There is a LOT of discussion of the VVCS charging system used by Nissan all over the web. Mainly, that it kills batteries and is inadequate for aftermarket dual-battery systems. Many people seem to get around it by the super-easy, two-minute mod of unplugging the hall effect sensor at the negative battery post. By denying the ECM any load data, it defaults to the alternator's voltage regulator and charges at 14.4V all the time instead of reducing the charge voltage. This can be a critical, life-or-death issue for aftermarket AGM batteries because they require a higher charging voltage than a standard flooded or lead-acid battery. I'm not a fan. I'd like to throttle whatever stupid greenpeepee dunderhead cooked up the idea. Sparing a few drops of gasoline per year is not going to save the rainforest, improve the weather, or lower the ocean levels.

I've also read rumors that the hall effect sensor has a battery temp sensor in it that is being disconnected when it is unplugged. I'll need someone with more in-depth knowledge of Nissan electrical systems to confirm that fact before I hang my hat on it, though.

I drive Uber and Lyft in my 2015 QX60, so I have a lot of aftermarket electronics added and I spend a lot of time idling. Those add-ons are a convenient whipping boy for the uninitiated, but I have my doubts because they are all very, VERY tiny loads, but I have never completely discounted the possibility of "death by a million pinpricks". Because some of those aftermarket items are powered when the key is off, I bought an AGM deep-cycle battery (Optima yellow-top). Last year, my battery kept running down on me (before I knew what VVCS is), so I went through the expense (and INCREDIBLE heartache) of replacing the alternator with a brand-new, factory spec, Delco unit. This solved nothing, to my chagrin. Before too long, my Optima battery was deep-discharged so much and so many times that, even with a lot of great help from Optima, they replaced it under warranty for me. At that time, I coughed up the dough for an Optima Digital 1200 charger to keep my new battery healthy. Optima does not warrant replacements. That's a little irritating, but they can't just keep handing over new $350 batteries to someone when the problem is obviously not the battery.

I did relatively little driving in 2020 for the obvious, frustrating reasons. Demand for Uber and Lyft has come back with a vengeance in the last 6 months, but drivers are still being paid to sit at home by creepy Uncle Joe, so earnings are off the charts for people who are going back to work. In that time, I have noticed that I have to top up and condition the battery at least once a week with the Optima charger. Even still, after a lot of idling the battery will die and leave me stranded on a city street. This DOES NOT happen if it sits parked! The car is clearly running off of the battery when it should be running off of the alternator! I investigated adding an overdrive pulley to the alternator, until I learned what VVCS and quickly developed a seething hatred for it. With the air conditioner and headlights on, the VVCS was STILL only allowing 12.1-12.4 volts to the battery. AGM batteries REQUIRE between 13.6 and 14.8 volts, depending on the load (it should be higher when the car is in use).

As I opened with, a lot of people have found that simply unplugging the sensor at the negative battery terminal caused the voltage to go to 14.4 volts and stay there, with no trouble codes or other repercussions. There are even anecdotes of Infiniti and Nissan dealerships doing exactly that for customers with charging issues.

I started testing things out to see if this remedy would work for me. I followed arkham's razor and went with the simplest option first. Key off, unplug the sensor, check battery voltage. 13.3 volts. Start the car. By the time I got from the driver's seat to my meter under the hood, it had dropped to 12.4 volts. Maybe the ECM was still working off of the last input it had received from the hall effect sensor? I dunno. That's just conjecture. I let it cool overnight (I had been driving and it was midnight when I performed the first test). Then I removed the negative lug from the battery and connected the Optima Digital 1200. I left it to sit for a few hours for the charger to fully charge and condition the battery, and hopefully the ECM would "forget" the last thing it had been told by the sensor. By the time the charger had switched into maintenance mode, I reconnected the battery and the car had lost my seat presets and radio settings (hopefully meaning that it had also lost the last input from the sensor). I started the car with my meter on the battery posts and It jumped straight to 14.4V. I cheered. Within a minute, the voltage had dropped below 13V. I cried. As a sanity check, I turned off the A/C, DRL, and disconnected all of my aftermarket equipment. The voltage went up to just above 14V. Better, I suppose. As a further sanity check, I reconnected all of my aftermarket electronics. They are all such tiny loads that I am tired of debating whether they are the problem. The voltage was unaffected. I can FINALLY eliminate my tablets and cameras as the source of the problem. Turning the A/C on dropped the voltage to just below 13V. Adding the DRL caused it to go UP (slowly) but never get far past 13V. Basically, the voltage is still too low and is very erratic, regardless of the load. Why else would the voltage go UP when a load is ADDED?

I think the VVCS is still regulating the voltage, but is confused without the sensor. There is some discussion online about de-pinning or cutting the wire from the IPDM to the alternator, forcing the alternator to completely ignore anything the ECM tells it and charge at full voltage. This seems like a better option than unplugging the sensor, especially if there is a temp sensor in there as well. Unfortunately, I don't know and can't find the IPDM location or wiring info on a current-gen Pathfinder/QX60. Another guy named Jay has a very popular video on Youtube about it, but he leaves out a few pertinent details and is too vague to be entirely useful.

Forthcoming experience or knowledge would be appreciated.

TIA,

J

 

For the benefit of future googlers who stumble across this:
I finally got to the bottom of it. Simply disconnecting the sensor at the battery does not work on all models. I had to sever the wire between the IPDM and the alternator. Details here: