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Half-start issue seems to be directly related to lower battery voltage, short trips, and restarting within a short time of shutting off.

It happened to me for my 2nd time in 2 years this past weekend. I shut the vehicle down after about 3 hours of driving. And then attempted to restart within about 30 seconds, unplanned but I had to move the vehicle.

I also tend to think it's when the brake and start button sequence is rushed or button not fully depressed for a solid 2 seconds. I likely jumped right back in and rushed the sequence, maybe even pushed both brake and button simultaneously.

Either way, our charging systems don't help and are bad for battery health. Look into bypassing the voltage sensor on the negative terminal.
 

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Sounds like vapor lock due to heat soak. I don’t own an armada but have been researching on this board in anticipation of purchasing later this year so I don’t entirely understand the 5.6 layout. But it’s common in some trucks, especially those with big engines stuffed into small places, to get much hotter AFTER they are turned off if there is no proper ventilation.

The fuel in the fuel rail will boil and vaporize causing an erratic and arrhythmic attempt at starting. This can often be prevented with a flimsy foil style heat shield or a little better airflow. If your problems are occurring from cold start disregard my suggestion, but this frequently occurs after leaving the hot engine for about 10-15 minutes. Much longer and the fuel with condense again.

The stop start button failing is a different issue to do with how the computer registers the engine is running I’d guess but I don’t know enough about Nissans to theorize. Either way, preventing the fuel problem should prevent the button issue.

I’ve especially seen these issues (in other vehicles) as the cooling system loses efficacy due to age or the weather gets hot, it’s very common in old Jeeps. I would expect this would be the first issue a mechanic would investigate, especially if the misfire codes are vanishing after their vapor clears the injectors and liquid fuel is flowing. If this is not possible due to the 5.6 layout please disregard but I wanted to put it out there.

-Joe
 

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Excellent theory and might be the culprit. Both times mine has done it have been after the engine is hot and during hot ambient temp.
 

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Here is my update on this problem.
In my case it has going on about a year.
Never knew when it might not start. Dealer never found any trouble codes. Service manger drove the truck for a week and of course it started right up every time.
I even managed to capture a short video on phone. But as service manager stated doesn't help without a trouble code.
eventually they did a battery test and found that even though it passed it was in the low end of the acceptable scale.
Had a new battery installed.
Then the service guy asked if I made many short trips, stop and go. Three or four miles to store then back home type driving.
He stated it takes driving about 10 miles to fully recharge battery and that several short trips aren't long enough to fully keep a full charge on battery.
Also there are many behind the scene features when parked that drain on the battery. Such as GPS, info for engine monitoring for starting, and instant on apps that all come on line as soon as you hit start the engine button.
Yes I do take many short trips of less than 5 or 6 miles.
Since then I try driving a little longer distances. Maybe add a few extra miles when going to store. That's ok cause wife and I love driving this thing.
It's been since April and have not had any false starts. Starts every time.
One last note, the many times I showed up at the service desk they always listened to me tried to solve this problem.
Great guys.
 

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So my 18 armada has done the same thing for a few months and finally it has happened at the dealership. They are going to look at all the systems and try to diagnose what the cause is. Fingers crossed something can be found since they were the ones starting it when it happened.
 

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So my 18 armada has done the same thing for a few months and finally it has happened at the dealership. They are going to look at all the systems and try to diagnose what the cause is. Fingers crossed something can be found since they were the ones starting it when it happened.
So my 18 armada has done the same thing for a few months and finally it has happened at the dealership. They are going to look at all the systems and try to diagnose what the cause is. Fingers crossed something can be found since they were the ones starting it when it happened.
Has the dealer had any luck figuring out what is causing the issue?
 

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So my 18 armada has done the same thing for a few months and finally it has happened at the dealership. They are going to look at all the systems and try to diagnose what the cause is. Fingers crossed something can be found since they were the ones starting it when it happened.
Any update on the issue?
My 2018 Armada Platinum with 45k miles just did this today, drove it for 5 miles, parked at restaurant for 1 hr and then went to start and had this issue occur. In my case I tried to turn the armada off but it kept engaging the starter again, mine didn’t die, instead finally just started running like normal after 45seconds.
 

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I have not had this issue happen again since I disconnected the sensor on the battery terminal.
Mine did it twice over the course of about 2 months in summer of 2020.

