2008 308 1.6 petrol AL4 automatic not engaging drive and just revving, sometimes works with a battery reset.

[Squeakers]

Hi everyone,
Car in question:

2008 308 1.6 petrol with the AL4 automatic gearbox

It's a family members car and trying to help them out. Yesterday they got stranded, gearbox faulty message appeared on dash, put it into drive, press the accelerator and the car would just rev but not actually move. I disconnected the battery, reconnected and it worked first try and moved but the next time they took it out of drive and put in drive again, the issue reappeared.



The pictures will show the two gearbox faults and their further details in order from top to bottom.









Later on, I cleared these codes, rescanned and these codes appeared.







And this one the engine ECU



(this being the information about the gear interface coherence fault)



I don't know anything about automatic gearboxes since I personally have only have had manual cars so I appreciate any ideas on what the issue could be, how to solve it and what it would. I'm thinking it could be to do with the coherence faults on both gearbox and engine ECU causing it and that it isn't a mechanical issue, probably electronic. Before this, hasn't been any issues with it, works smoothly.

All the photos of the fault codes on PP2000:


Any help greatly appreciated,

Kind Regards, Chris

[GiveMeABreak]

Chris - please upload your images directly to the Forum (using the Full Editor & Preview button below, press attachments tab, then browse phone or PC for images and place them inline where you want them to appear), as it's difficult for people to keep navigating away to third party sites to see images and then keep switching back - and in any case the link is blank and the other images are not appearing, so I can't see any detail of what you have posted.

If you have any fault codes, please put them up along with the VIN (please post your VIN in full without spaces - it will be automatically masked from public view after submitting your post & will only be visible to staff).

[xantia_v6]

If a significant fault is detected in the gearbox, it should drop into limp mode, giving permanent 3rd gear and reverse. The given symptoms seem to indicate that limp mode is broken, which is not a good sign.

Try removing the fuse that feeds the transmission ECU to see if that makes limp mode work.

[wheeler]

Yes an AL4 with pressure regulation faults logged would normally point to new electro valves required but normally this caused the gearbox to go into backup mode rather than loss of drive.
Is there any signs of oil leaks underneath?

[Squeakers]

Hi there,

Thanks for the replies and apologies for the incorrectly uploading the photos but thanks for letting me know to do it, think I have figured it out.

When I first scanned the gearbox, I got this:

gearbox fault codes

Here are the details on the pressure regulation one:

gear box fault code 06 - fault in pressure regulation

and the details of the converter lockup one (although, I have seen this code before when I had to scan this car about 6 months ago and then it still drove around with no issues at the time)

gear box fault code 70 - converter lock up

then I checked the engine ecu and found these fault codes:

and details of the gear information coherence one:

engine ecu fault code - u0404

I reset all the codes, rescanned and this new one appeared on the gearbox:

vehicle speed information consistency - coherence

details of that code:

fault code 90 of vehicle speed information consistency - coherence

Since then, the codes were cleared again, car was taken for a test drive. It drove perfectly for about 1/2 mile, changing gears no issues. came to a stop, then the engine just revved very high and only very slowly creeped forward. after turning the car off and on again twice before it pulled away as it is supposed to and just went straight back home. The family member who's car it is has said it has been just like that having no issues on the move but playing up once you come to a stop and only way to fix is turning it on and off again, which has limited success and could take multiple attempts.

I have not been able to read the codes after this drive today yet but will do soon. Not sure exactly what could be causing this issue but any suggestions appreciated.

Kind Regards, Chris

[Squeakers]

Also here is the VIN as asked: VF3**************[VIN obfuscated, can be read by forum staff]

[Squeakers]

Update:

The issue is to do with the oil pressure in the gearbox. Upon starting the car, the pressure matches the guide pressure perfectly fine. When putting in drive, pressure still good, car is able to pull forward no issues, as soon as it goes back into park or neutral, it fell to about 1.5 bar and continued to fall, even as low as 0.50bar at one point, when this happens and you put into drive again, car does not pull away at all, revving up to 3000rpm and gearbox faulty pops up and goes into limp mode but car is basically immobile since the pressure is so low it can't pull away.

