anyways do you know which bolt to get at ace hardware as a replacement?
 

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Discussion Starter #42
hey i lost the bolt that grounds the battery to the engine block lol. i guess i misplaced it. anyways do you know which bolt to get at ace hardware as a replacement?
Well it actually mounts to a bracket and the bracket mounts to the block. I believe it is a 10mm or 12mm bolt but I'm sure to be honest. I would just grab several metric bolts about 1" long.
 

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Well it actually mounts to a bracket and the bracket mounts to the block. I believe it is a 10mm or 12mm bolt but I'm sure to be honest. I would just grab several metric bolts about 1" long.
i went to home depot and bought a M10-1.25 all they had were the 20mm length ones so i just put a washer under it to take some slack out and seams to be just fine.
 

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HI Jasonm4,
Thanks for your detailed information. Would you happen to know if new battery could cause 150 amp alternator fuse to blow as now it appears to have crack in middle of just that fuse on the fusible block?
Thanks for reading this and any help you can give me. My 250 IS sits stranded in my own garage now with second new battery that doesn't make it start! It was working fine until three days ago when it had the first instance of not starting but since battery was original from 2007, I thought it needed replacement. But why won't car start now even with new battery?
Any comments you have to share are greatly appreciated.
Susan
 

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HI Jasonm4,
Thanks for your detailed information. Would you happen to know if new battery could cause 150 amp alternator fuse to blow as now it appears to have crack in middle of just that fuse on the fusible block?
Thanks for reading this and any help you can give me. My 250 IS sits stranded in my own garage now with second new battery that doesn't make it start! It was working fine until three days ago when it had the first instance of not starting but since battery was original from 2007, I thought it needed replacement. But why won't car start now even with new battery?
Any comments you have to share are greatly appreciated.
Susan
I'm not sure, usually the alternator fuse only blows when the battery is hooked up backwards by accident. Have you been able to test the fuse to verify it is indeed bad? It could potentially cause starting/running issues if the alt is out of the loop.
 

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Please help!

HI Jason,
Thanks for writing back. If I post a photo, could you tell if the alternator fuse is blown? Or else can you please tell me how to test if the alternator fuse is blown? Is your vehicle also a 2007 IS? If it is that would make it easier for you to check out a photo of my fuses in the black box near the firewall on the passenger side to see what you think.
What other problems could cause my car not to start after new battery installed? It definitely wasn't hooked up backwards unless the manufacturer labeled positive and negative wrong which I doubt! What you even heard of a car not starting after new battery installed when it seemed like it just needed a new battery? I am just trying to trouble shoot what is going on with my car as it has never had problems before and gave no notice of this. It had the original battery which made it eight years old so expected that it would be in need of replacement. I have had the old battery tested and was told it definitely needed replacement. Car has low mileage so I can't think of anything else that would be causing it not to start!
Thanks again for listening! I will try to take a good photo now and post it soon. I am not quite sure how to send a photo though. Could you please give me instructions? I have a few good photos of this.
Susan
 