Since disconnecting the battery sensor we have put about 15k on the Armada, towed our 28' camper regularly (1 trip in excess of 2k miles), been to SC, Western NC, and VA. It has not happened once; long trip, short trip, hot or cold. I am going to chalk this one up as being directly related to battery voltage.

The short trips seem to be a trend for the problem to happen as well as heat, but I believe the heat just compounds the low battery voltage issue as the starter is less efficient when it's hot.
Short trips do not allow the battery to charge up after a start, but the real problem is that with the sensor connected your ECM is always keeping the battery charged at too low of a voltage anyway.

With the battery constantly maintained over 13 volts it can handle the shorter trips and repeated starts.
IMHO disconnecting the battery sensor has cured this and has zero adverse results.
YMMV, I am not a mechanic.
 

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I have not had this issue happen again since I disconnected the sensor on the battery terminal.
Mine did it twice over the course of about 2 months in summer of 2020.

Since disconnecting the battery sensor we have put about 15k on the Armada, towed our 28' camper regularly (1 trip in excess of 2k miles), been to SC, Western NC, and VA. It has not happened once; long trip, short trip, hot or cold. I am going to chalk this one up as being directly related to battery voltage.

The short trips seem to be a trend for the problem to happen as well as heat, but I believe the heat just compounds the low battery voltage issue as the starter is less efficient when it's hot.
Short trips do not allow the battery to charge up after a start, but the real problem is that with the sensor connected your ECM is always keeping the battery charged at too low of a voltage anyway.

With the battery constantly maintained over 13 volts it can handle the shorter trips and repeated starts.
IMHO disconnecting the battery sensor has cured this and has zero adverse results.
YMMV, I am not a mechanic.
Thank you @OBXPatrol that makes a lot of sense. I have read the same thing on forums for other Infiniti models as well. The sensor doesn't allow for charging until after 15 minutes of driving time. Is it possible to show a picture of the battery sensor that you disconnected from the ECM?
 

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@Len T it is a sensor that it attached directly to the negative terminal on the battery itself. There is only 1 harness that goes to this sensor. I'm sorry but I do not have an easily accessible picture at the moment. There is likely one in another sub-forum.

When plugged in, the ECM talks to this sensor and limits the battery charging to the minimal amount possible to maintain right around 13 volts. This is all done in the name of 1/10 of an increase in MPG. The problem is that batteries really need to charge around 14.2 volts. If you only charge to 13, your static voltage is usually 12.6 or lower. If you allow the alternator to charge to 14.2-14.5 your static voltage is always 13 or higher on a healthy battery.

If your battery is only at 12.6 static, once a load is applied it may drop to 11.8 or lower. Vehicle electronics in general do not like to see under 11.8. So in theory if the vehicle is attempting to start right on that threshold you could run into some pretty wonky effects.
 

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Hi, Just wanted to add that this same false start/ engine shuddering/ vibrating issue has happened to our vehicle. It's 2018 Armada platinum, first owners. First noticed in June 2021, around 53,000 miles. Since then it's randomly occurred two more times at different times of day (once was late evening, in hot Louisiana weather, other time was early morning). Each of the 3 random occurrences, my idiot self cannot seem to get my phone video rolling, so I can't record it! SO GLAD to see we're not the only ones have nearly identical symptoms.
 

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@Len T it is a sensor that it attached directly to the negative terminal on the battery itself. There is only 1 harness that goes to this sensor. I'm sorry but I do not have an easily accessible picture at the moment. There is likely one in another sub-forum.

When plugged in, the ECM talks to this sensor and limits the battery charging to the minimal amount possible to maintain right around 13 volts. This is all done in the name of 1/10 of an increase in MPG. The problem is that batteries really need to charge around 14.2 volts. If you only charge to 13, your static voltage is usually 12.6 or lower. If you allow the alternator to charge to 14.2-14.5 your static voltage is always 13 or higher on a healthy battery.

If your battery is only at 12.6 static, once a load is applied it may drop to 11.8 or lower. Vehicle electronics in general do not like to see under 11.8. So in theory if the vehicle is attempting to start right on that threshold you could run into some pretty wonky effects.
Hello @QBXPatrol, I have just one more question. Did you just unplug the wire harness from the sensor or completely remove the sensor from the negative terminal? Thanks again for your help.
 
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