Another auto gearbox will not engage 1st gear.

Hi all, I have also got problem with my Citroen C3 2002 auto transmission...After driving for about 1 km. the car just stops moving as if the transmission goes into neutral but it's still in Drive...They tell me that my transmission needs replacing and I've found a secondhand one but the code number is slightly different from mine...My transmission code number is 20TP75 and the secondhand transmission that i'm looking at is 20TP75BW...Does anybody knows if these are compatible? cheers!

Hello sphynx!

The "it needs a new gearbox" sounds just like someone who doesn't know how to solve the problem with the box you have. A bit of a brush off really, oh well.

Seeing as your car drives, it feels as if the box is overheating.

I guess you tried the easy stuff first, drain and refill the fluid? You can tell a fair bit from the colour, smell, texture of the old fluid compared to the new stuff.

As for the model numbers, not much help from me, sorry. My suggestion is that more letters after the numbers refer to modifications to the original design. (improvements on the original design like better bearings etc..)

Had you considered getting your faulty box repaired? This way you will be sure that its going to fit as its your original box.

Hi Arfur,

Thank you for the reply...

Yes I have replaced the transmission oil (Dexron III) but the old oil
looked and smelled normal.

Getting it repaired is going to cost me around $4,000 that is why I decided to
try and find a secondhand one instead.

I was also wondering why there are no error light on the instrument panel to indicate
fault with the transmission?

Would this be electrical related or mechanical fault?


Cheers!

Hi sphynx

Later versions of the automatic box have included modifications to the refilling and level checking. Later versions have the drain plug omitted meaning the unit is "sealed for life"

I would assume the different model numbers indicate the different filling and drain versions.

On earlier versions (as your 2002 model is) there is a drain and level check plug at the bottom of the gearbox. The warning is to only remove the level check plug when checking the level.

According to the haynes manual the filling plug is under the air filter, requiring a square section tool to remove.


Draining is aided by bringing the fluid to normal working temperature with a drive first.

Level checking is completed by bringing the fluid to normal working temperature with a drive
Select 'Park'
Clean the area around the filling plug to stop dirt entering the gearbox
Remove the fill plug and add half a litre of auto box fluid to the gearbox, refit the plug.
Start the engine and remove the level plug (not the drain plug) - its a 2 part plug on early models.

"The drain plug requires a 27mm spanner and the level plug requires a 19mm spanner."


For level checking use the 27mm spanner to hold the plug tight while using the 19mm socket to unscrew the level check nut.
To drain the system use the 27mm socket to remove the whole level/drain plug assembly.


Allow for the half a litre of extra fluid to trickle out (its going to be HOT).
when the trickle and drops stop, the level is correct.
If no fluid runs out, add half a litre more and try again.

Clean around the drain and fill points before removing them, catch the fluid in a container, wear plastic gloves to avoid the hot fluid.

top up with Esso ATF 4HP20-AL4 or Esso LT 71141 (mobil ATF 4HP20-AL4 or mobil LT 71141 - there is plenty of it on eBay.


Dexron III must NOT be used in the AL4/20TP75 automatic gearboxes used on the Citroen C3


It looks like its possible to reset the parameter in the gearbox ECU by disconnecting the battery for some time.

Faults recorded by the ECUs in the car do not always notify the driver. They store the error codes in memory which can be accessed by the citroen dealer or a patient DIY technical car enthusiast with access to a laptop and a Lexia tool, its a tool well worth investing in time and money for a C3 owner.

Several different faults are indicated by flashing the of the snow and sports lights (including old oil warning)

It would be worth having the garage read the codes from the automatic gearbox as these may give a bit more of an understanding of the fault. Or have a go yourself with the lexia

This is MOBIL GEAR OIL ATF LT 71141 - 558.34.22 for the C3 automatic (not sensodrive/flappy paddle).

Hi C3CAR,

Thank you very much for the info. You seem to know a lot about
These automatic gearbox (20TP75)

I was wondering if you could give me a bit of an idea on how
does the transmission oil gets cooled? I'm only used to seeing
Transmission with oil lines that goes into the radiator (oil cooler)

The transmission on the citroen c3 however just totally lost me
because it does not have oil hoses/lines going into the radiator.

It seems to me that there are 2 coolant hose leading into the
side of the transmission which makes me confused on how the
transmission oil gets cooled.

Cheers!

Hi sphynx,

The oil cooler should be mounted on the rear of the gearbox housing. (You may need to remove the battery and battery box to gain access).

Its a flat square box with two coolant pipes connected to it.

The gearbox oil is transferred from the gearbox to the cooler (oil/water heat exchanger) where the cooler meets the gearbox (no pipes required for the automatic gearbox oil) and the coolant is delivered by rubber hose and returned to the cooling system by another rubber hose.

If you remove the cooler from the gearbox expect some auto gearbox oil to spill (make sure the area is clean to stop dirt getting into the gerabox).

Clamp the coolant hoses to reduce coolant loss

If you disconnect the coolant pipes, expect to loose some coolant and the need to top up the antifreeze/coolant.

The AL4 oil cooler and coolant pipe connection detailed in red (number 5) I hope this helps.

Hello C3CAR,

Do you know if it's possible to totally fully drain all the old oil in the transmission including the torque convertor etc. so I can put new oil in?

I have done this before but on the older style automatic transmission where the oil cooler is built into the radiator (I just disconnect 1 of the oil hoses leading
to the oil cooler, start the engine then catch the old oil in a bucket as it pours out. At the same time pouring new oil into the filler point. I just then wait for the new
cleaner oil to come out into the bucket then it's all done)

Thank you C3CAR for your very valuable responses.


Cheers!

Hi sphynx

Getting the oil up to temperature by driving it, then removing the 27mm drain nut seems to be the answer to drain the system down by about 4.5litres

But, as you say - totally drain down the remaining 1.5 litres from the torque converter is going to prove quite a lot of work as you have to separate the gearbox from the engine to be able to remove the torque converter to drain it.

HHhhhmmm....It looks like I will have to remove the transmission then (that way I can have a quick look inside the transmission to
see if I can pick up on any obvious damaged or worn parts) Then decide whether to repair or replace it...

Thanks a million again C3CAR, I just hope we could have a beer together.


Regards,
Sphynx.

Hi sphynx,

A beer sounds like a great idea. (I think you are going to earn one from stripping out the gearbox)

Just an idea before you remove the box from the car, seeing as it still drives. Is it at all possible to get the codes read from the ECUs by a citroen garage?

The computer may have stored some codes (or not stored some) which can focus your attention on particular areas of the gearbox. It may just be that needle in the haystack that you are looking for.

Its not possible to get the box up to temperature and read the codes with it removed from the car.


A cheeky request:
Any chance of some photos please? of the key parts while you remove and when its removed?

Good Luck!