I have a 2003 Maxima SE with 141k miles on it. Today I went to drive
up to the gas station and my car lost all throttle response on the road.
The engine was still running and I was still in drive, but it would just
hover at like 400rpms. When I pushed the gas the car took the throttle
for a second, lurched forward, and then went back to 400rpms and didn't
recieve input from the throttle. It does this about every 5-10 seconds. Also, the battery light and brake light were
flashing on and off together, sometimes staying on for about 10 seconds.
I managed to limp the car back home but the battery and brake lights had
gone out and the ABS light had replaced them (Not blnking). That is what
it does, I've checked the battery with a multimeter. With the car on it holds
14.08 volts steadily, which rules out the alternator (in my opinion i could be
wrong). I used my OBD2 tool and the engine throws a gear 1 incorrect ratio
code (P0731). It will randomly work normally for about 20 seconds then the
issues start right back up. I'm out of ideas and would like to see if you all have any.

THANKS and I'm so sorry for the length of the post, I'm rather upset right now.

 

When is the last time you changed the transmission fluid?

 

Battery and brake is alternator. It can cause it to go into fail safe mode, but that's not 400 rpms, so that's odd. TCM will freak out over incorrect voltage, so that could definitely have caused the transmission code.

If it's intermittent, then it will be harder to diagnose, but brake/batt is a dead giveaway. Alternator can overvolt, too, so don't assume batt has to die or low voltage be shown. The lights flashing leads me to believe it was overvolting and freaking out the computers.
A wonky VRM can overvolt whenever it feels like (seen it first hand).

I would just replace the alternator, but not from autozone, and don't be surprised if you get a bad one out of the box. I've had good luck with the ones from Advance, though (several with no issue).

 

Check the power cable, also. The connections on the alternator, grounds and battery. Intermittent kind of seems like there's a loose connection somewhere. The same thing happened to my BMW E36, and after hunting all over the place for the issue, that was it.

 

UPDATE!

So I had it towed to a transmission shop because all of the 3 lights (ABS, Battery, Brake) were now off and the check engine light had replaced them with a confirmed p0731(bad first gear ratio). Turns out that the tranny was toast, and it's a $1650 repair. They said first and second gear were toast and metal was all in the fluid. But they did tell me that the car outside of that was in excellent shape (Which i had already known because it's a Maxima!) and that fixing it would be much better than buying a new vehicle. So thank you everyone for the responses!

 

That's pretty bizarre.

 

Definitely alternator. I just had the EXACT same symptoms in my '01 Forester last month. If your battery is reading 14 volts or above, it doesn't mean the charging system is working correctly. The terminal on the alternator is either corroded, or the wire near the ring terminal is charred from the heat and could break off any minute, because your voltage regulator is shot. If the battery were reading any lower than 14 volts when the car is running, then the internal diodes probably failed. New battery AND alternator. Usually regulators cost the same as an aftermarket replacement whole alternator unit if it is internal.

 

And since I forgot...get a second inspection/opinion.

I've seen shops replace a transmission b/c maf sensor was bad. Of course they're happy to charge all that cash for work whether it needs it or not.

 

That diagnosis does seem sort of strange... I would think an event would lead up to that point, or you would hear some bad noises before completely being immobile. Also, some metal shavings in the fluid can be attributed to normal wear and tear. I'm with the others here - I think the issue is elsewhere.

 

Here's what happened to the alternator wire on my Subaru, to put things into perspective. *(Contains strong imagery, viewer discretion advised)

 

I had my 02 Max go into limp mode when the alternator was putting out 18+ volts. Car would start and idle, but no response from accelerator pedal. Car would die when put into "D". No SES light, but alternator and brake lights were showing. Replaced alternator and everything returned to normal.