ECU reports voltage pulled down to 12.0V

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I have an intermittent problem with the voltage dropping to 12.0V and revs coming down to 460rpm in D while sitting at the lights. Sometimes, the voltage will drop below 13V but shifting it to N brings it back up to 13.6V. Otherwise, when driving the voltage is normally between 14.1 to 14.4V (but may drop to high 13s).

I am monitoring this through the OBD port using the Torque Pro app on my phone.

The revs gets low enough to the point that it feels like the engine is about to stall. The battery is 5 years old and the last battery test when the fault first occurred shows that the battery is still healthy and the CCA is still quite high.

The fault has occurred with and without the aux battery (Arkpak) connected.

Have I got an issue with the battery, alternator or something else?

[ravenhard Member Find all posts View Profile Close ravenhard]

.sorry. Repied to wrong post

[mjrandom Out of control poster! Find all posts View Profile Close mjrandom]

Which is first do you think, revs dropping or voltage dropping? I suspect it is the former and the issue lies with something connected to the V6. If you had a diesel I would be looking at the SCV...

[sunny120 Junior Member Find all posts View Profile Close sunny120]

I had the same thing occur a few months back, just happened the once. Could hear the Redarc SBI dual battery solenoid click and when looking at the battery voltage gauge it was showing that there was no charge going to it. Thought nothing of it back then. After coming back from Cape York, it happened quite routinely, sitting at traffic lights, the revs would drop down and would stop charging (going by the dual battery volt gauge). I've just installed a new alternator and it has fixed the problem. I sent the old alternator to my auto elec, they had it on the bench tester for quite some time but couldn't fault it (brushes, solenoids etc all ok). Anyway, to cut a long story short I took a punt and had the voltage regulator of the alternator replaced. When retested it was showing better voltages and a better amp output reading at low rpms than it had previously.

The SBI solenoid light now stays on for much longer than it used to with the new alternator installed (used to cut out after about 1 hour, car has not been moved today from 6:30am and both batteries are still connected), I'm guessing that the old alternator was pumping out the voltage but not quite enough amps at low engine rpms to fully recover the battery. I could be totally wrong. By from what I have seen I can't explain it any other way. I can't explain why the engine RPM's drop though at its still happening, but it is not concerning me at the moment as it doesn't appear to me like its wanting to stall. Hope this is of some help to you.

FWIW I've also cleaned MAF sensor and throttle body. Checked O2 sensor values which are still within specs. Had exhaust gas analysed which showed all the gases to be within specs. Used Wurth petrol system cleaner and Wurth LBW400 system to clean the intake side of things. Installed twin tipped platinum plugs.. You name it, its been just about all done. Still can't get it to stop dropping idle speed. Could be a stepper motor problem, but from ECU readouts its performing as it should as with all the other electrical things. Won't look too much further into it unless it starts to stall the engine I guess.

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Which is first do you think, revs dropping or voltage dropping? I suspect it is the former and the issue lies with something connected to the V6. If you had a diesel I would be looking at the SCV...

Both at the same time.

[Guest Close Guest]

I had the same thing occur a few months back, just happened the once. Could hear the Redarc SBI dual battery solenoid click and when looking at the battery voltage gauge it was showing that there was no charge going to it. Thought nothing of it back then. After coming back from Cape York, it happened quite routinely, sitting at traffic lights, the revs would drop down and would stop charging (going by the dual battery volt gauge). I've just installed a new alternator and it has fixed the problem. I sent the old alternator to my auto elec, they had it on the bench tester for quite some time but couldn't fault it (brushes, solenoids etc all ok). Anyway, to cut a long story short I took a punt and had the voltage regulator of the alternator replaced. When retested it was showing better voltages and a better amp output reading at low rpms than it had previously.

The SBI solenoid light now stays on for much longer than it used to with the new alternator installed (used to cut out after about 1 hour, car has not been moved today from 6:30am and both batteries are still connected), I'm guessing that the old alternator was pumping out the voltage but not quite enough amps at low engine rpms to fully recover the battery. I could be totally wrong. By from what I have seen I can't explain it any other way. I can't explain why the engine RPM's drop though at its still happening, but it is not concerning me at the moment as it doesn't appear to me like its wanting to stall. Hope this is of some help to you.

I have a dual sense VSR. When the volts and revs drop, I look at the voltmeter attached to the Arkpak and it too is showing 12.0V. The battery in the Arkpak is otherwise showing fully charged once rested after a drive at 12.7-12.9V.

[ravenhard Member Find all posts View Profile Close ravenhard]

I thought I would ask here instead of starting a new thread. I've recently had the same issue where while driving in getting 14.4-14.5v but while idle or at stop I'm only getting 12.0-12.2 on the voltmeter. I've got HBKs booster diode and a red arc solenoid so lately I've been hearing it popping as the bolt drops and it opens. Never hear it open before only just recently

So is my battery farked or alternator not charging?

[Guest Close Guest]

I thought I would ask here instead of starting a new thread. I've recently had the same issue where while driving in getting 14.4-14.5v but while idle or at stop I'm only getting 12.0-12.2 on the voltmeter. I've got HBKs booster diode and a red arc solenoid so lately I've been hearing it popping as the bolt drops and it opens. Never hear it open before only just recently

So is my battery farked or alternator not charging?

Looks like we have something in common

[sunny120 Junior Member Find all posts View Profile Close sunny120]

I kept an eye on the battery gauge on the way home from work. At start up both batteries 14.1V, freeway speeds 13.9V, stop/start anywhere from 13.6-13.9V. Drops to 13.5V when idle speed drops to 500rpm. Goes back up between 13.6-13.7V at 650-700rpm. My second battery used to stay at 12.8V and start battery drop to 12V when the idle speed dropped to 500rpm. Hopefully the new alternator has fixed it.

Similar thing occurred to a D4D at Cape York, same symptoms with voltage dropping out intermittently, but the alternator carked it out on the tracks. He's since put a 130A alternator, removed diode and is getting 14.5V pretty much constant from what I've been told.

[Lewis120 Lurker Find all posts View Profile Close Lewis120]

Hey guys, I've been having this issue - voltage drops to low 12's at idle and stalls unless i keep them up when stopped. The car kicks over ok after it stalls. Has anyone determined if this is an alternator problem or something else? Happy to replace the alternator if so. Thanks!