Automatic gearbox issue

[pmdk]

Hello,

I have an issue with my automatic gear box.

Very often, when I start the engine, my gear selection blinks on a dash board - all four gears (P, R, N, D) are blinking simultaneously. Although I can select 'drive' and drive (it will still blink) but while accelerating it feels slightly jerky. When I select 'rear drive' acceleration pedal doesn't work, there is only default acceleration when you release break pedal, the car moves slowly.

And the most important part: when the gear selection blinks, the acceleration might not work at some point while I'm driving. It can happen in 5 km or in 200 meters from the beginning of driving. So the car slows down until it stops. After complete stop I can accelerate again and it works for some time.

But if I start engine and the gear selection doesn't blink, everything is fine. The car acts normal! Except, on rare occasions 'rear gear' acts exactly the same as mentioned before.

The weird thing is, when I start engine after the car was idle for a long time, the possibility of the error is low. When I stop driving, turn off engine and turn it on in 10-20 minutes it has this error in 8 cases of 10.

I went to mechanic, he made a simple computer test and the system said that there is a problem with gearbox unit. He claims the system switches to a safe mode, that's why the gear box selection blinks. He told me I have to change the complete unit and it will cost me around $1800.

So i have a question, is the only solution to fix this error by changing the gearbox unit?

 

[ScottyP45]

The auto gearbox has its own ECU (computer), it does sound like its screwy, if replacing it works then fine, but id want some guarantee if it doesnt fix it then you dont pay.

It could be line pressure, faulty shift valves, damaged torque convertor, pinking safe mode, lots of things.

BUT he may be right that the auto box ecu is faulty, strange behaviour.

If it is, then of course you have to replace it, its not repaireable by a garage.

 

[pmdk]

The auto gearbox has its own ECU (computer), it does sound like its screwy, if replacing it works then fine, but id want some guarantee if it doesnt fix it then you dont pay.

It could be line pressure, faulty shift valves, damaged torque convertor, pinking safe mode, lots of things.

BUT he may be right that the auto box ecu is faulty, strange behaviour.

If it is, then of course you have to replace it, its not repaireable by a garage.

Yes, I'm worring if they give me some kind of guarantee for the gearbox ECU. Thank you for advice, evilscotsman!

 

[ScottyP45]

no probs mate, I have had bother with an auto box in a MR2 turbo when it didnt like UK fuel (it wanted Jap 100 RON fuel LOL) and because of pinking it would pull away in 2nd like safe mode, change to 3rd and stay there, no top gear, it was a pain. Wasn't a box or ecu fault tho, was just the main ecu not liking pinking (which is admittedly bad for the engine) - got the timing adjusted, bingo, like new.

Another motor (ford auto) had low ATF (auto box oil) and it was sluggish and slow, gutless. Topped up the ATF, working fine.

Insist that they guarantee the repair and that if the ECU doesn't fix the problem then they take it back, cos they will buy it from a breaker or ebay anyway, you know it.

I hope you get it fixed, if all else fails find an auto transmission specialist in your manor and get them to give you an appraisal.

 

[ScottyP45]

I had a google and found this:

http://townhall-talk.edmunds.com/direct/view/.eeca719/1478

It seems someone else had the same problem and it was an internal gearbox hydraulic part failure, not the ECU! They don't say what, probably the valve block at the bottom, or a solenoid on the box. Most likely and not expensive if its an actuator or solenoid.

I would not change the ecu first, thats just shot-gunning and probably won't make any difference. There is no logical fault-finding reason or evidence to suggest that the ecu is at fault.

I suspect a hydraulic actuator or solenoid, followed by a faulty valve block (heck i would now put money on that - OR - a blocked filter - causing low line pressure.)

Get it VAG COM'd and see if you get a DTC code from the auto box ecu, it knows whats going on in there. I bet it says something like "low primary line pressure, sensor1 implausible signal or open circuit"

or some such bumf.

 

[pmdk]

Evilscotsman, thank you very much for your help!

I will definitely ask all things you pointed.

If "get it VAG COM'd" means computer test by a small remote device then yes, he did it and the code said something like 'blah blah... sensor' or not sensor... it was some kind of system failure. I don't actually remember. But after that code message the mechanic suggested to change the compele unit. I reasked but he was pretty sure about that.

 

[ScottyP45]

VAG com is an independent VAG diagnosis tool, run on a laptop and is very indepth.

A hand held scanner or universal OBD scanner won't be so specific on a fault description, and will only read fault codes or readiness value, not able to query specific control modules like vag com can.

Ask on here if anyone local to you has vag com and can run it over the car specifically the autobox module, and you'll get a much clearer picture of whats going on, or go to an automatic transmission specialist for an opinion?

I think your mechanic is lost on what to do next and may cost you more in the long run trying different "fixes" that don't work. No disrespect intended, but I am from an automotive electronics manufacturing background, and these things are waaaaay beyond the comprehension of a lot of mechanics simply because they are in a different and complicated field to normal mechanical engineering. Its an automotive electronics engineer you need nowadays, as well as a mechanic for the mechanical stuff.

You need to know what the specific error reported is before you can go any further, keep us posted and we'll see if we can get this resolved for you tho! Thats what forums are for

I have vag com but im in Fife, Scotland. If you are near by then no problem to scan it for you, otherwise someone else on here can maybe do it in your area?

 

[ScottyP45]

I just thought....you have had the ATF fluid level checked and topped up to the right level first haven't you?

If not, the problems might be low fluid in the autobox and when its hot the low fluid level is causing an error.

In an autobox, the drive coupling is purely liquid sloshing between two unconnected turbines, when theres enough fluid present then the engine turbine can turn the gearbox turbine by whirling the liquid, which in turn rotates the other turbine, this is called the torque convertor. If the fluid is low, the TC will slip and overheat when trying to drive, that may be all thats wrong with it. The fluid "foams" in the TC chamber if its low and the pressure drops like a stone to the valves and actuators, causing failure to change gear, slipping into "neutral" inside etc etc

 

[pmdk]

Evilscotsman, thank you for the fluid tip!!! I will ask them to check it for sure.

The mechanic is at Al Naboodah Automobiles - the official dealer of Audi, VW and Porsche in Dubai. This is the best place to get service for Audi's. I don't like Dubai service in general, it's poor

 

[ScottyP45]

Ah, didnt realise you were in the A.E. - yeah I would check that first but I suppose any audi dealer worth a pinch of salt would check that too....but you never know