GM diode/X2 power battery

I have a X2 power AGM battery and just installed the GM diode. Before I did I had my alternator tested at Auto Zone and it said the voltage regulator failed, however after putting in the diode and testing again it was good. What’s everyone’s thoughts on this?

 

There are several ways a voltage regulator can fail, so it will be hard to say without knowing how it specifically failed to begin with and what was the actual result of the diagnosis.

Also did it fail before your X2 install or was that diagnosed after the install?

It could be as simple as a grounding issue from corrosion that was fixed when you put in a new battery.

My understanding is the diode tricks the ECU into thinking the voltage is lower than it really is. If it wasn't a ground issue, my guess would be the alternator failed low as in it produced a voltage too low out of spec.

I don't work on automotive systems so it is possible there is some other blue smoke magic going on.

 

No it failed after I put the AGM battery in. But during the test the machine said turn on headlights and then it was holding around 13.6V but then said failed regulator but diodes good. I was just thinking maybe because the X2 requires higher voltage to properly charge it was giving a false negative on the test.

 

This helps to clarify the situation.

It is possible the AGM's lower internal resistance could have something to do with it.

A quick read says it is a common issue and can "fix" itself based on hot/cold weather.

Curious to see what more knowledgeable people say about this.

 

Interesting, I haven’t read the hot/cold thing. I’ll have to research more. Some people say I should just get a high output alternator, but doesn’t the computer in a Tundra limit the output anyways which is why I put the diode.

 

Hot/Cold may be a one off dealing with loose solder/connector.

Yes my understanding is the ECU controls the output. The diode causes the ECU to see a lower voltage which then signals to increase the voltage keeping the AGM happy.

 

Interesting article on alternators:
https://www.counterman.com/starters...iagnosis-can-lead-to-unnecessary-replacement/

 

I'm not understanding this diode thing.
A diode is essentially a check valve for current, only allowing it to flow in one direction.
If the AGM battery requires a higher charging current/charge rate, what would a diode do?
Can someone explain?

 

Explanation of a forum member:https://www.tundras.com/threads/charging-diode-for-agm-batteries.111426/#post-2876510
The diode lowers the battery voltage signal sent to the alternator voltage regulator, this raises the output of the alternator same amount.

I installed an Odyssey AGM battery a few months ago and didnt bother with replacing the alternator fuse with a diode. Plugged in a voltage meter and it was reading 13.5-13.7volts on idle.
Got curious about the diode and installed one. After installing a diode, voltage reading jumped to 14.3-14.7volts on idle.

 

I don't even have a AGM and run a GM diode. It stays just above 14 and never needs water. 27F Interstate does the job.

 

I run the X2 AGM with no diode for the past 3 years. No issues to report.

 

I've seen quite a few people report this. Makes me wonder why it works out for some to run with no diode and no trickle charger where others have the battery shit the bed. I would be curious to know.

 

May be the difference between daily driver duty and occasional use vehicles. If you start and run your vehicle every day and the battery gets a good charge, even if its lower than what it can handle, it will last a good long while. If its a weekend only type vehicle, and you run the batteries down while camping or whatever, and you're not getting a full recharge, then it may shorten the life of the battery. This is just a theory obviously.

 

I've been running an Optima AGM battery since 5/2022 (about a year and a half). No diode, no worries. It starts briskly every morning with no issues in 1 1/2 years.

If AGM batteries require baby sitting with diodes and trickle charging what is the advantage of even considering them? I've used AGM batteries on several motorcycles (some old enough that AGM batteries weren't even invented yet) all with absolutely no worries.

Dan

 

It’s just a little diode you swap out for a fuse, I wouldn't over think it just swap it out if you have a charging cycle battery over 14v so your battery stays topped off while your driving on the freeway or your alternator won’t click on. It’s honestly just a pre caution, I did this and noticed the difference immediately and I have a crap ton of lights and a ARB pump and an android deck and audio system in my truck. If your lights flicker when you crank then you know your batteries not topped off mine did before and it doesn’t now. I need my battery to stay optimal and letting your battery die because of that stupid voltage regulator Toyota puts on the ECU is just non sense.

 

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Diodes do have “resistance” or voltage drop across them, so a diode does have a different resistance across it compared to the fuse it replaces…essentially.

In the case of changing the alternators charge monitoring circuit from a fuse to a diode, the resistance only needs to change by approximately ~0.8 ohms to change the charging circuit voltage from mid 13V to mid 14V.

In normal operation, the ECU would see ~13.5 volts on that observed circuit voltage with a fuse in line, and charge the battery accordingly.

Add the diode with a small resistance/voltage drop across it and the ECU will see a false lower ~12.7 volt reading instead and let the alternator charge more to correct the “low” voltage reading. Since that low voltage reading is actually erroneous/modified, the net effect is an actual ~14.x voltage charge being emitted from the alternator, the ECU monitoring the alternator just doesn’t know it…but the battery does.

BTW, I’m running an X2 Power battery and I have the GM diode, but I’m not running it. I personally believe the battery isn’t meant to be charged by 14.6 volts constantly, as much as it isn’t meant to be charged at 13.4 volts. I think it really needs an occasional charging to 14.6 volts aka letting it charge at the lower voltage normally and throwing it on a charger once a month to bring it to 14.6 volts. But I’m too lazy to do that and opt to just charge it at the 13v level and let it ride. We’ll see.