[SOLVED] [Automatic Transmission Failsafe Mode Troubleshooting] Transmission Control Computer

Also, this vision is in my head...(original picture credit to @MrJPolito)



NOTE TO ALL: THIS PICTURE CAN BE VERY INCORRECT!! Still just sharing ideas...but I feel as if the original shifter could be utilized to get the solenoid response I want. At the end of the day, I BELIEVE the shifter position is just bridging certain wire combinations together.

 

My additional thoughts: if both your solenoids are good, but the pooter is bad, that might mimic "both solenoids malfunctioning", because I'm ASSUMING that particular computer tells the solenoids what to do (ON/OFF) and when to do it (RPM pattern depending on PWR switch selection).

Thus, if you (1) have a bad pooter, and (2) have 2 good solenoids, then (1) you would only have 1st gear (while in L) and 3rd gear (while in 2 or 3), and only when you are manually actuating the tranny, (2) the PWR switch would do nothing, and (3) removing the pooter and driving would produce no difference.

 

Mr J. Does your new book talk about voltage to the transmission solenoid?

 

I have never been a fan of "miracle in a can" solutions ( pun intended ), but my experience with Daihatsus has taught me that Sea Foam is indeed a miracle. For what it is worth, you could try Seafoam Trans Tune, and see what that does.

 

That might clean up the transmission hydraulics, but won’t do anything to heal a corroded computer module.

 

@MrJPolito,

Did you happen to take a photo of the transmission ECU plug side? I'm trying to determine if there are potential substitute models with AISIN 3-speed automatics (e.g., Daihatsu Charade?).

 

So good news I got my transmission computer back from getting the capacitors replaced and it works again. The transmission shifts in drive and the pwr button light goes on and off.

 

That is awesome news. Where did you get yours done at? You can PM me if necessary.

 

It was a friend of a friend. I bought the same spec capacitors at a local electronics store.

 

That is very good news, also the pics with the specs of the caps to order. Will help many members with the same problem, good team work of all members contributing to solve the problem.

 

I need a friend of a friend!!!

 

@Ronso ,

I CERTAINLY appreciate the pics, but can you perhaps provide a few more details?

I think I see 5 total capacitor replacements? Per my labeled pic, I see that 2 & 3 are 10 mF @ 16V. Do you know what 1, 4, & 5 are?

 

@Ronso ,

Disregard...I found this from earlier:

 

I just received a backup transmission computer I ordered from Japan. It's out of a DAIHATSU Hijet atrai 1995 V-S120V. I just tried it and it shifts in drive like it should but the PWR light flashes.

 

Good info! I was considering other models as well. S120 is the 2WD van, correct? S130 would be the 4WD? I wonder if that difference has something to do with it? (I doubt it...because I wouldn't expect a different part number for the AT ECU just because you have 2WD vs 4WD.)

At this point, I plan to try the "change capacitors" approach.

 

Im not sure about the 2wd vs 4wd. I only bought it because it was 1995 Daihatsu and the same plug in. I also couldn't find anything remotely close so I figured it was worth a shot.

 

Yep, I was planning the same. That's why I appreciate you sharing your results -- because now I am focused solely on the capacitor replacement.

 

Add me to the list of successful capacitor replacements!! I'll admit, a PITA. I had lots of trouble getting the solder to adhere to the original board...and the drizzled epoxy stuff on the board made it all the more challenging. But, alas, a PWR light!

Driving impressions: WOW! Yes, I now have 3 distinct gears. It upshifts and downshifts at make-sense times. Just based on a few drives, it seems the PWR mode increases the RPMs more before shifting. The vehicle feels plenty peppy, and likely shifts faster than I ever could.

Now that I have a working automatic, I'm so glad I went with it. I'm at 6', 200#, and I fit nicely into the vehicle. But, if i had to constantly clutch and left hand shift in this little thing, I think I'd be annoyed.

 

A few tidbits of info when you decide to repair your tranny ECM (and you should!):

(1) Capacitors have polarity (+ side, - side). See diagram:



(2) The microfarad (uF) number needs to match, but I think you can get a higher voltage rating than the originals. I purchased 22uF, 50V, 105C (3 locations) and 10uF, 50V, 105C (2 locations).





(3) The tranny ECM is bolted to the front wall, behind and to the right of the speedometer cluster (while facing the speedometer cluster). I removed the cluster and had to also unbolt (but not remove) the steering column. (I was also installing a tach and a radio, so I had already committed to removing those items.) I rerouted my tranny ECM to hang below the diagnostic plug port (below the brake fluid reservoir). Now it is easily accessible, and once I confirmed it was working, I just taped the lid back on and tucked the ECM above the diagnostic port.

 

Where did you order it from? I can't find any replacements at all. My board is definitely fucked. I broke too many tiny metal pins and solder won't stick to anything that small.

Here is the automatic transmission section from the Japanese manual that I purchased if anyone is interested:

https://drive.google.com/file/d/1uJkZatE_dVh-zyeKIyTwcOcJ5lbhbhpP/view?usp=sharing

You'll need to use the Google Translate app to translate images of the PDF file into English, or copy and paste screenshots into Yandex image translator. Page 44 of the PDF is where the transmission computer stuff starts.

 

How bad is it? Since we have the same vehicle, send me yours and I can take a stab at repairing. It'll be easy for me to test because now my ECM is tucked below the dash.

