auto trans issue with re4r03a

[riskset]

hi all,

my petrol/lpg 1990 tb42s has lost overdrive. takes gears 1 thru 4 just fine, but will sit in 4th at 90k to 100k without locking up. unfortunately we were on middle section of trip round oz, so have driven home to investigate. i had an AT service completed before we left, and fluids changed and levels checked when the problem first occurred. it was not fluid levels related.

my approach has been to check the electrics via electronic control unit first before pulling anything apart as i have never pulled down an AT unit. also thought the more specific i can be the cheaper it might be. anyway, the only odd readings i am getting are 10v on pin 17 (full throttle switch) when releasing accelerator (shud be 1v or less), 3.35v (should be 3.4 -> 4.4v) on full accelerator - nearly, but is it a meaningful shortfall?, and confirmation via PIN 22 that the lock up solenoid is getting no voltage. in particular, the fluid temp sensor is feeding voltage (although i didn't confirm all ranges).

i talked to wholesale automotive and man were they helpful. basically suggested getting the vehicle to lock up speed, then manually feeding voltage to the solenoid to check this is the only issue, then problem solve why the ECU is not sending voltage originally.

i've read with interest others issues with GQ AT's and just thought i'd contribute.

wasn't sure if this should go in electrical or drivetrain.

will update as i go, and please comment if you have any contributions.

cheers,

[NissanGQ4.2]

wasn't sure if this should go in electrical or drivetrain.

You were close, there is a category called Gearboxes ( Auto / Manual ) under engine and drivetrain. I have moved your thread there.

Sorry I'm not much for electronics :) I have recently rebuild my RE4R03A gearbox, due to loosing everything above second gear.

I wouldn't believe there is an issue with the ECU ( Engine Control Unit or the TCU ( Transmission Control Until ), it's vary rare they fail, but anything is possible.

Just a matter of elimination.

If you have being speaking with Wholesale, I would be doing what they say. I bought my rebuild kit / bits off them and besides some minor mishaps with them which were not really there fault all I can say is they know there stuff and I would highly recommend them to anyone that was having issues with there auto box

Good luck mate and keep us posted

[riskset]

thanks NissanGQ4.2

so this morning i got out and checked the voltage feed from the fluid temp sensor and it seemed fine. i then bypassed the control unit and fed battery voltage to the lock up solenoid when driving >80kph to check the solenoid was actually capable of operating. it is.
so i still have to find out what is causing the control unit to not feed the lock up solenoid, but at least i know the solenoid is not faulty.

however while i had overdrive engaged on the freeway i noticed the engine speed for 100kph was higher than usual. usually, the tachy would show around 1800rpm at 100kph in overdrive, and now is showing 2200rpm.

i'll spend some time on the full throttle switch voltage as it could be this is causing the control unit problem, but i'm not sure where to start with respect to the engine speed.

would welcome anyones thoughts.

cheers,