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I might as well post this in here, I'm not getting anywhere to fast on my own. I've got an '02, completely stock as far as I can tell, although I'm not positive that the PO wasn't messing about. Good optima blue top battery. Bad ballast on passenger side. Here's my problem:
Car starts fine and runs great aside from this problem. I was city driving one evening and noticed my battery light flickering, especially when making a turn from being stopped(turning the steering wheel at low revs) The volt gauge on the dash was showing me sub-12v so I assumed I was running off of the battery without help from the alt, aka bad alt. Got home without trouble, put 'change alternator' on my mental list of things to do during the holiday, and kept pushing my luck. Next time I started the car up, it seemed back to normal on the volt gauge so I continued driving it with mild trouble of the same sort off and on. Seemed to be happening consistently when I was driving at night (headlights/fogs on) using accessories, heater, rear defrost, heated seat.....finally decided I'd had enough and I'll just replace the alt. I've been down the dying alt route too many times to want to get stuck somewhere. Bought a lifetime alt from advance auto, installed and turned in the factory unit as a core. Few days later driving at night, same shit. Returned new lifetime alt for another new lifetime alt, drive, same shit again. Bought a new battery just to try it, same result so I started testing the system >
Start up, battery reads ~14.4v, rev up and goes to around 14.6v. Turn on heater full blast, dips a little but comes right back up. Start turning accessories on one at a time, rear def, hazards, wipers, heated seats, headlights, high beams, and it recovers after each one, down to about ~13v, where it seems to click over to running without the alt, dropping to ~11.7v with accessories on and ~11.9v once everything is off. Once it has 'clicked over' to this drop, the voltage doesn't recover when you rev, it drops slightly. To me it's acting like a relay is taking over, but I have no idea which it would be. If I shut the car off and leave it for 5 minutes or so, it resets itself back to normal operation, starts fine and runs back up at 14.4v. The only thing that's out of place is that while testing I've blown the passenger side(R) 15a fog light fuse twice. I pulled the connector and tested the plug, got a beep telling me there's continuity between the red/yel wire and the wht/blk. Also the same for the marker light in the bumper that comes from the same section of harness, continuity between the green and wht/blk, and obviously continuity between the grounds of these plugs. I looked at a wiring diagram I found online and it shows the DRL resistor in line on that circuit, so I disconnected the plug and tested the unit across the pins, came up with .8 ohms. That's where I stopped basically, my hands were cold and I couldn't find a spec for resistance on my phone in a few minutes of searching. Only other thing to note is that my A/C light blinks, if I turn on the heat it comes on automatically so I press once to shut it off, stays off for a few seconds then comes back blinking. I'm not positive that these are related, but if I can't find any problems with the fog light it's where I'm going to look next. Any insight would be awesome. Cheers
 

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That sounds like a bad regulator but you've eliminated that with two new units. Does the voltage go up at all in higher RPMs when it hits sub 12v levels? The AC blinking is odd, did you try a full load up test with every system on except to the heater/AC and see if it drops below the minimum test threshold?
 

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I guess it could be a second bad unit, but I can't test it besides pulling it and taking it over to be bench tested. Taking the car over would be a waste of time. I should say, I could test it. I was just hoping to not have to again. I think I am going to pull it and take it over, can't hurt I guess right. I'll just reserve the right to be highly irritated if it tests ok Lolz
The voltage doesn't rise at all once it's clicked over to below 12v, it drops slightly with the revs.
I do need to try load testing it without turning on the heater/AC, but I'm guessing it won't be enough to trip it without the load of the blower running. It's really too bad that they're linked, that's soooooo damn annoying
 

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Progress update:
Fog lights, turn signals all check out ok. I was mistaken in my previous statement thinking the fog light was blowing a fuse. The bad passenger side ballast was blowing it's 15A fuse, so I unplugged the connector to it and will leave it off until it gets replaced.
The current alternator on the car checks out, passes all tests listed here, so I've basically ruled it out. The only thing I found new was on the 3 wire plug. The center wire, red with blue stripe, is only getting 11.85v with the key in the 'ON' position. So the regulator isn't getting full juice? The battery was at 12.35v at that point. Now I have to figure out how/where to chase that issue down. Anyone care to chime in?
 

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I'm getting a 1.9A drain. Pulled every fuse from each box on both sides inside the car and both boxes on either side under the hood. No change.

Any other suggestions? I pulled the relays too except 3 I couldn't disconnect.

Not wanting to go to the dealership for this....
(car is stock)
 

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I'm getting a 1.9A drain. Pulled every fuse from each box on both sides inside the car and both boxes on either side under the hood. No change.

Any other suggestions? I pulled the relays too except 3 I couldn't
disconnect.