 

Pretty much every single pin that arches between any of the metal pads is bent or broken off. It's because I used silicone to hold the capacitors in place, then decided to rip it off and redo the solder because it wasn't sticking correctly. It's not worth it. I've already listed the car for sale anyway. It's turning into a money pit at this point.

If anyone else does decide to do this, which I think it's totally worth it and will probably fix your problems if you're not an idiot like me, make sure you use a lot of flux paste when you're soldering. The board is very old and the solder is not going to want to stick to any of the metal without using flux paste.

 

Marked the thread as solved since it seems to be the AT computer causing the problems here, and replacing capacitors seems to fix it. If your PWR light doesn't come on when you press the switch, your computer is broken and needs new capacitors.

 

My next plan was to drill small holes in the board, larger holes in the metal backing plate, insert long-ass capacitor legs, solder a puddle into the holes, clip excess legs off bottom side, silicone the larger holes.

But, if you butchered your board in a rage of fury (I'm not judging...I almost did the same), then I agree there is little that can be done. If not butchered, feel free to send it to me and maybe I can get lucky!? Even if you are selling, your purchaser can benefit.

 

It was a mixture of rage and also silicone being a bitch to remove once it's cured lol. I don't think it's salvageable, the nubs of pins goes under the black potting compound on the board and it's too small to stick solder to. You'd have to chip off the potting compound and probably break the rest of the board.

Ronso said he'd send me his spare one to try out so I'll let you guys know how that goes.

 

Alright, so the one Ronso sent is from a Hijet Atrai S120V van, and mine is a Hijet S110P truck. His computer has an all metal housing whereas mine was plastic with a metal back. The ports are exactly the same. I plugged it straight into the harnesses already in the car. My Japanese manual says the wiring should be the same between these models. No idea why they'd have different computers.



The PWR switch works now, so the computer is working. But after driving for about five minutes the PWR light just flashes on and off constantly. I bridged the pins on the diagnostic port to check the A/T computer codes and got code 21, 23, and 25 - no connection to the No 1, No 2, or B1 transmission solenoids. So it thinks there are no solenoids plugged in. None.

I have no idea if this computer can tell it's installed into a different transmission and therefore won't work, but everything in the manual suggests that automatic transmission wiring is not different between S100-series vehicles.

I'll check the solenoid wire harness for continuity at the very least. I've never even seen a harness for the B1 solenoid, but I know where the No. 1 and 2 solenoid harness is located.

 

I feel like the highlighted portion is a clue? Since it seems a common problem (all solenoids open circuit), maybe your 4WD pin 18 is messing with your 2WD computer? I sort of expect your computer to not have a pin at 18, but if it does, try disconnecting and see if any change?

I have no idea how to resolve pins 12 and 17.

Did the vehicle drive differently? I'm expecting 'no' if it thinks all solenoids are disconnected?

 

Nope, there was no change in the way it drives when I had the new computer plugged in.

Quick update: I checked the harness for continuity between the solenoids and the transmission computer, and there appeared to be a break behind the dashboard somewhere. I completely bypassed the wires at that point and ran a new wire for each solenoid. Solenoid #2 is now detected but solenoid #1 is not. I think the pin on the harness is loose or something. Might try to shove some copper tape in there tomorrow to get the connections snug.

Also, I have no B1 solenoid. And it looks like only vehicles with a turbocharger have one, according to a wiring diagram that I was looking at earlier, so hopefully that isn't required for this transmission computer to work. Maybe there's a way to trick it into thinking it's there, but I am completely missing that pin on the wiring harness.

Edit:
Here is the wiring diagram for the transmission computer, showing wire colors:



Here is where the solenoid wires are located on the wire harness in an A/T, 4WD, S110P EF-ES Truck, with wire colors labeled:

 

If any of you are unfortunate enough to have to replace your terminal pins and wires leading to the A/T computer, I believe I've found the exact fit pin on DigiKey.

Here is the terminal pin I removed from my wire harness with one of the solenoid wires next to it:


I've annotated some of my own measurements that were made with a crappy Harbor Freight caliper. They seem pretty damn close to this model though:
https://www.digikey.com/en/products/detail/te-connectivity-amp-connectors/173716-1/744774



My new wire is 18 AWG and the range of this terminal pin is 20-22 AWG, so no idea if it'll fit, but there are a few other options out there that I might order alongside this and I'll report back how picky the wire harness is.

Note that if your solenoid wires are bad at the terminal like mine are, you probably need new terminals too so that you can replace everything up to the end of the wire where the break in the wire is probably located. My terminal pins broke when I tried to open up the crimped part covering the old wire, so I need new ones. They're very small and very hard to re-use.

For instructions on de-pinning the wire harness, check out this page for a nice cross-section of how a terminal pin is inserted into the harness: http://ae64.com/Pin_insertion_extraction.htm

I pried the white cap off of my wire harness and probably broke some plastic off in the process, because I'm a big dumb brute with no finesse, so I have no idea how you're actually supposed to get terminals out the 'correct' way. But a jewelry screwdriver is necessary to de-pin the terminals.

 

“wiring harness pin removal tool” turns up a bunch of options on Amazon.

I have a kit with 70 or 80 tools. it cost less then $25 with free shipping.

When I did the wiring changes on Hijet, a lot of the white plastic connectors were crumbling in my hand. So, they got replaced with modern automotive connectors.