2003 Altima 3.5 SE: Transmission goes "neutral" during driving!

[92FLQ]

During driving the drive train is somehow disconnecting with the same effect as if the transmission has been shifted into neutral.

It hasn't of course, the shift indicator is still in "D", there is simply no power going through transmission and the car coasts to stop as if in neutral. The engine is still running fine and revs freely. Shifting down into 3 or even 2 while the car is thus coasting to a stop has no effect, still "neutral". After 3-5 minutes with the transmision in "Park" and the engine running, can shift into "D" and drive normally.

No CEL or any other indicators have lit up; there is no unusual fluid leak, bad smell, etc. Transmission fluid was good, clean and red, and up to HOT level; a flush-and-fill had no effect, as latest event occured after that service. Am going later today to get ECM read, even though no CEL. Car has 90k highway miles ( I go back and forth across Florida twice a week for jobs.)

This has happened six times in the last three weeks. Four events happened at highway speeds and two in-town. Of the highway events, two were while on cruise control and two while on the gas manually, with the most recent occurence two days ago, while driving on Alligator Alley at a sedate (for me) 75 mph (on cruise). In-town events happened while negotiating 50-mph sweeping RH turn, and one more time when moving away from a stoplight while turning left onto a surface street.

I am stumped, how does a transmission go into neutral, in effect, without being shifted there physically? Is there something that could electronically disconnect the drivetrain? (the lockup torque converter maybe? But if the lockup circuit failed wouldn't it just go back into normal mode?) Are there sensors that could be compromised somehow? Grounding bad? Suggestions, please?!!??

[92FLQ]

PROBLEM SOLVED:

After a session at the dealer, and another at a very good independent local shop, where the transmission and TCU and ECU were all checked out, nothing was found, and neither the dealer nor the independent shop were able to cause the "neutral" event to happen even though between the two they had the car for a week and 2 days.

Of course another "neutral" event happened while driving in-town two days after we gave up and I got the car back, with the same results; and then three days later, the "neutral" event happened again at highway speed (65 mph, no cruise).

After coasting to a stop as before, THIS time for some reason I decided to turn off the ignition switch ( when this happened before I had always left the ignition alone, as the engine was always still running, and after a few minutes was able to shift into drive again and go on... )

SO this time when I turned off the ignition, after a few minutes upon trying to restart the car I had a no-start situation with the typical "click-click-click-click" of a dead battery. After some very fortunate good-samaritanism ( if you are ever in Southwest Florida and need a tow, call "A Budget Towing 239-896-5008, the owner of the company pulled my car back home for free ) the next day I pulled the alternator which failed a charge-test.

Replaced alternator (which is a pretty involved job, had to remove radiator to get it in-and-out) and it has been four weeks now and no problems, no other "neutral" events.

After discussion with both dealer tech and independent mechanic, we all seem to agree that the transmission must have been going into some kind of fail-safe mode as it either lost electrical power intermittently or experienced a low-voltage situation, due to the ailing alternator.

I have had alternators go bad on other cars before, but this was a first for the symptoms being manifested in the transmission before anything else is apparent; there never was any dimming of headlights, loss of radio presets, "battery" CEL, or anything else to indicate a low-charge rate situation. Maybe these transmissions are really sensitive to voltage or amp drop or fluctuation...

I hope this maybe helps someone else with weird symptoms in the trans or elsewhere; sometimes the problem is not where it seems!

[dmxplayainc]

wow just bought an 03 altima and its doing exactly what you have described .... so the alternator it was .....would have never guessed it if it was not for your post .... thanks i will be replacing the alternator soon

[tcompton0520]

Don't be so quick to think that a new alternator solved the problem. We just replaced the alternator in our 3.5 SE 2003 Altima two weeks ago. Last night, we experienced the problem with the engine losing responsiveness to the accelerator being depressed. It seemed that the engine would give us "idle" speed but it would not respond with anything better. The card did manage to go up and down overpasses on the freeway until I was able to get to a residential district and pull over completely. I tried turning the car on and off, and going through all the gears. The engine would "rev" when the car was in neutral or park, but the engine would only respond with "idle" speed in Reverse, 3Drive, 2, and 1. Noticeably, the transmission would send out a loud "thunk" when I placed the transmission into 3D. Finally, I moved the transmission lever to 3D and experienced a smooth feel and no loud thunk. I thought, "wow, this is different", I pressed down on the accelerator and the car reacted as it should the rest of the way home, about 18 miles, mostly freeway miles. Did I mention that before the engine quit responding to the accelerator that I had floored the gas pedal when leaving a red light. After I made it to the speed I wanted, around 60 mph, I took my foot off the accelerator. When I tried to accelerate again, I received no response from the engine, except to maintain "idle" speed. I wonder if I triggered a governor, a sensor, or something else. However, not during any of this experience did any Check Engine Lights appear.

[92FLQ]

FOLLOW UP: 4 years later and the problem never reappeared, 3.5 still going strong with additional 90,000 miles on the replacement alternator.