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?
Sure. I have no way of knowing what the last AT fluid was used in the transmission as it was over 15 years ago. At the moment it has Nulon Dex III multi-vehicle AT fluid. The transmission has these two numbers on it: 9X86152 and 51X04. I have a spare valve body I’m going to try out today, my theory is something somewhere hydraulically within the transmission isn’t getting enough pressure to turn the wheels faster than a slow crawl. When I say slow crawl the wheels don’t move in gear until the accelerator is pushed, and then still it doesn’t spin the wheels fast enough to move the car over a small hump.
Sorry, didn't read the thread, just your last post. It kinda sounds like the trans is low on fluid. Have you double checked this? Withe the engine running, you must run the shift through all gears waiting about 20 - 30 seconds in each gear. Then remove and wipe the dip stick, replace, remove and take a reading. Be aware the levels are slightly different when cold versus hot. Assuming you have the correct dip stick length and dip stick tube fitted. You could also fit a pressure sensor in the trans line. The sensor should be a 150 or 200 PSI sensor and measure the line pressure. The pressure values should be in the manual. I really don't like removing valve bodies unless the trans is out of the car.
I’m halfway through installing the new valve body now. I don’t think I specifically let it sit in each gear for 20-30 seconds, though it has warmed up and I’ve checked fluids previously. I’ll give this another go once the new valve body is installed. Something weird is up with this new valve body though… The gear selector stem on the old valve body has a cylinder on the end with a notch in it that connects up to the shifter linkage assembly, however the new valve body just has a gear selector stem with a cylinder on the end and no notch for the linkage to lock in to? Weird. Has anyone come across this before? Have a look at the pictures
Update, Ivan’s advice worked here. After fitting the modified valve body yesterday there wasn’t any improvement, only upon adding almost another 4 litres of transmission fluid this morning has the car began to run normal. I kept running it through each gear for 20-30 seconds, then would check the trans dipstick between. It sucks up a lot of fluid when it starts up, so the reading while it’s running is quite different from when it’s off. It’s at a level now where it shows full on the dipstick WHILE the car is running. Car moves around nicely now!
This happened to me at Z fest one yr. After installing the rebuilt transmission, I got to Z fest location without a problem. Went to move the car from the parking spot, which was slightly uphill, in the morning and it required quite a few revs to move. Long story short, it required more ATF and I swore when we did the trany refill we were measuring the ATF as accurately as we could but it was not good enough. When I made it back home, the fluid was dumped and refilled with fresh ATF because the old fluid would have been overheated and lost some of its properties after that saga. The tranny has worked flawlesly since. Sometimes, it can be the simplest of things.
Like ivan said earlier, there's a process to go through when filling up the Transmission with oil to ensure the correct amount is added. (The oil level can't be too much or too little, it has to be quite accurate) This needs to be adhered to strictly as per the manual, else the oil level won't be correct and the Transmission won't function correctly.
Burnt or over heated transmission fluid will smell different to fresh fluid and can often be slightly darker in color. If you suspect the fluid has been over heated, dip the fluid and compare it with fresh fluid. You can also try the white paper trick by wiping oil from your dipstick (taken after the engine has been running and fluid up to temp) onto a piece of white paper and doing the same with fresh fluid. Good fluid from the car should look like the fresh oil sample. The reason you run the transmission through each gear is to fill the clutch drum of each gear. Fluid can drain from the clutch drums when not in use. A transmission should hold enough fluid to fill the convertor and each gear's clutch with reaserve in the pan. This is why you run the shift through all the gears before checking the level. The most common cause of a transmission not picking up gears or slipping is low fluid level, next is low line pressure or faulty line pressure control. Most tranmissions will just expell excess fluid from their breather or push it up the dip stick when driven under heavy load. That doesn't mean that its ok to run with the trans over filled. Always a good idea to run the correct fluid level.
