been chasing a gearbox issue....

for quite some time i've been getting an occasional gearbox 'glitch'.....

every now and then, it decided to move the shift points of the gearbox up, and not be completely happy, til the car was switched off and restarted.... if it happened an off/restart cycle meant the gearbox continued as if nothing had happened! no 'down time' needed, instant restart cured it.. def hints at electrical, rather than mechanical/hydraulic...

connecting the test point to get the blinky/flash dash indicators showed nothing.....

as i had another spare gearbox ecu (actually got 2 spare!) I swapped that in, but it eventually showed the same issue! hmm not that then!

i was going to ask on here or Prime, but as the usual advice is 'put in a manual' or 'it's not a proper NSX', i didn't bother!

eventually i did it again, and this time i thought to check the diagnostics with the engine still running... sure enough we have a fault code! hurrah! 3 lovely flashes!

this points to the gearbox ecu losing the throttle position signal (permanently or momentarily makes no difference, once it's lost, it defaults to lost until it's reset!)

this tallies up with what i see at the fault condition, the computer moves up the shift points as it doesn't know what the throttle level is, and loses kick-down and torque converter lockup!

so now i know it's the red/yellow wire, i checked as per the manual, levels where expected,changing with the throttle position, disappearing when the throttle pot is disconnected so i know i have the right wire......

connections checked and cycled, trying to replicate any loose connection, alas no :(

on the way to goodwood we had to brake on a particularly rough surface at some traffic lights.. after that the gearbox was not happy... again 3 flashes in the OBD test condition.....

moving away from the ecu, tracing the wiring loom, i find the connectors between the engine loom, and the 'floor' loom.... mounted on a weak mount and in fresh air behind the drivers seat.... hmmm that could be subject to vibration.... so the connectors oiled and cycled a few times, and then supported with some foam.....

fingers crossed!

https://farm1.staticflickr.com/914/4...c2dde8bd_c.jpgIMG_20180715_115421 by jon sutherland, on Flickr

Very impressive diagnosis and hopefully rectification there Jonathan, your problem solving is like rocket science compared to my recent battery problems.
I hope you've cured it.

What did you think of FOS this year???

fingers crossed its sorted, it's the first time i've fiddled in that area, when various other investigations/swaps/changes had had no effect, so promising! just got to wait and see, the problem with intermittent faults!

i'll start a FOS thread with some pix!!!

So, it's still ongoing, it was ok for 2 weeks then returned, so another cycle of the connections and all was well for a few days, then the same again....

So next step was to put a jumper wire between the TCS computer and the gearbox controller.... this worked briefly, but didnt cure it.... soo bypassing all the connectors, I linked the wire coming into the cabin and the link wire i'd added between the computers..... Hmm still occasionally going into fault mode....

So... What is actually going on? I've tried a different controller and get the same error.... Back to first principles... Start at the top... Is it the throttle position sensor? So unplug it and drive off... Instantly I get engine management light, then TCS, while the gearbox is going into its fault state.... Right so the sensor error trips all 3 computers, but my normal fault is JUST the autobox controller... That narrows it down to just the connector to the computer and it's associated 3inches of wire (before the bypass link.... ) all the other in cabin connectors are bypassed and we know the signal is good at the TCS computer... Think we're getting close!!!!

Quote:

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Originally Posted by britlude

on the way to goodwood we had to brake on a particularly rough surface at some traffic lights.. after that the gearbox was not happy... again 3 flashes in the OBD test condition.....

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The "rough surface" caught me here. It looks likes the intermittent error is pronounced by vibration. Maybe you'll find a way to monitor the voltage signal of the throttle position signal while driving.

right, to recap.... the gearbox has been having the occasional glitch for ages, and finally set about tracing it!

here's the basic wiring diagram... engine, sensor, and 3 computers connected to the throttle pot sensor
https://farm5.staticflickr.com/4866/...28df972c_c.jpgIMG_20181105_103303 by jon sutherland, on Flickr

the first mod was to add a link between tcs and autobox controller....
https://farm5.staticflickr.com/4839/...1c9e44ef_c.jpgIMG_20181105_103426 by jon sutherland, on Flickr

worked for about a week, but still played up, so take a feed upstream of the suspect connectors, eliminating them to the autobox computer...
https://farm5.staticflickr.com/4803/...3ec6627b_c.jpgIMG_20181105_103500 by jon sutherland, on Flickr

again worked for a while but then showed itself again...... so next step was to eliminate the engine loom, unsure whether the tcs and engine ecu would see the throttle signal momentary glitch, like the autobox did.... they didn't show error messages, but was that because they weren't required at the time so the computers ignored them??...