Not wanting to go to the dealership for this....
(car is stock)

1.9A is obviously way way too high. You will.have to trace it out, follow the positive battery lead to the nearby jbox. Did you full the higher amp fuses too? I would download a copy of the diagnostic manual, which is available on the stickies. A bad alternator with bad diode leakage could cause this but seems unlikely, however, it is one possible route. So you have the EFI, Radio#1, and Dome pulled? Sounds like a load of a light bulb or something, surely enough to kill the battery within hours. Don't take it to the dealer, you just need to verify what is pulled and dig deeper. You should see 0.050A after 5 minutes, not 1.9A.
 

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I pulled every fuse I found....but I did them one by one. Is there a difference if I pull a bunch instead?

Yes, I assumed this was my fail of something I plugged in so those were the first tests but no luck.

Would the alternator be failing? What's a good way to unplug it?
 

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I pulled every fuse I found....but I did them one by one. Is there a difference if I pull a bunch instead?

Yes, I assumed this was my fail of something I plugged in so those were the first tests but no luck.

Would the alternator be failing? What's a good way to unplug it?
I had an Alternator power diode assembly go bad once and it drew lots of amps when hot, and flattened the battery overnight. I suggest you disconnect the main power lead to the alternator if you cant find another way to disconnect. Good luck.
 

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I pulled every fuse I found....but I did them one by one. Is there a difference if I pull a bunch instead?

Yes, I assumed this was my fail of something I plugged in so those were the first tests but no luck.

Sorry for the late reply, there are main and sub fuses. They are located by the battery and kick panels. I would pull one main at a time or each individual until the current drops. You had a 1.9A draw which is equivalent to a 24 watt light bulb on continuously.
You NEED to make sure you find that draw and get it out of there or your new battery will die within hours. Remember there are certain fuses that draw car off, such as the EFI, radio #1, etc. Needs to stabilize under 50mA, that's a must.

Would the alternator be failing? What's a good way to unplug it?
It was a bad battery problem after all. Apparently Optima's are not what they used to be :(

Thank you all for the help.
You can find out with a good DMM and using the tests provided. Test for diode leakage(which can cause a draw), especially with a hot engine. Check your grounding and other tests. Worst case, you'll have to pull it for Bench test, which will also only additionally test for load output.

I don't think it's your battery, unless the load test says it has failed. As long as you have a D34-78(yellow) or like, and it's stored to full charge (12.6v+) then you shouldn't have problems. I have ran that battery for the last 4 years so far and my last one lasted 5½ years. But a hard parasitic ground will kill any battery in a short amount of time.
 

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I am pretty sure I did the test right so either my meter is crap or I don't know. Dealer had to do a recall so I let them diagnose it and they said it was pulling 0.4 amps and the battery did not pass the load test. Using Optima Red here and it only lasted 8 months. Maybe I'll try a Deka or Odyssey next time.
 

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I am pretty sure I did the test right so either my meter is crap or I don't know. Dealer had to do a recall so I let them diagnose it and they said it was pulling 0.4 amps and the battery did not pass the load test. Using Optima Red here and it only lasted 8 months. Maybe I'll try a Deka or Odyssey next time.
0.4A is still very unacceptable and no matter what battery you use will die within a week if you let it sit. My diagnostic for a stock IS300 is 0.050A, five hundredths of an amp. 0.4A mean you have an excessive amount of draw, no battery will work and is NOT the problem.
 

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Jason,

I just bought my daughter a '99 RX300 and while driving it tonight, I noticed the headlights would dim periodically and then come back up. I thought I heard a slight click in the passenger footwell, but I can't be sure. After a 30 minute drive home, I tested the battery and alternator best I could.
Headlights on high and AC blasting:
Engine at idle 13.52v
Bring throttle up to 2k rpm(guessing) the voltage drops to 12.6 and then comes up to 13.57v again.
Engine off, battery warm 12.75v

What do you think is happening? Faulty regulator?

Update: I bought and installed a TYC alternator from rockauto and now the voltage is spot on all the time at 14.4vDC
 
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