Everything about your ZF automatic transmission issues

I have found this amazing article about the transmission in BMW E90’s so I’m re-posting it here in my blog with updated pictures and part numbers to match ZF 6HP21.

So if you want to maintain your transmission you should read it even if you don’t have any problem in your transmission right now.
Credit goes to : BMW Logic7 site

It applies to all BMW with ZF 6HP19/ 6HP19Z / 6HP21 aka GA6HP19TU
In this post i will be explaining why you have transmission issues like:

-harsh shift 2-1

-not able to shift into park when hot

-weak torque feeling

-transmission faults

All highlighted problems you can experience even on low miles cars less than 70-80k, it depends on at what speeds your car mostly runs. On the highway this transmission will easily last 200-300k miles.

So you hate the way transmission shifts and workshops didn’t find any faults and they told you it is what it is and this is how it is intended to work!

In fact ZF 6HP21 is a very good transmission, powerful, bullet proof pretty much if serviced in time and proper fluid pressure maintained! This transmission is still considered one of the best and has carbon clutches vs cheap paper ones you can find on Japanese cars. But this transmission has very serious and very important weak spots you have to take care of:

-First thing first, check transmission temperatures

If it is higher than 95C, then most likely you have a problem with transmission cooling system or your engine cooling has some leaks causing running it very hot.

Usually high temps indicate following:

1) engine cooling system problem- air bubbles or airlock.

2) if everything is good with cooling system, check your transmission oil cooler- it gets clogged up pretty often and also indicates that some clutches or Torque converter clutch is worn out and that debris clogged oil cooler.

3) worn out Torque converter clutch slipping overheating transmission fluid.

Your good engine temps are 103-105C and if it climbs to 107-110C in traffic, it means you’ve got a leak :

-lower radiator hose sensor leaking (usually shows a white residue around the sensor).

-valley pan under intake.

-rear cover plate between transmission and engine. Very common after 100k or 8-10 Years.

-coolant tank cracked.

-radiator cap leaking pressure.

-coolant pipe seal leaking.

-other cooling issues.

It is very important to keep temps in specs not only because of few degrees, but because with leaking cooling system lose coolant pressure introducing air in the system, causing uneven cooling and overheating both engine and transmission. Good OEM specs are 103-105 cycle when idling and lower hose should be hot around 60-80C. When you drive it tstat is controlled by ECU therefore it keeps it cool on the freeway.

Easy way to test your cooling system

1)Disconnect aux pump connector assuming aux pump is working (they fail often).

2)Drive your car to warm engine well.

3)Turn on heater on hot but low speed.

4)check if you get hot air from vents for 10 minutes.

5)If after a minute you noticed your heater is not hot anymore, it means you’ve got a leak!.

6)This Engine has self bleeding cooling system, which means you cannot get air pocket if system is well sealed.

So if engine temps are good and transmission still runs hot 100-110, it means heat exchanger is clogged with transmission clutches, Torque Convertor wear and tear dirt. Replace it and check if it got better. This transmission will die quick if temps are not good.

– MECHATRONIC Adapter Seal

This adapter (number 2) usually lasts only 60-70k miles. Replace it every 60k miles even if transmission shifts well. It is very important because it keeps your mechatronic valve body under specified pressure therefore it controls how clutches are pressed! Which means if your gasket is weak your transmission clutches are not pressing well on each other causing premature wear and tear, also transmission pump and TC clutch will be affected.
This square seal also can crack, in this case you will get transmission fail safe errors and even clutches slipping errors, causing very quick transmission death. don’t drive your car if you’re getting any transmission faults, even after restart transmission errors go away for a while, it is not a transmission computer glitch!!!

Mechatronic Seal Adapter late 6HP19 & 6HP21
BMW part number : 24347588724
ZF Part number : 0501 215 783


-4 Rubber Seals

They are 5,6,7 also controls clutch pressure, but even if they are flattened, pretty bad transmission won’t give you any errors. Its always good idea to replace it- you’ll notice a difference how your transmission shifts.

BMW Part Numbers:
24107536339 x 2

ZF Part Numbers:
0501 319 279 x 2
0501 319 280
0501 319 281

-SOLENOIDS (Pressure Regulators)


Yes they go bad and are not simple solenoids you used to know from old school transmissions. Now these are pressure regulators and they do not only work open\close operation, they control pressure and after so many time they get clogged, overheat, etc. So if your transmission temps are good and your transmission shifts hard, it could be your solenoids. Its good idea to replace them every 100k, because they control everything in the transmission. You will be surprised how transmission shifts with new solenoids.Also don’t be scared if you open your transmission and find out that color is not the same- relax it changed color because of temps and age.

Unfortunately ZF does not sell the SOLENOIDS kit, you have to hunt for it in some online sites.
You can see that in the parts catalog:




and you need to replace the protection foam strip with the solenoids:

Protection Foam Strip:
ZF: 1068 327 241

A useful document for replacing the solenoids can be found here:

A video I made to replace the solenoids:

-Giubo (FLEX DISC)


BMW part number : 26117610061



Driveshaft Centering Sleeve / Guide bushings
BMW part number : 26117526611

They usually go bad after BMW lifetime period 60-70k.

Common Symptoms:

a) hard 2-1 shift

b) at stop you can hear clunking when shifting from P-R-D

c) overall transmission shifting quality

Check this amazing article: How To Properly Install Driveshaft Flex Disc (Giubo)

-transmission fluid level

Yes due to leaking oil pan gasket you might loose some fluid. Always check transmission oil pan for leaks and transmission fluid level (use BMW sealed transmission fluid level check procedure).

-Torque converter

02/06 – 03/07 ZF: 4168 025 487
01/07 – 08/07 ZF: 4168 025 553

Yes it can go bad just like any clutch, because this transmission engages this clutch very early causing premature wear and tear.it can engage clutch as early as at first gear!! That’s why we get decent mpg from this transmission. In other words it is more like a manual transmission with torque converter working only at very low speeds and low rpm. So I would NOT recommend driving it very aggressively in the city, unless you enjoy paying 4-5k for a new transmission. Don’t forget this transmission handles 300-400hp and some impressive torque. Driving in normal mode, Torque converter can last up to 300k miles!!

most common symptoms of bad clutch:

-sometimes when clutch is very bad it will throw 1721 error clutch slip.

-bad MPG. Without TC clutch your car is still drive-able, but you can feel its very weak even though engine feels strong

-after 4th gear tachometer arrow is not steady

-weak pickups, downshifting when driving uphill

-bad slipping clutch will overheat transmission pump and finally will kill internal transmission parts (clutches, valve body, seals, etc)

You can have your Torque converter rebuilt for around 300$, its not as perfect as new, but decent still.

Its a long list of issues, but if you take care of your transmission every 80-100k miles it pays for itself pretty good. Most important thing for this transmission is correct fluid pressure and temps, other parts like clutches are very durable and made with highest quality standard. Don’t forget the same transmission they still install on newest Bentley, Rolls Royce, Audi, Maserati and other luxury brands. This transmission is way more reliable than Mercedes one or Lexus transmissions.