so, i needed a throttle sensor connecter like this....
https://farm5.staticflickr.com/4894/...548143ca_c.jpgIMG_20181017_161532 by jon sutherland, on Flickr

fortunately the connector is used on many Honda vehicles,, and a motorbike one was sourced!!! and added to a cable...
https://farm5.staticflickr.com/4881/...55e150bb_c.jpgIMG_20181019_143738 by jon sutherland, on Flickr

and this was wired into the loom, feeding in to my new wires, and tapping into the logic level voltage commoning block.....
https://farm5.staticflickr.com/4825/...cd726327_c.jpgIMG_20181105_103545 by jon sutherland, on Flickr

so now the entire throttle pot wiring was bypassed into the car and to the autobox computer...... all ok

then it wasn't!!! so the only 'old' wiring to the autobox computer was literally 2 1/2 inches long!!! everything else had been eliminated.....

just to be awkward i couldn't find any of the loom connector plugs, and couldn't find the supplier i'd used to get the abs loom connectors.... second hand pigtails were available in america but had the associated lead time.... but i did eventually find an ecu adaptor....
https://farm5.staticflickr.com/4810/...03e931d4_c.jpgs-l1600 by jon sutherland, on Flickr

ok, i got more than i needed, but it did give me a chance to establish the connector retaining method!!! so another wire was added.....
https://farm5.staticflickr.com/4889/...a5f6ffed_c.jpgIMG_20181105_103609 by jon sutherland, on Flickr

when i tested the suspect wiring connector in the plug it seemed 'looser' on the test pin than the other connections, so might be onto something

now, touch wood, it's been behaving long enough to have eliminated the problem (sods law might kick in now i've posted this!) and i can start removing redundant links that i had added..... starting with reinstating the original engine loom.....

fingers crossed!

Thanks for leading us auto transmission owners through these complexities.

engine bay bypass wiring disconnected and original reinstated...... all ok so far, time will tell!!

Fingers crossed. Jonathan.

Full marks for tenacity!

Hi, Jonathan.
Very interesting.

Did you feel the looseness with the female terminal at the mating connector of the AT controller?

On few occasions, I found the female terminal broken inside the connector due to moisture but not the vibration.
So, if it happened at the mating connector of the AT controller that is fully secured to the firewall, that will be the first case hearing this type of failure mode on mainly street driven NSX.

With the vibration, for example the connectors inside the race eng dyno, even with the use of the MIL spec connectors with gold plated contacts/terminals, if they were not secured, the contacts could start showing the black fretting oxidation within 12 months.

Most of the times on our NSX, the female terminals were damaged due to the moisture starting the patina corrosion followed by the spring loaded section breakage.
Already happened at the connectors behind the boot carpet, the lock/unlock sw at the door card, ABS solenoid connector (despite being WPC type), etc.

Interested in hearing the long term feedback.


Kaz

hi Kaz,

yes the terminal in the AT mating connector felt loose compare to the ones beside it, felt like a spring had gone soft and didn't want to grip on a test pin.

touch wood, it's all still behaving as it should, and it's only done that since i replaced the actual crimped terminal in the mating connector.

the fault, as far as i could determine, was only caused when braking and going over a bump/manhole cover in the road... i learned where the fault was likely to occur on my work commute.... and learnt to avoid them.. not i'm hunting them out, to confirm the cure..... lol!

Thank you Jonathan for the info.
Don't have access to AT controller but probably using the hybrid connector from AMP (now TE), Sumitomo, JAE, Yazaki or something else and for sensor signal, probably 040 terminal in use.

Never heard of similar issue on connectors at the firewall but just like the Main Relay, long term vibration could be part of the cause.
I think I have spare terminals so one day, I better go through the terminals at the mating connectors of the ECU as the car has already covered nearly 160K miles now.


Kaz

hmmmm. engine end of the throttle pot wiring returned to stock, and 3 days later the problem returned..... so back to the piggy back wiring i fitted.. surely i couldn't have 2 faults on one wire??? we shall see if it happens again..


i HATE intermittent faults