1999 VT Commodore Tranny Issue

[ryalls]

Hi All,

I have an issue with my 1999 VT Acclaim 3.9L V6 295000 on the clock. The problem exists only after the tranny oil warms up and I lose O/D(4th) Gear and don't get it back until i turn the car off and start it again. Everything feels and sounds like it's working as it should apart from this.

Tranny was serviced within the last year, new fluid etc.

I have had a good read through the forum and I see this has happened to other people but there doesn't seem to be any definitive answers.

I'm keen to tackle this issue myself but would like some helping to identify the problem first. I'm a mechanical fitter so although a bit dumb I know how to use a spanner ;p

I'd be greatful for any help or advice.

Many thanks
Dan

 

[Turtl3]

Could be something simple like the lockup/od solenoid, definately sounds electrical as turning the car on and off fixes it. Ur not using the power button function r u? im pretty sure the power setting eliminates the o/d function (4th). But i could be mistaken and someone will correct me.

 

[Jxfwsf]

First step: https://forums.justcommodores.com.au/threads/checking-error-codes-vt-vx.23665
I'm taking a stab at TPS or VSS.

 

[ryalls]

nah not using the Power button.
How could TPS cause this?
What is VSS?

Has anyone had this issue and fixed it correctly?

Cheers

 

[Turtl3]

Tps can cause it by making it think there is too much load on the engine with the given throttle position for the gear it is in, so it kicks it back a gear.

Vss is vehicle speed sensor

 

[ryalls]

OK yeah I can see how that could work.
Would that only happen in O/D (4th gear) though? all other gears seem to change fine.

 

[ryalls]

Just a bit of an update with more detail about the problem.

- I'll be driving along on a perfectly flat bit of road with no change to throttle position when the car will chop down to 3rd, and never go back into O/D (4th gear) until car is turned off and started again.

- Only happens once the transmission and engine are up to temperature (after about 20km from cold start), everything works perfectly until transmission and engine are up to temperature.

- If I turn the car off and then start it again when car is up to temperature the O/D (4th gear) will work for a short time maybe 1-2km.

- All other gears seem to work as they should.

- When it happened today, a few seconds before it chopped down to 3rd i noticed the revs were very slowly increasing with no change in speed (is something slipping?)

Still not quite sure where to focus my attention, any experts out there?

 

[EYY]

The torque converter clutch will only engage when the trans is up to temperature. If it's engaging immediately after a cold start, there's something wrong. Mine usually takes around 4km of highway driving before it locks up. It could be a problem with the temp switch, but as suggested above the tps can make the transmission do some strange things.

 

[Jxfwsf]

What fault codes are showing up?

It's not going to be anything mechanical in the trans, otherwise there'd be issues in 2nd or 3rd as well.

 

[Turtl3]

Definately sounds eclectrical...tps or vss as already mentioned...if not, one of the other sensors/solenoids in the box