Hi guys! I’m struggling to get my automatic transmission to engage any gears, 1st, 2nd or Drive. Upon following the steps in the service manual I’ve been unable to get the transmission control unit to enter into diagnostics mode. I continued to follow steps and test continuity on the pins from the TCU to ground, which seemed fine, though upon linking pins 3 and 4 I couldn’t get any transmission indicator lamps to light up either. My current thinking is I need to try another TCU or there’s something mechanically wrong in the transmission. I do have another valve body I could switch out, but don’t have a spare TCU, though it’d be great if I didn’t have to go down these routes. Does anyone have any other ideas I could try or experience they’d like to share around getting the TCU into diagnostics mode? Also, the only 3 lights I get are “Power”, “O/D Off” and “Hold” - in that order. Can toggle these on and off, is the “Power” one also the one that blinks during diagnostics on the JDM model 2+2 1989 auto? At a bit of a dead end at the moment
The OEM ATCU can go bad after 30 years of use and transmit false signals. I would try another ATCU if you can first.
I can remember reading that the trans fluid level needs to be spot on. And checked at the right temperature.. easy to do before you embark on any swap outs.
Yep. But given that the OP can't get any response from the ATCU in diagnostic mode I'd be starting with the basics. Do a Break & Make on the connectors of the ATCU & the ECCU. As in, disconnect then reconnect them. It only takes one of those hundred or so connectors to get a bit scabby or corroded, to cause grief. Ruuksine, have you tried that yet? As in lifting back the carpet in the front side passenger footwell where the control modules are. Sometimes we find signs of liquid leakage & corrosion when we lift the carpet. Maybe from coolant, maybe just rainwater from bad targa seals. Don't be looking for obvious / traditional signs of red rust. Remove the connectors and look for white powdery deposits on all connectors.
Well it worked for me, I had a transmission shifting issue on my trans that existed for 10 years or so where my auto would not shift from 1st gear into second and I could even hit the rev limiter and it still wouldn't change. I spent $600+ to buy a laptop and consult software to run diagnostics telling me I had multiple codes including a tps signal error and a turbine error. After I serviced the trans myself with new filter and fluid it blew. So I got another transmission installed only to have exact same shifting issue occuring on the new trans. Saw a forum post on here about a member who rebuilt an auto trans and mentioned the issues with false signals on the ATCU and so I first purchase the ATCU from the same owner who I brought the trans from which still did not fix my issue. So then I brought a tt ATCU from Europe and guess what, the transmission has not had any problems shifting since then. It's not a silver bullet for the original poster by any means but it might help him eliminate his issue it may not.
Update on this, thanks for your perspectives so far. So I went down the route AdamZX suggested and got a hold of a second hand ATCU. Since swapping over the ATCU we've been able to get the rear wheels to 'crawl' enough to move the car forward and reverse as well, however, it seems like it's not getting very much power through the transmission as it won't go any faster than a weak crawl. Yeah I've had a look at the connectors on the ATCU and ECU too, nothing looks amiss there as well as doing some voltage and resistance checking related to transmission solenoids.
Can i ask if youve changed the fluid of late? and if so which fluid? If anything is used apart form whats been used all its life the box will slip and cause loss of power throughput. Had this on one of the zeds we had, used a fluid that was "specified" by the manufacturer as an equivalent and needless to say it would leave us stranded driving through intersections so it was quickly dropped and the cheap equivalent put back in and boom come good. That same trans then later in years was sold to a aus300 member and they had issues with selecting drives, i had to send them the atcu that was from our car as it appeared to have been a "matched" modified atcu to suit the valvebody. Good ol JDM mods before the car was imported. Came good with the right ATCU with the box in the end. Can you give us more of a background as to the box and gear you have?