When you restart the car, it goes out of limp mode, pressure is back to normal, we decided to go for a drive and i was monitoring the pressure on the PP2000 laptop, for about 2 mins it worked perfectly fine in drive, pulling away, changing gears, pressure matching guide pressure, even came to a stop at one point and it pulled away. However, after those 2 mins, the oil pressure started to fall below the guide pressure and the gearbox went to limp mode and when coming to a stop, since the pressure was way below guide pressure, it couldn't pull away. Once you restart the car, pressure returns and you can drive for another 1 min or 2 before it will fall again with pressure falling away below guide pressure etc.

So issue is the oil pressure, anyone any ideas what is causing this?

Car at idle when you first turn it on, matches pressure fine.

While stationary at idle, going from park to drive back to park;

^ at this point here, the pressure falls and the car is unable to move.

While driving, first few pics driving fine, matching pressure

Then it fell and continued to fall (to a lowest of 1.1bar while on the move but not pictured)

^ and when the pressure falls, the car cannot move if you come to a stop and while on the move cannot accelerate at all because pressure so low. have to restart car to be able to move.

Then this fault code after that drive:

Any ideas and help greatly appreciated, thank you

[xantia_v6]

The obvious question is whether there is a sufficient quantity of fluid in the transmission?

[ozvtr]

Sticking pressure modulator valve by the look.
Look at the guide pressure, oil pressure and activation time.
When the modulator valve fails, there is no pressure regulation, even when the valve is driven to 100%. That means the gearbox ECU is driving the valve to 100% to try and increase the oil pressure, but there is still no pressure regulation.
However anytime the modulator valve is working, you can see that the gearbox ECU does not need to drive the valve to 100% to get pressure regulation. And the modulation % changes with the required pressure.
Could be low oil, but you would get "surging" as you drove the car along.

[Squeakers]

Hi there,

Firstly, thank you for the replies.

How would I be able to check the oil level in this gearbox? Just to note, no oil leaks from this car and gearbox, 59k miles and the auto gearbox has been working perfectly fine for the last 2 years and 10k miles and then this issue suddenly appeared and got dramatically worse in a matter of a week with the car now unusable at the moment. Not exactly expecting it to be low but is good to check if its possible.

Also, about the pressure regulation solenoid, I did the actuator test on the pressure solenoid on PP2000, it said to listen for an audible 'knocking' while all i heard was a buzzing sound. Normal or something wrong?

I also noticed that the activation time was always 100% at idle even when matching the pressure but was never 100% while moving at any point, not sure if this helps.

Seems whatever is wrong will be a bit too big a job to get involved in to solve myself on this one unless it just low on oil but that is the only hope.

[ozvtr]

How would I be able to check the oil level in this gearbox?

This process needs to be done with the car level with the engine and gear box warmed up and the engine running.
On the very bottom of the gearbox on the left hand side is a 8mm by 8mm square plug. Note:it might be a recessed plug with an Allan Key fitting!! Undo ONLY the plug and check the colour of the oil that comes out. Only a few ml of oil will come out, not all the oil. On the top of the gearbox, again on the left hand side is another 8X8mm plug. Undo this plug and pour in about 100 ml of your chosen oil*. If the oil level is correct, about 100 ml will come out of the plug hole in the bottom. If not, it's under filled. You need to decide if you are going to drain the oil or continue to "top it up"?
The colour of the oil will determine if you are going to top up the oil or drain it. Oil from the factory is amber in colour. If it has been changed at some time, it will most likely be red!

Also, about the pressure regulation solenoid, I did the actuator test on the pressure solenoid on PP2000, it said to listen for an audible 'knocking' while all i heard was a buzzing sound. Normal or something wrong?

It buzzes! And when the gearbox is in anything except park or neutral and the car is running it will buzz then too. You will be able to hear it over the engine noise!

Seems whatever is wrong will be a bit too big a job to get involved in to solve myself on this one unless it just low on oil but that is the only hope.

replacing the solenoids requires removing the valve body. Reinstalling the valve body usually requires careful alignment of a couple of components. Not for someone without experience.

[lcwin]

The pressure regulating solenoid could be faulty or the solenoid seal is leaking. Change both solenoids and seals and also 2 more seals that couple the valve body to the gearbox.