6T40 Transmission issues.

b3vcard

Newbie
Joined
May 29, 2024
Messages
10
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Make
Vauxhall
Model
Astra
Year
2010
Miles
95000
Engine
1.6 Petrol - A16XER
Car: Vauxhall Astra (European Cruze or Malibu basically)
Engine: 1.6 petrol (A16XER).
Gearbox: 6T40 - GEN 1 I believe.


Hi,

Have been having issues with my transmission since I bought this car last year. When stone cold it shifts fine but when warm and running it shifts hard from 3-4 or 2-3 also the downshifts are hard and jerky from 4-3 or 3-2 depending.

This all came to a head yesterday when I was driving 200km and the engine light came on, transmission select flashed and I lost reverse-3-5. Had to limp home on 1-2-4-6.

The codes I got are below;

P0776 - Pressure Control Solenoid Valve 2 Stuck Off
P0843 - Transmission Fluid Pressure Switch 1 Circuit High Voltage.

I did some research and presumed this issue was the dreaded 3/5/R issue with the waveplate in pieces.

I decided to try my luck this morning and the car now works again in all gears!

Any idea based on the return of the gears what this could be? Could I be lucky enough to just have to change the solenoids to resolve? I cannot understand how dodgy solenoids alone could cause these hard jerky shifts always in the same gears. I would have presumed the failure mode would have more been they stick on or off for long periods.

I have an advanced scantool and I originally believed the clutches were going because of below data:
1716981865749.png

Thanks,
Barry.
 

bp042665

transmission guy
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Location
Iva South Carolina
sound's like a Valve Body and a circuit problem the P0776 is a valve problem and the 843 is the pressure switch either the diaphragm or the circuit board which is built into the solenoid body assembly i change them both when i see them codes
 

b3vcard

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sound's like a Valve Body and a tcm problem the P0776 is a valve problem and the 843 is the pressure switch either the diaphragm or the circuit board which is built in the TCM board
Thanks for the reply. OK, I guess only way to find out is to take it out and see. Luckily with this small engine I can do all of this without major disassembly.

As long as its nothing within the transmission itself I am in luck! Anything in the transmission and the parts are too difficult to get, plus the complexity so the car would go straight to the junk yard.
 

b3vcard

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you can do this in the var i would recommend a sonnax for this i believe you can buy it from them with both as a assembly
Regarding the valve body, what exactly goes wrong? I looked up the diagram of it and would it not be possible for me to take it out, take it apart and just clean any valves/o-rings etc?
 

bp042665

transmission guy
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what happen's is the valve will wear the bore out and it will either get stuck or cross leak the pressure out and then it set's code for the solenoid switch valve code
 

b3vcard

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Very interesting, thanks! So if I was to carefully open the valve body open I might be able to see these bores worn out? Or are we talking very minute differences in the diameter?

As a matter of interest, if it was a clutch pack issue (Worn clutches say) - would the symptoms be different?
 

billr

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Yes, there are many tight-tolerances in there, and down deep in the bores in some cases. You may be able to see gross wear, but these are the kinds of parts that can only be checked reliably with air-gauges (or better).

If you haven't done so already, go to the Sonnax web-site and see what they have regarding tech info on this particular VB. What common problems there are with it and what upgrades they have developed to make a replacement VB "better than new"

If you do go for a rebuilt VB, be cautious if you are shopping for best price and find listings for a VB with "Sonnax upgrade". There are often several areas of a VB that needs upgraded, and some low-cost rebuilders will only install the one they feel is necessary (or cheapest). Their product may have a "Sonnax upgrade", but not all of them. I would only buy from a vendor that installs the full Sonnax "Sure Cure" kit.

PS: If you do decide to disassemble the VB, be slow and cautious, there are many small parts in there that want to fly out and get lost.
 

b3vcard

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Yes, there are many tight-tolerances in there, and down deep in the bores in some cases. You may be able to see gross wear, but these are the kinds of parts that can only be checked reliably with air-gauges (or better).

If you haven't done so already, go to the Sonnax web-site and see what they have regarding tech info on this particular VB. What common problems there are with it and what upgrades they have developed to make a replacement VB "better than new"

If you do go for a rebuilt VB, be cautious if you are shopping for best price and find listings for a VB with "Sonnax upgrade". There are often several areas of a VB that needs upgraded, and some low-cost rebuilders will only install the one they feel is necessary (or cheapest). Their product may have a "Sonnax upgrade", but not all of them. I would only buy from a vendor that installs the full Sonnax "Sure Cure" kit.

PS: If you do decide to disassemble the VB, be slow and cautious, there are many small parts in there that want to fly out and get lost.
Thanks for that!

This Sonnax website is really good. Unfortunately it has a symptom checker for the 6T40 and just lists the 3-5-R Drum Saver (Wave plate) as the resolution for P0776.

Surely I would not be getting the 3-5-R gears back if the wave plate went bye bye?
 

billr

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I expect doing the wave-plate involves digging deep into the trans guts; but you will have to wait for one of our trans experts to comment on what effects it can have. My guess is that a bad wave-plate would not smooth a shift (clutch engagement) properly, but would not prevent a shift completely. Wait for the experts to chime in...

BP and grc, do you think air-checks could help figure this out?
 

bp042665

transmission guy
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when the wave plate breaks you will feel a bind up based off the info you have provided im chasing a valve body and maybe a tcm but if you do pull trans i would have the wave plate replaced
 

b3vcard

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Ok, have an update and its not a good one unfortunately.

As I am in Ireland I could not get a sonnax part quickly so just decided to get amazon parts. (Most likely Chinese used or aftermarket).

-I removed the TECHM and valve body as per instructions online, it wasnt difficult but messy.
-I replaced the solenoids in the TECHM and that went smoothly.
-I then replaced the valve body in the car. Initially I put it in without properly putting the slider pin in the manual valve so I had to remove it again to do that. I then put it all back together.
-The car ran fine and I had reverse but no forward movement. The cluster said it was in "D" but no movement. I could also put it in M1,M2 and M3 but nothing.

-I thought I did something wrong so took it all apart again and looked at the Techm and valve body, saw no issues, reassembled and tried again but nothing.
-I swapped to my original solenoids then and tried but nothing.

-Finally I have gone back to all original parts but still have no forward movement.

This article below said this is a common occurance and its due to incorrect manual valve position, but that was ok for me.
Also it gives a test where you put the car into neutral and then take out the transmission connector at the front. The car is then supposed to move forward. Mine does slightly but it wouldnt actually drive, its only a feint pull.


At this point all I can think is the techm somehow blew internally? I just don't know what I could have done.
 

b3vcard

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One thing I have just learned is that the manual lever switch is not supposed to be best but rather straight. It's possible I bent it backwards in my first installation, would this cause no drive?

Surely if this was very off it would also cause no reverse. The second picture is the park position
 

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b3vcard

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I will get back on the pressure items from the stcan tool.

I have had a breakthrough though! I followed on from my theory of that pin being bent and not putting the manual valve into the proper position. So I put the car into drive and then pushed the shift lever further on. I didn't realise but there is one more notch it can go into. This puts it into "M" mode on my cluster.

Then the car moved! It can actually move by acceleration etc. Although I did not go far.

I am leaning on the idea that that pin in the transmission needs to be bent back so that when in Drive it actually has the manual valve in the correct positon. Won't be the easiest as I am doing it from above but at least its some sort of breakthrough I believe!
 
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