Good day fellow G37 drivers,

I have owned my 2011 G37x sedan (AT, barely 30k miles on it) for about a year now. Previously owned a G35x for almost 3 years so I'm starting to know these a bit, but I'm no car mechanic so my knowledge is limited in some areas. I've stumbled upon this forum several times which helped me track down and solve most of the issues I've encountered so far, until this one.

So here's what happens:
1. Push button to Acc, wheel and seat move to preset position
2. Push button to On, dash lights up etc, ready for startup
3. Put foot on the brake, try to start up vehicle: everything instantly shuts down, like someone had disconnected the battery. No attempt to crank whatsoever.

For the next, say, 15-30 seconds, no power or anything. Dash stays black, push button is not responsive. I usually step out, go around the back and open the trunk, by the time I get there the power is back because the trunk opens with the usual "beep" that goes with it. Then when I get back in, power is back and the car starts like nothing happened. The only indications are the stuff that are usually reset when the battery is disconnected (trip odo reset, climate controls back to default settings, etc).

This just happened to me twice in a week. The first time it happened I though it was a fluke but the second time got me a tad more worried. I used my car maybe 15-20 times between the two occurrences with no startup issue, so this is definitely an intermittent problem that could be hard to track down. Battery is barely a year old and just got through a typical Canadian winter with no signs of weakness so I'm ruling that out for now. Could this sound like theres a short somewhere? I truly have no idea where to start.
The only other post I've seen on this forum that points to a similar problem is this guy, but the thread is about 3 years old so I'm not reviving that, and the rest of the thread is of no help to me:
https://www.myg37.com/forums/g37-sed...ml#post4102369

I would definitely appreciate some help if anyone has a clue what could be going on! Thank you!

 

My old beater pickup does this every once in a blue moon and usually a simple tap of the battery cables and it fires right up.

Being that everything "resets" when you attempt to start the engine, indicates to me that- somewhere- the electrical connections between the battery and car are not secure.

First, I would check your battery posts and make sure the cable clamps are clean and tight. Also, check the battery ground cable where it bolts to the frame of the car (it is tucked under the fender, not easy to get access, but it is there).

While the battery is DISCONNECTED, I would check the positive battery cable where it attaches to the starter. You will likely have to securely raise the vehicle to do this. Again, the goal is to ensure that everything is clean and tight.

Assuming the above is all good, then you have to start looking at ground connections and the like.

Then there is the obvious question: did you fully check for water leaks?

 

Hey, thanks for taking the time to answer.

I did a visual check for leaks in the most obvious areas but could not find any evidence so far, although I'm not ruling this one completely out for now. I heard the sunroof seals are known to be leaky with time, I might have a look around. I will inspect the battery connections probably later today, as the problem occurred twice in a row for the first time this morning. It seems like it's getting worse every day. I will keep this thread posted. A friend of mine mentionned the BCM could be at fault here, does that make sense to you G37 wizards?

 

Yes, if there is a bad/failing power or ground connection, or if the BCM is getting wet.

Did you pull up the passenger front carpet?

 

Yep, I did a more in-depth investigation yesterday. BCM area has definitely not seen a single drop of water, so if that component is indeed going nuts, it's not because of leaks. Battery connections looked clean and legit to me. I admit I did not check the ground cable yet. I'm starting to believe it might be a faulty relay (either ignition switch or starter relay), I know these items are generally not prone to failure but the nature and intermittence of the problem makes me think it might be just that.

I am now taking a video every time I start the car now, so the next time it fails to start I will be able to provide that for understanding purposes.

 

Relay failures in these cars is rare. You may want to have a look at this thread. Glad to hear the BCM is bone dry- that is always a blessing...

 

I did stumble on that thread, some interesting info which I could use even though the issue is not exactly the same as mine, but the starter motor/solenoid connection is always worth a check in case it could be the root cause.

I finally got to film a faulty start in case it could help anyone figure out what's going on, here it is:


Shutdown at 0:10. Then I wait about 50 seconds (1:00 shows nothing happens when pressing start/stop), lose my patience and try to "trigger" the power back on by going around and opening the trunk at 1:18. 2nd startup at 1:38 is successful.

 

That is a BCM issue, not the starter/solenoid circuit so that can be ruled out. What happens when you just press the brake pedal and hit the button 1x? ie. does it start normally or...? Also, I noticed you have the ENTRY/EXIT feature turned on, I wonder if that might be contributing to the issue? Are you able to open the trunk using the dash release switch (when this happens)? Just throwing ideas out...

Aside from checking the wiring connectors (at the BCM) and checking for power/ground, there is not much else that can be done to diagnose the problem without the proper Nissan scan tools. I would:
1) disconnect battery;
2) unplug ALL of the connectors at the BCM- check for dirt, corrosion, pinched wires, water (even though leaks have been ruled out);
3) check the ground connections;
4) plug everything back up, reconnect battery, and go from there.

Maybe others will chime in with additional tips...