On my 1992 Q is ailing, I get 3rd, reverse and park, generally. I'd like to upgrade to ATC that starts forward in first. Can anyone say the year models involved? Does anyone have an unwanted ATC?

Thanks.

The "correct" 1st gear start TCU for your car would come from a 1993 Q45. That's the only year that had a transmission identical to yours in terms of gearing, and came with 1st gear start. It's part number will end with 64U20 or 64U75(rare). You can search for one at www.car-part.com or check out our classified section here. Many members have had good experiences with the 94-95 TCU as well. Those years were 1st gear start, but had transmissions with different gear ratios. For some reason, I remember that the '96 won't work - but I may be confusing that with the ECU. Either way, they're rare, so it's probably not a problem.

With all of that said, I doubt your problem is a bad TCU. Anyway, the basic run-down of transmissions is that the 90-93 had the same transmission, but the 93 came with a different transmission control unit that started the transmission in 1st instead of 2nd gear. 94-96 had transmissions with slightly different gearing, that started in 1st gear, but should be fairly compatible with your 92. 96 might work, but I'm thinking the transmission controller may not be compatible with your car... Clear as mud, right?

Oh, good to know. I've had this difficulty before, it was the TCU:

Drake57 wrote: ↑

Mon Feb 22, 2016 8:32 pm

It failed the AT CHECK in diagnostics mode, which points to inhibit switch, range switch, kickdown switch, idle switch, or TCU. Swapping the TCU from 1992 parts car fixed it - after TCU swap it still fails AT CHECK, but shifts normally now. Not too long ago I was having odd problems like torque converter lock at unwanted times, when crawling in traffic, or backing out of driveway.

Chart on page AT-30 of FSM is telling:
Gear position 1, shift solenoid A ON ; shift solenoid B ON
Gear position 2, shift solenoid A OFF; shift solenoid B ON
Gear position 3, shift solenoid A OFF; shift solenoid B OFF <<<<------- what happens if control system fails
Gear position 4, shift solenoid A ON ; shift solenoid B OFF

So as Jay correctly points out, 3rd is the limp home fail safe - makes sense, it will pull from stop, and run down the highway right smart(ly).

Problem is worse right after starting, I think my alternator is sketchy, that's one of the next things on my list.

The AT Check verdict can be a lot of things, including the transmission not being warmed up properly. If I remember correctly, there's a code for low voltage or battery disconnected though...

Either way, if your alternator is sketchy, I'd definitely replace that... low voltage does all kinds of weird stuff.

After replacing the alternator, TCU selects proper gear quite nicely, though in two days driving, I've had two instances of torque converter lock at the wrong time (backing up, or crawling). Unwanted lock has been going on intermittently for some time, usually right after starting. I found a 1993 TCU for reasonable price at the link above, I hope for proper selection and first gear start when it's installed.

I doubt the new controller will improve gear selection, or T/C lockup behavior, but you'll certainly get first gear start. Do you have any fluid maintenance history on the transmission? Is the fluid level correct?

Opinions differ, but if you continue to have issues, I'd address any fluid starvation issues by replacing the filter/screen assembly in the transmission. Especially if you notice any buzzing or howling noises from the transmission after warm up. They all make some pump noise when cold. You could be conservative in your approach, and just do a pan drop, filter replacement, and top off - or more aggressive with a chemical cleaner followed by a full mechanical fluid exchange. If your transmission is being held together by varnish, a good cleaning and fluid swap could make things worse faster - but you were probably already in "may-pop" territory with the transmission anyway.

First gear start TCU is really nice, gear selection works no problem. Ailing TCU has nasty brown goo at base of electrolytic caps, which is lifting etch in the area. Car drives quite well now, with exception of one unwanted lock this morning on drive to work.

I've changed fluid several times, it looks fine, pan strainer has 15k miles on it. I replaced OEM inline filter with spin on PH3600. I may restore OEM inline filter, to see if that makes any difference.

PS I have not found a replacement inline filter, does anyone have a source or URL? Thanks.

That's good news!

Just a thought.. if the inline filter replacement is more restrictive than the OEM one, could that be throwing off your line pressure and causing weird shifts and t/c behavior?

So I went back and looked at my stash of tsbs, and I see where the 91's and some 92's had a voluntary service campaign for transmission service that included a transmission filter. The part number for the filter was 15208-60U05. Unfortunately, that part number doesn't show up anywhere in a google search, or on Nissan's part site. I'm assuming they're non-stock...

I think at this point, if I were trying to make sure the aftermarket filter that you're using isn't causing a restriction or messing with the line pressure, I'd just loop the two lines together and bypass the filter completely to see if anything changes.

Thanks for checking. Both my 1990 and 1992 have inline filters mounting at lower right of radiator. I didn't realize that filters were not standard. Easy enough to take out of circuit.