Please help! my 1997 maxima is in fail-safe/limp mode. it only drives in 3rd gear even if i switch from "D" to "2" or "1". Overdrive light doesn't come on. Here's history that got me to this point:

April/May 2017:
-battery dead, so jumpstarted then replaced
-dashboard and headlights intermittently dimmed/brightened while driving
-new battery caps popped open multiple times. had battery checked, and tech said battery fine. he suspected alternator is overcharging battery

Sep 2017:
-for several months, continued to experience dashboard and headlights intermittently dim/brighten while driving
-after long highway drive, noticed strong toxic smell. Discovered battery caps popped off and battery acid was spilling causing the strong toxic smell.
-after parking for awhile, car wouldn't start. barely got car jumpstarted after many times.
-Few miles down the road driving highway speed, the dashboard lights and headlights rapidly dimmed and brightened. headlights got really bright and died (blew out). engine power fell and pulsated. Barely got off highway and got towed back home around 60 miles
-i replaced battery again and was able to drive to my mechanic. he determined bad alternator and replaced. i replaced burned out headlight bulbs.
-Airbag light was blinking. i followed online tips to clear by pushing dome light button 5 times
-i discovered overdrive wasn’t working and transmission locked in 3rd gear per owner’s manual 4-10:
“Fail-safe: When the Fail-safe operation occurs, the next time the key is turned to the “ON” position, the O/D OFF light will blink for approximately 8 seconds after coming on for 2 seconds. While the vehicle can be driven under these circumstances please note that the gears in the automatic transmission will be locked in third gear.”
-i also discovered new engine code P1605 (Automatic Transmission Communication)

Oct 2017:
-i disconnected battery for over a week hoping to clear problem, but still stuck in Fail-safe mode
-Checked fuse box on the inside drivers side and discovered IGN 7.5A A/T CONT fuse blew. i replaced fuse and turned to ON. O/D light came on dashboard for a few seconds and disappeared. The fuse blew again. replaced fuse again and same thing happened
-brought back to mechanic and he recommended seeing an electrical expert. strangely, IGN 7.5A A/T CONT no longer blowing but O/D light doesn't come on for a few seconds like before.

i'm still stuck in fail-safe/limp mode. it only drives in 3rd gear even if i switch from "D" to "2" or "1". Overdrive light doesn't come on. i believe the high voltage pulse (due to bad alternator) which caused my headlights to get really bright and blow and caused my car to die and get towed home, also caused this problem. do you think i blew my TCM? what else could be the root cause?

Welcome to NICO Club!

Sounds like a mix of issues, including voltage regulation. Likely a fuse popped before toasting any computer modules.

You should work with the FSM for your diagnoses and repair. Here's a link to that (it's actually a link to each chapter in PDF format). The FWD is the foreward chapter and will have a table of contents. You'll be in the transmission, EC and EL chapters I think.

http://www.nicoclub.com/FSM/Maxima/1997/

thanks so much for the FSM (factory service manual) link. i was reviewing the Automatic Transaxle (AT) chapter and found "fail-safe" mode on AT-8. it says if i turn my ignition to ON, the O/D OFF indicator lamp should blink for 8 seconds. for me, it's not blinking or turning on at all. as i shared previously, the O/D OFF indicator lamp turned on for a couple seconds when i switched the 7.5A A/T CONT fuse but now it doesn't turn on at all. does this imply something more serious is wrong (e.g., bad TCM)?

AT-25 says i need to erase DTC's for both ECM and A/T control unit. i've cleared DTC's with my cheap OBD2 reader, but not sure if it clears for DTC's both ECM and A/T control unit. is additional work/tool required to clear DTC's from A/T control unit?

The light blinking or not blinking has a meaning I'm pretty sure. FSM should detail what to do in such situations. I can take a look later, but today is busy with work for me.

For clearing the ATM codes, I'm not sure. I also only have an OBD-II scanner. Pulling the negative battery cable also kills power to the computers and resets codes for the ECU. Worth a try to see if it clears ATM as well.

thx for your help and willingness to look at FSM later today.

i tried disconnecting battery for 10 days and couldn't clear P1605. i'll try again and see what happens.

Halleluiah, issue resolved! i bought a $14.99 used TCM on ebay and replaced my original one. No longer in fail-safe/limp mode. Whoohoo!

just out of curiosity, does anyone know what that small black box right above the TCM is?

it has similar dimensions as the TCM and resembles a modem.

Yay for a working transmission!!!

You can check the FSM to be sure we're looking at the same component, but I look at chapter AT at page 9 and see a BCM (Body Control Module), so it's probably that.

yes, BCM looks correct. thx centralcoaster33 for all your help. you truly exemplify a high standard for all moderators.

if anyone runs into a similar problem as what i just endured, i'm happy to try to help.

since i replaced my original TCM with a used one from ebay, i noticed my transmission shifts to higher gear at a lower rpm than my previous TCM. in addition, my speedometer periodically gets stuck at 0 mph; engine code P0600 arises and eventually P0500 arises which causes my engine light to come on. i'm still able to drive my car fine, so i've been erasing the engine light with my obdii reader and driving along my merry way.

do you think the ebay TCM is causing these issues? my original TCM was 31036 0L701, A64-000 E54. the currently installed ebay TCM is 31036 0L700, A64-000 E46. i'm wondering if my car needs the original 0L701 TCM. i can purchase it from ebay and replace it. i don't want to waste time or money if no significant difference between TCM 0L701 vs TCM 0L700.