Help! My q-45 only has high gear

[TrendsetterAuto]

Hello, I am fairly new to this forum and have been using your info a lot the last year or two since I caught this Q-45 disease. I could really use some help here, my 1990 Q has some transmission trouble.
It is a bit of a long story to lay out all the symptoms and back history, but a long story short is I limped the original trans along until one day it wouldn't shift down at all. I bought another transmission and controller from a running driving car that was hit in the side and swapped it out a few weeks ago. And what do you know I still have the same problem! only now it doesn't throw the transmission malfunction on the dipslay. I have also noticed that I don't have any reverse lights. The car starts when in park and neutral as it should. It has forward reverse and park where they should be on the selector, linkage seems to be adjusted ok. But it seems to only have high gear, it wont shift down at all, not even with 1st or second selected on the shifter. this is the same problem I had prior to swapping the transmission. I thought maybe it was the controller so I swapped that with no change, I've checked fuses and switches in shifter, could it be a ground problem or something stupidly simple like that? It almost seems like the transmission is getting no power at all except the neutral saftey switch works and allows it to start. I also would like to have a look over some wiring diagrams for the 1990 Q-45 if anyone knows where to find them? this car wasn't available in canada until 1994 so my dealer here is of very little help.
Any ideas would be helpfull
thanks

[goody90q45]

Is the check engine light (CEL) on? If so could it be in limp mode because of some other problem like TPS? Will it rev over 3000 rpm.

Moderator- can you move this thread to the Q45 forum.

[TrendsetterAuto]

I haven't had any lights come on or even the transmission malfunction warning that always came up with the last transmission, although I have only driven it the few miles to get it home then just in the driveway a few times as I try different things. I would really like to no how the shift silanoids are controlled and if a bad ground in that circuit would cause a problem like this. The last transmission never consistently shifted down as it should sometimes would sometimes not, and selecting first or second on the shifter didn't do anything either until one day it just stopped shifting down at all, even on start up it takes off in what seems to be drive if not overdrive. The new transmission is doing the same thing but the car it came from was running and driving when it got hit so I assumed it had to work better that mine, and the problem I have may not be in the transmission at all.

[nissangirl74]

I moved this here so the Q45 guys could help you out. The earliest FSM we have is the '94 so that won't do you any good. However, I'm gonna send a PM to the Q45 mod for you so we can get you some help ASAP. Hang in there and welcome to NICO!

[mcrews]

Shoot in the dark.....

I was stuck in 4th (p0720) I replaced the sensor but no go.
Ended up being a relay.

[Q451990]

to NICO!

Let's start by running the self-diagnostic for the transmission. Although there are differences in the '94 and the '90 the test procedure should be the same. You can find the self-diagnosis steps starting on page AT-41 of the factory service manual.

It's located at www.nicoclub.com/FSM/

Heath

[TrendsetterAuto]

Thanks guys, I've looked at the fsm before and got a little overwhelmed but mostly tired of running back and forth from the garage to computer,
i think i'll try download it to my iphone or something so it goes faster.
As for the relay mentioned above, would you know which one and where?
I have a spare motor and trans here so i have swapped out things like tps and knock sensors that apparently play into it somehow. but have stumbled accross the right thing yet

[elwesso]

I don't like playing the guessing game with the AT. Do the self diagnosis and see what happens. Very important that the engine is at operating temp, because it often times will not work if the AT is not warmed up.

I have heard of inhibitor switches going bad causing this issue.. Rare but I've seen it. It is clearly an electrical issue, and will likely be easy to fix because it has to be something on the car, not on the trans itself.. If the self diagnosis doesnt work, then I believe there is a nice chart in the AT section that has all the pins on the TCU and their expected values. That would probably be a great start if the self diagnosis didn't work.

If the TPS is bad enough to cause it to be in failsafe, you'd also have a CEL. TPS usually don't go bad even though many people like to blame them.



BTW with the FSM, best to just print out necessary pages and go from there.

[SteveTheTech]

I should like it is in some sort of fail sake just going off it being stuck in 3rd.

Also given the desire for these cars to rust and age, I'm betting there are a few grounds on the engine that may be corroded or missing. If the control unit was not getting power it would cause this to happen.

The TPS working but being out of adjustment would cause a shift issue especially if the closed throttle switch was out. I know the book has a test using a digital multimeter that will prove the sensors works. While you have the DMM working check power and ground.
I only have the 94+ manuals, maybe one of the other guys can let us know if the process and control units are similar.

[TrendsetterAuto]

Ok guys, thank you all very much! I had a chance to get out there tonight with my multimeter and found that I had no power to the tcu. I traced it back to a short in my backup lights that kept popping the b/u fuse. Fixed the short and got power to tcu and it works again! My kick down switch is reading out of range and it only partially works but I at least have all gears on the selector again.
Man I'm so glad it was a cheap fix!
Thanks again for the input