Catalina45

I have been fighting a parasitic drain on the battery and determined that when the battery isn't hooked up it holds a charge. The alternator puts out between 13.7-14.2 volts just idling. I found the following test to check whether a diode is bad in the alternator but need help determining what the readings of my multimeter mean. I believe its telling me that I have a 3 milliamp draw on the battery but I am not sure. Can someone take a look at how the multimeter is set up and tell me the reading and whether this indicates that the diode/rectifier in the alternator is bad. If this is bad, a link to rebuilding the alternator would be greatly appreciated. Thanks for the assistance.

Bad Alternator Diode Test

Usually, a bad alternator diode will cause your headlights, instrument panel lights, or stereo display to flicker or dim and, sometimes, drain battery power overnight or much sooner.

A diode helps convert alternate current (AC) produced by the alternator into direct current (DC) by letting electricity travel in one direction—toward your battery and other electrical systems—and blocking current in the opposite direction—from your battery or other circuits to the alternator.

When one or more diodes in the alternator rectifier fail, they will prevent a continuous electrical supply to the electrical systems—dimming headlights, the radio display, dashboard lights, and other devices—and drain battery power after the engine has stopped.

• To check for a possible bad alternator diode, switch your voltmeter to a low setting on the AC (alternating current) voltage scale.
• With the engine running, touch the meter probes to the battery terminals—positive (red) meter probe to the battery positive terminal, and negative (black) meter probe to the battery negative terminal.
• Your voltmeter should read 0 AC volts.

The presence of even a small amount of AC voltage will indicate a bad diode, so you'll need to replace the alternator's rectifier or the alternator.

911LE

I just tested my alternator today and it put out less than .1 volt ac at idle with the probes on the battery. It's possible your rectifier is failing but you would need to have it tested further. Your multimeter is not capable of testing the amp output of your alternator. Most auto parts stores will test them for free. Do your drl's flicker or not maintain a constant light at idle?
I just rebuilt my alternator on my '05 but the steps are the same for all '01-'06
https://www.clublexus.com/forums/ls-...r-rebuild.html

911LE

I ended up sourcing my rectifier locally from a electrical rebuild shop (starters, alternators, etc.). Cost was $40. I also ended up reusing my old brush holder and brushes because the ones I received from my online order were incorrect. Don't order from Maniac motors on eBay. Everything they sent me was wrong. If you are trying to source parts the Denso alternator part number is 104210-4000. The voltage regulator is different between the '01-'03 (3 pin connector) and the '04-'06 (4 pin).

Catalina45

Thanks for responding and its good to know that the multimeter isn't capable of the test. No the DRL's and all lighting remains constant at idle.I talked to a local alternator/starter shop today and they can complete a full diagnostic and if the alternator needs to be rebuilt the total with labor (includes new bearings, brushes, rectifier) is $247. They will rebuild my alternator on-site and have been in business 40 plus years. The diagnostic of $120 is waived if the alternator is rebuilt. The primary issue is a parasitic draw that I just can't identify but they said that it could be the rectifier and if it isn't they would "quickly" isolate the issue. Since I eliminated all fuses I don't know how quick it would be but they assured me that they would limit the labor to a maximum of the diagnostic fee. If it isn't the alternator and its a battery or some other parasitic draw it almost makes sense to rebuild the alternator as you eliminate the diagnostic fee and walk away with an "as-new" alternator and the problem is fixed (max cost $367). I did review your excellent article on how to rebuild the alternator and would consider doing it myself but if I spent $60 on parts and $120 to do the diagnostic test then the total out the door cost of $247 for them rebuilding my alternator (and doing labor) is probably worth the extra $60. I have to find the parasitic drain and unless you know of a "parts" store that does full charging systems test I am inclined to schedule an appointment with the alternator shop.

bradland

A rebuilt Denso from Rockauto is less than $120
Their S&H, and core return S&H, fees are very reasonable...

911LE

If you are handy I would skip the diagnostic and just rebuilt it yourself. Total cost is around $50. You could then buy a new battery for $85 (Costco) and everything will be new for $135. The shop I bought my rectifier from is also a Denso reman dealer and he said they are NOT built with OEM parts. Remanufactured alternators meet OEM specs but that doesn't mean everything is replaced. Most failures are the voltage regulator so that is replaced if that is the fault. As long as everything else meets specs it is reused. You may be buying a "new" reman alternator that most parts have 100k miles or more on it. Sure it got a "guarantee" but Chris Farley explained that pretty well in Tommy Boy.

Catalina45