No tachometer No Codes No start, and not a clue
 

When you have no start and no tach it's almost always a crank sensor, make sure to use ONLY an OEM or Hitachi sensor.

I have no clue why it started with the MAF unplugged, that's really odd.

I would start with the crank sensor, make sure to inspect the harness and wiring for any damage or contamination.

Also make sure your NATS/IVIS security light isn't solid red when cranking, that would indicate the BCM doesn't recognize the key in the ignition and the ECM won't fire spark/fuel.

Getting progress
 

Inspect the harness and wiring for damage or corrosion. If they look good then you probably need the throttle motor replaced but there are troubleshooting steps in the FSM you can follow to verify the proper voltage and continuity of the conductors back to the ECM.

Section EC, Engine Controls. Find the diagnostic trouble code in the table of contents and it will direct you to the proper page number.

https://nicoclub.com/archives/infiniti-g35-g37-factory-service-manuals.html

Thing is the throttle motor also includes the throttle position sensor. I suspect that code is generic for either of the circuits shorting out. There are instructions in the FSM under that diagnostic trouble code for how to unplug the harness on the throttle motor, then unplug the harness on the ECM, use a digital multimeter to verify a continuous circuit (nothing wrong with the wire).

If the circuit is good and you have that code then the ECM is reading that SOMETHING is causing a short circuit and that leaves just the components inside the throttle motor.

I would try to look around at local pick-n-pull lots to see if you can find a cheap replacement throttle motor.

As for the IPDM, yes you could definitely also have something wrong with it but the throttle circuit doesn't go through the IPDM so it's not causing that code. I would remove the IPDM, remove ALL the relays and fuses from it, thoroughly inspect/clean, leave in a box of rice overnight to dry up any dampness. Put everything back in, reinstall, and make damned sure the cover is on properly because that's what usually causes that type of corrosion.

If find anything that's severely corroded inside then clean it as best you can, sandpaper sticks work good and so do mini precision files, apply a tiny bit of dielectric only to the component you plug in (fuse/relay/etc).

Hey Fellow G drivers!

Looks like my first post here is reviving an old dead thread, hope this is like the other car forums I'm on and this preferred vs starting a new one...note this car is new to me and I have it ~60 days and have only put >1k miles on it. (currently 136.7K on the clock)

Sounds like I am having similar symptoms to OP but not exactly. This has happened three times to me so far, first time was shortly after driving in heavy rain, the next was no rain that day at all and the third it had rained hours before and there was no water left on the ground.

Driving or engine running-tach will drop to zero, slip and VCD off lights lit but car runs fine (plenty of power). First time it happened I had no idea what was going on so I tried "re-booting" the car (turn it off and re-start it, this is a common first step when my Mini Cooper S does something stupid) but the car would not re-start. Cranked fine, never heard the fuel pump prime and engine made no effort to start. Did some googling on the side of the road and read about the IPDM filling up with water. Pulled the winsheild cover and found some moisture in the cavity but no standing water, the drain nipple was out and laying loose in the cavity which leads me to believe a PO has already been dealing with a clogged drain. I re-installed the nipple, did some more reading and tried the key again 10 min later, car fired up and ran great rest of the way home.

Next two times it happened I was working through a very rough idle (turns out the HKS muffin filter was falling apart and piece of trash was blocking the MAF) and one time I started it, the tach dropped off and lights lit this time it re-started next turn of the key. Once I figured out the MAF issue I re-set the ECU with the key on/off method I found and took it for a drive to re-learn. When getting home parking in the driveway boom tach drops off and lights on, crank no-start. Call if for the evening, grab a beer and go watch Archer....re-starts fine this morning. Only code I pulled was P0300 (random misfire) which makes sense because it ran like poo before the ECU re-learned then seemed to be back to full power after a couple miles.

I think I am dealing with corrosion inside the IPDM. Last week I was looking into a "no dash light" issue when I did some reading and found the 10 amp fuse in the IPDM was prone to blowing. So I pulled the covers and pulled the fuse, the fuse wasn't blown but there was visible corrosion around the contacts (nice and shiny lines where the actual contacts where though) I re-installed the fuse and still no dash lights...then I checked the dimmer by the trunk release and somehow my dumbness had turned the dash lights all the way down, turned them back and that fixed the problem but the corrosion was worrying! Now I have had the no tach/ lights on issue twice since then...

I'm not a fan of guess and check....Is there anything else I should be testing before tearing into the IPDM? Any relays that can cause these symptoms (i'm guessing not or think cleric670 would have brought it up). What is the interchange on the IPDM? Will unit's from 4 doors work in our coupes??

Thanks in advance and happy motoring everyone!

The part I'm worried about is the tach signal is sent over CAN from the ECM which usually means it's not getting the signal from the crank sensor, however without the crank sensor input the engine wouldn't be running.

I think you have two separate issues, first being either a failing instrument cluster, next time you lose the tach stop the vehicle, put the cluster is diagnostic mode (FSM under section DI - driver information) and see if the tach needle moves in diagnostic mode

Secondly I think your engine stalling is the IPDM, disconnect it, take a few good pictures and COMPLETELY disassemble it then out everything in a bag of rice to absorb condensation for 12-24 hours just like you would do for a cell phone that was submerged. When you reassemble everything use a VERY light coat of electrical anti-oxidation grease on all the spade connectors on each fuse/relay/harness/etc and plug them in, pull them out, rinse/repeat 5-10 times for EVERY individual component including the main harness.

Clean the battery terminals up and make sure they are tight and cannot be moved once clamped to the battery.

Good info cleric670!

Yeah I first thought crank sensor when it first happened (I've been a mechanic long enough to know they do weird stuff when dying) so the day after it happened the first time I put the car in the air with the engine running and unplugged...it died like I turned the key off, no cough no sputter just dead...visual on all of the wiring and inside connector came back clean. I will try and reproduce the issue in the driveway again and try the self test!

Any thoughts or feedback on sedan IPDM vs coupe IPDM? Found one cheap enough on eBay I'm willing to buy it so I can bench clean and still have the car all together.

Battery terminals were loose when I got the car, I've got them tight now as well as putting the hold down back in place...PO was not that much of car guy