c5 v6 (2001), 4hp20, harsh downshifting

[koelner]

hello,

the auto-box on my car has a problem while downshifting: during braking or driving in coast the transmission jerks while downshifting (mostly just before the car comes to a stop). after resetting the auto-adaptives (via lexia) it seems to work smoothly as expected... but the problem returns after 100-200 miles. any ideas?

thx!
greetings from germany ... and sorry for my bad english

[GiveMeABreak]

Welcome to the Forum, nothing wrong with your English
When did you last change the fluid? (http://www.opieoils.co.uk/p-69401-mobil ... fluid.aspx)

[koelner]

When did you last change the fluid? (http://www.opieoils.co.uk/p-69401-mobil ... fluid.aspx)

some four months ago, while checking the oil level ... i used: http://www.ravenol.de/en/products/usage ... fluid.html

[xantia_v6]

Is it just the 2->1 downshift while coasting that is the problem? That was quite a common issue on Xantia V6s with the 4HP20.
In case you have not seen them, there is some betime reading material here:

No dice with the Xm manual but I did find theselinks;

# [PDF]
TECHNICAL TRAINING ZF 4HP20 AUTOMATIC TRANSMISSION
File Format: PDF/Adobe Acrobat
http://www.matrasport.dk/Cars/Espace/va ... aining.pdf -

ZF 4HP20
File Format: PDF/Adobe Acrobat
http://www.matrasport.dk/Cars/Espace/va ... _4HP20.pdf

Andrew

If I remember correctly, at the 2->1 downshift there are 2 electrovalves which change state at the same time, and if the hydraulic actions downstream are slightly out of sequence, then the harsh downshift occurs.

With these transmissions there is always the possibility that any long-term change in behaviour is a sign that the oil filter is becoming clogged, reducing the line pressure, which eventually causes a major failure of the transmission.

[koelner]

thx for the pdfs! the jerk occurs on different gears ... mostly while shifting 3 --> 2, but sometimes also on 2 --> 1. i suspect the ECU switches too late, if i use the manual mode (tiptronic) there's no jerk or harsh shifting at all. however I fail to understand why the problem disappears for a short time after resetting the ECU.

[xantia_v6]

I fail to understand why the problem disappears for a short time after resetting the ECU.

The transmission has an auto-adaptive function that is designed to keep the performance constant and the changes smooth, compensating for wear in the clutches during the life of the transmission.

The ECU monitors each gear change, and after measuring the clutch slip each time it fractionally adjusts a table of parameters for controlling the electro-valves in the transmission. When you reset the transmission, these tables are all set back to default values.

There may be a condition on the transmission (maybe normal wear, maybe a blocked filter, maybe some other fault) that causes the learning algorithm to go a bit wrong. It can also happen that the learned value is correct for a typical change, but something is causing the transmission to have a slightly random response, so some changes are too soft and others too harsh.

I had a Xantia V6 that had transmission parameters that seemed to be continually changing, it would drive perfectly for about 100 miles, then the changes would all get sloppy for about 100 miles, then the changes would be harsh for 50 miles, then it would be perfect for 100 miles and so-on. I sold the car before it was properly diagnosed (the new owner was advised of the symptoms).

[koelner]

thx for your help so far! does that mean I have to live with it? i forgot to mention: the problem only occurs once the engine is warmed up.

[Mandrake]

When you do the auto adaptive reset you have to drive a certain way for about 10 miles afterwards for the adaption to work properly.

You need to perform frequent gear changes both up and down through all the gears, and also do some kick downs and rapid acceleration, otherwise the ECU won't go through enough variety of different types of gear changes to adapt properly.

I've also found it better not to do it when the gearbox is fully warmed up otherwise it can lead to harsh shifts when cold.

You say the problem only occurs when the gearbox is warmed up - what oil temperature does the Lexia report when the shifts are harsh ? Normal operating temperature is 88-94 degrees. If it is significantly over 100 degrees there is a problem causing overheating which will cause the oil to burn and degrade over time and can also lead to harsh shifting. (Due to the deterioration of the oil or burning of the clutches)

[white exec]

Just wondering whether the ATF is exactly the right spec?

[koelner]

You say the problem only occurs when the gearbox is warmed up - what oil temperature does the Lexia report when the shifts are harsh ? Normal operating temperature is 88-94 degrees. If it is significantly over 100 degrees there is a problem causing overheating which will cause the oil to burn and degrade over time and can also lead to harsh shifting. (Due to the deterioration of the oil or burning of the clutches)

that is very much in line with my car: 85-95 degrees .... thanks for your help!

[koelner]

Just wondering whether the ATF is exactly the right spec?

i used ravenol 5/4 HP fluid ... classification: LT 71141

[koelner]

one thing struck me today after reading the transmission-ecu parameters via lexia: sometimes the engine torque (nM) moves toward a subzero range (e.g. "-100nM" at idling speed). same applies to the engine-ecu: only question marks for this value (torque: "???" nM). is that normal?

[Mandrake]

Were you decelerating using engine braking when the reading went negative ? In that case it can be normal.

[koelner]

Were you decelerating using engine braking when the reading went negative ? In that case it can be normal.

ok, thx! yes, while driving in coast, at idle and low acceleration

[koelner]

for those interested: everything is fine now! i changed the gearbox ecu ... the new one has a more recent software version.
OLD:

NEW: