Alrighty...I got a question for anyone out there that has possibly had the same problems. Let me start by saying I have a 1988 Toyota Pickup 4x4 Xtra Cab pickup, v6, auto trans (A340H) with the overdrive and Power Button option. It is in great shape, runs like a top...HOWEVER...I seem to have a nasty little bugger of a problem. During daytime driving, the trans shifts fine, no problems...But come nightime, the gremlins appear. When darkness hits, the trans starts to bugger up, stays in second (even when stopped), doesnt want to shift, etc. Lol wtf? However...the technical side of it. What truly happens is that the trans starts acting up when the headlights and/or heater blower gets turned on, which leads me to think there is a weak power wire somewhere, or possibly a weak ground? As I'm to understand, there is a Electric Trans Control Unit (for the power button and kickdown I'm guessing) and what I'm wondering is where should I start looking? I'm guessing that when theres too much of a power draw on the battery, Maybe the ETCU isnt getting enough power due to corroded power wire or ground to the unit? Any help or advice would be greatly appreciated. Thanks

 

Sounds like a solenoid may be on it's way out. Start by checking for codes.

 

Whats the process for that? I have no check engine light...and would a (shift) solenoid get weaker due to a draw on the electrical system? I'm trying to isolate the problem...and when I have time between work and more work I plan on tearing the center console out (as I've heard that the ETCU is located in front of the shifter under the console) and check the wiring...and if nothing is bad or corroded there I was thinking of tracing the wiring loom to wherever it goes (fun fun) and look for corrosion possibly outside. I had a similar corrosion/weak power supply issue with the main power wire that runs to the fuse/relay box from the battery. It was corroded and would get rather warm when all the electrical was on (lights, heater etc) and it showed like 11 volts on the volt gauge I have, soooo I replaced that wire and cleaned all the chassis and engine grounds...and low and behold the voltage stayed right at 14 volts even with everything on. So thats why I figured it might be the wiring on some part of the harness from the ECTU to wherever it goes being corroded. I will look into solenoid possibilities, but as I said the trans only acts up when theres a large draw on the electrical system (ie. daytime driving is perfectly fine, all 4 gears hold and shift smooth with no slipping). Thank you for the advice, I will keep you updated!

 

Check out the transmission diagnostics section of your FSM. Link in my signature.

 

Thank you!!! That link rocks!!! I will keep you posted! Thanks again