I'm about at my wits end here. 2005 5AT, recently (last month) had the entire transmission replaced by the dealer with a re-manufactured (which, correct me if I'm wrong, is factory ensured to work correctly). This included valve body and everything. Just this last week, I had my shifter assembly replaced after my current unit started acting up.

The car drives perfectly normal in D, but it's a total crapshoot every time I start-up if I'll be able to use manual-mode or not. Even when I can, it pops into failsafe (i.e. no manual mode) at random times like after either switching to D or R/restarting the car after parking. It's also a crapshoot if restarting the car lets me use manual mode.

As far as I know, the actual wiring between components is the only thing that could be throwing a failsafe at this point, unless the transmission/shifter assembly themselves are causing issues (in which case, yay warranty! No yay for driving an hour each way).

After I got the transmission replaced, everything was working normally for a few weeks, after which problems started again. Wiring harnesses are crazy expensive new, so if warranty work doesn't fix the problem I'll have to live with it.

Any other 5AT owners have persistent problems with manual mode? Fully-automatic works 100% fine, it's just manual mode that refuses to work.

 

Sounds like an electrical issue, I would start by cleaning up the transmission grounds located at the front of the engine, top of the timing cover, 2x bolts with wire lugs grounded to the cover. Remove the bolts, clean with a brush, apply anti-oxidation great and re-bolt to the timing cover. Also clean the engine-chassis ground located on the front passenger side of the engine, it bolts with a 2 bolt lug to the chassis below the coolant reservoir, remove the single bolt from the reservoir and lift it straight up to access the chassis lug. Also clean the battery compartment jumper from negative to chassis.

Same process for all, remove bolt, clean with a wire brush, apply anti-oxidation grease available at any auto parts store or Home Depot / Lowe's, and reattach the bolt. Even a little electrical resistance can play havoc on the system and it's a known issue.

Just to confirm you did get a new Transmission Control Module yes? It's inside the transmission behind the valve body. They did fill the transmission with the correct fluid and not some random 50 gal drum of ATF? It won't run correctly without the proper fluid.

When you say "dealer" you mean a Nissan/Infiniti dealership did the work yes?

 

I've done the two upper grounds, I'll try the engine-chassis ground next. I think I tried to clean it once but the bolts refused to move. I'll give it a look tomorrow, as well as the battery jumper. Which one is the negative to chassis, just the negative cable on the battery, or somewhere else?

As for the TCM, it was an entire transmission, filled with J-Matic (got the dealer's go-ahead to put in a quart or two of Castrol Multi-Import when my cooler lines started leaking). I thought that in the 2005 and up cars the TCM was part of the valve-body?

And yes, Berglund Luxury in Roanoke. Pretty decent dealership, service manager knows his stuff about cars (he used to own a pretty built 350Z), and doesn't just try to sell customers a brand new Infiniti like the previous manager.

 

Yes the negative battery cable is the one I'm talking about, it's only about 8" long and connects to the chassis inside the battery compartment, once you remove the big plastic cover over the top of it you'll see what I'm talking about. If you have bolts that are seized and couldn't previously be removed I would DEFINITELY start there, corrosion causes problems like that and if there's any visible crud on the bolt threads then you likely have electrical resistance screwing up the system, the electrical system bolts are coated in a green colored anti-corrosion material but it does corrode eventually, hence why I strongly recommend also putting a small amount of anti-oxidation grease on everything, coat the threads, both sides of the lug, and the chassis. Just use a rag and wipe up any excess.

The TCM is "technically" part of the valve body yes since it's literally bolted to the backside of it but it is an individually replaceable component, just unbolt and replace as needed but I doubt that's your issue.

You could also make a dedicated jumper just to TEST the system, take a length of 12 AWG wire, crimp on a lug that can bolt somewhere on the transmission and run it straight to the negative battery terminal.

 

After trying for a while to remove the two bolts under the coolant tank, I belatedly realized that I could just use a 10mm hex wrench to remove them. Derp.

Anyway, brushed that ground (and the others) with a wire brush until they gleamed, sprayed on some WD-40 (best anti-corrosive agent I have right now), re-attached everything, and it's still giving me problems, getting stuck in drive again.Checked the negative ground, and it still looks practically new.

I'll try your suggesting with a dedicated jumper; I just need to take some wire, attach it to a bolt that is already a transmission ground, and run it to the negative terminal? I have some wires from the previous owner's grounding kit still laying around that would work great.

 

The connection can LOOK fine but until you actually remove it there's no way to tell without using a very sensitive digital multimeter and measuring resistance. Also you may or may not have noticed but the coolant reservoir is held down with a single bolt and lifts straight up (no need to disconnect the hose) and you can easily get to those 2 bolts underneath it.

Something else to check is the physical shifter itself, might be screwed up.

 

Did you try scanning the computer at the dealer or with an advanced OBDII? I know sometimes I get an 1815 I think and manumatic doesn't work all the time. There are some tiny switches I think in there that cause a connection and tell it to go into manual mode. I'm not exactly sure how Infiniti goes about it, but on my Audi they used magnets. I had to get a new shifter or clean the magnets for that one, I would also try getting some electrical or MAF cleaner and look in the shift where it makes contact when you switch over. It just might have some built up gunk in there and a few sprays of electrical cleaner might be all you need..

 

Yeah, the old transmission threw a P1815 for the manual-mode switch failure (had to replace the whole transmission due to an obscene amount of aluminum shavings in the pan among other things). Got a brand new shifter assembly in as well.

I'm currently testing driving without the shifter cover on; I had a Momo **** for the while and had to modify the leather boot to make it work, but even before that it was drooping a bit. I'm suspicious that when I shifted to D at certain times, the leather would press the downshift button and trigger failsafe mode (if hold down that shift button, failsafe for the tranny should activate in a few seconds and lock you out of manual mode).

Seeing as only the assembly and main wiring harness are the only non-new things pertaining to the transmission, I'm testing the easy stuff first. Plus, I kind of doubt a failing wiring harness would cause intermittent issues instead of constant.

 

Did u ever find any fix for this?

Im having the same exact MM issues youve described. Kinda hard to troubleshoot because its so random.

 

I've only had the car locking out of manual mode less than three times since I had the transmission replaced, each time seemingly randomly. I do still fairly often get a problem with the car refusing to downshift in manual mode, but I do notice that when the car is letting me do it whenever (driving aggressively in downshifting very high), it will do that indefinitely, then the next start may just refuse to downshift. I think I got my shifter assembly used, and I believe that is my current point of failure, the actual switch itself. I cleaned up every single ground, checked blue levels, and recently got a Nissan dealership transmission drain and fill as my fluid was nearing 30,000. Seeing as shifter assemblies are expensive, I'm still trying to find fixes for my current one before buying one.