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post #46 of 53 (permalink) Old 06-24-2012, 11:35 AM Thread Starter
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--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. 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.

this is where i am having my problem where you say 0.5 milliamps i am getting 12.3. so does this mean i am in need of a alternator? and is this the reason whu my battery light is on?

Last edited by jasonm4; 06-24-2012 at 11:46 AM.
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post #47 of 53 (permalink) Old 06-24-2012, 11:54 AM
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this is where i am having my problem where you say 0.5 milliamps i am getting 12.3. so does this mean i am in need of a alternator? and is this the reason whu my battery light is on?
I edited and quoted part of the tutorial so i wouldn't be quoting it all. You have a 12.3mA or 12.3A leakage to ground? Is that on a car that is fully warmed up(leakage can be more at higher temps)? That wouldn't be why the battery light is on i don't think. What are your other readings, such as running power at the battery and AC ripple?

If you didn't have a battery light before, then verify your battery terminals, bolted alternator connection, and harness are plugged in. The ECU is not seeing a charge hence the battery light.

'02 IS300 MSM LSD
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post #48 of 53 (permalink) Old 06-24-2012, 12:03 PM Thread Starter
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all other readings are as you described in the tutorial. so i seen no other issues except this leakage. and yes this is on a fully warmed up engine. the volt meter in the the car is reading proper level and with the multimeter i am getting a 12.6 with car off and 14.2 with car running. made sure plug was connected securely and is there a certain direction that the alternator wire needs to be bolted on? and i checked the fuses and none are blown. im thinking i need to take it the alternator out and take it down to autozone and have it tested.
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post #49 of 53 (permalink) Old 06-24-2012, 12:13 PM
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all other readings are as you described in the tutorial. so i seen no other issues except this leakage. and yes this is on a fully warmed up engine. the volt meter in the the car is reading proper level and with the multimeter i am getting a 12.6 with car off and 14.2 with car running. made sure plug was connected securely and is there a certain direction that the alternator wire needs to be bolted on? and i checked the fuses and none are blown. im thinking i need to take it the alternator out and take it down to autozone and have it tested.
The bolted alternator connection does point towards the rear when it's bolted because there's a support and cover for it(it lays over a support kinda), but really it doesn't matter as long as it's on there securely and has a good connection.

The leakage is a bit excessive and a free alt bench test sounds like a good idea. NAPA has the best bench testers fyi, but any place will verify it. Charging and battery voltage sounds good. This is rather strange.

'02 IS300 MSM LSD
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post #50 of 53 (permalink) Old 06-24-2012, 12:28 PM Thread Starter
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i will let you know what i find out once i get it tested.
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post #51 of 53 (permalink) Old 06-24-2012, 03:54 PM Thread Starter
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problem is fixed. come to find out one of the wires (white w/blue stripe) had come apart where previous owner had changed the plug and covered it up with heat shrink. reconnected the wire and battery light is off.
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post #52 of 53 (permalink) Old 06-24-2012, 04:03 PM
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problem is fixed. come to find out one of the wires (white w/blue stripe) had come apart where previous owner had changed the plug and covered it up with heat shrink. reconnected the wire and battery light is off.
Glad to hear! I thought it might be one of those three wires which is why i originally mentioned it. Better than buying a new alt! Nice job.

'02 IS300 MSM LSD
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post #53 of 53 (permalink) Old 06-24-2012, 04:10 PM Thread Starter
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yeah definatly better than buying a new alt. and thanks for the help jason. and thanks to cline on the crank timing gear.
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