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Going into 3rd gear is called STOPPING MODE its the auto box's way of preserving itself in 3rd hydraulic these gear boxes are quite complex they have a valve body inside which controls your gear changes these are a group of sequence valves, they also have two other valves known as the BORG WARNER VALVES (mentioned extensively on this site) these are a lock off and a pressure regulation electro valve, there are six levels of DOWNGRADED MODE and many things can cause these issues from the brake switch mentioned above to blocked filter, when I first worked on the AL4 auto box I spent a lot of unnecessary time and money trying to eliminate each individual part of the gearbox, as you say yours keeps going into third hydraulic then according to the manual then it can only be in level 5 or level 6 of downgraded mode as these levels are the only time out of the 6 that it will switch itself to 3rd gear. Below are the possible faults that it could be according to the manual. - THROTTLE POTENTIOMETER INFORMATION -ENGINE TORQUE INFORMATIONMULTIFUNCTIONS SWITCH -SUPPLY TO ANALOUGE SENSORS -PRESSURE MODULATING ELECTROVALVE -MAIN PRESSURE REGULATION -HEAT EXCHANGER OIL FLOW MODULATING ELECTROVALVE -INPUT SPEED AND OUTPUT SPEED -INPUT SPEED AND ENGINE SPEED -OUTPUT SPEED AND ENGINE SPEED -ECU NOT WORKING -SEQUENCE ELECTRO VALVES - SUPPLY TO SEQUENCE ELECTROVALVES - ACCELERATOR PEDAL NOT PROGRAMMED Now the question you will be asking yourself is how do you determine out of that list what the problem is ? Well the answer is always the same LEXIA diagnostics the advantage of this the gearbox has its own ECU and it will give you either a fault reading as to what the problem is or via the live parameters this will at least narrow it down to a few, the most obvious thing to me reading you symptoms is either the lock up electro valve or the pressure regulation valve these are common problems with these and are quite simple to do your self there is a lot of info on here that will guide you, Regarding the ATF change this does help but doesn't cure many issues once your limit counter reaches its limit the on board computer will tell you its time for a change and as mentioned above even this isn't straight forward and you do need LEXIA to complete this for two reasons the first being to have the gear box at the correct temperature not the gar the AUTOMATIC TRANSMISSION FLUID and the second being to set the counters back to zero this allows the auto box's ECU to let the car know its has X amount of miles before the next ATF change. if I can be of assistance in any way I would be glad to help.

PROCEDURE FOR battery DIS-CONNECTION (The 3 Minute Rule) Whenever a vehicle battery has to be dis-connected, switch off all equipment, interior lights etc, close the doors leaving the drivers window open. Switch off the ignition and remove the key and any DIAG equipment. Wait a full 3 minutes before disconnecting the battery. The BSi must be allowed to go to SLEEP i.e. into "power save mode". Do not operate any equipment on the vehicle during this time. Remember, even opening the bonnet will wake the BSi on a vehicle fitted with alarm. If the battery is under the bonnet, open the bonnet first and leave it up. C8 batteries can be dis-connected through the drivers window, remove floor cover first. (note, Pics are under the passenger seat) ALWAYS disconnect any DIAG equipment and do not operate any plips from other vehicles during the 3 minute waiting period. PROCEDURE FOR battery RECONNECTION Unless otherwise instructed by Product Service, you must always carry out the following procedure, often referred to as a "soft re-boot", to minimise the possibility of the BSi corrupting its own software when reconnecting the vehicles battery supply. Ensure the procedure for battery disconnection has been adhered to and importantly all BSi functions were switched off with the drivers window left down. 1 Close all doors 2 Remove ignition key if left in ignition 3 Reconnect battery. DO NOT open any doors 4 Wait 10 seconds 5 Switch on headlights through the drivers window (you will hear a "bong") (note: Snap-on says Side-lights) 6 Switch on ignition then start the vehicle and check system functions NOTE: Upon reconnection, if any vehicle function controlled by the BSi i.e . interior light is switched on,the internal operation of the BSi has the potential to spike or corrupt its configuration and software program....

Yes, you will need to get this on LEXIA this will give your A/C system an individual scan and the advantage of this is it will give you a plain old English fault reading no codes a live reading of what the fault is. It will probably be the A/C PRESSURE SENSOR, check that the A/C HIGH SPEED FAN is kicking in as if this isn't happening it can cause high pressure, PRESOSTAT, BLOCKAGE IN THE EVAPORATOR, or like you said the RELAY test this by taking of the plastic casing and manually operate the connections if the compressor doesn't kick in then there is no electrical supply. where about in the UK are you?

nice one i apreciate it and yes if in the future it gives me grief i shall check this out before i disregard the MPLS completely as these can so easialy be over looked. All in all so so happy, thanks again.

Just an update on this completed the multi function switch adjustment and eveything is brilliant, really pleased with the outcome took me around 30 mins start to finish quite easy actually although the paper looks the complete opposite. Thanks for your imput SIMPLE really helped out if i can help anyone out with any of the stuff mentioned in this thread then let me know and i will try to assist. Thanks again.

Hi and thank you for your reply some useful info there, the replacement of the electro valves was done to the T and like I said the gear box is operating better than it ever has I have just noticed on this paper https://www.petrila.net/repair/2/406d9/info/gb/b2cg6sk3.htm that it states the adjustment of the multi functions switch is imperative after replacement of the electro valves so I will now follow your paper and report back to you tomorrow and see if it worked thanks so much again.

I done this once on a 407 i took it out pressure washed it i then drilled a hole with a 2inch core drill through it so that the ECU couldnt detect back pressure and trigger a regen and put it all back together I then sent off the ECU to my friend Steve at HDI tuning and had the DPF deleted this in turn makes the ECU think it doesn't have a particulate filter and also stops the Eloy's fluid process. As far as MOT is concerned there is no real way the tester can check and they are very unlikely to strip it down and check. the next Mot for mine passed the emissions test with flying colours and also gave me better MPG and 5 more BHP. NO DPF NO PROBLEMS.

Hi I am not far from you and have LEXIA I would be willing to come by and try and help you solve this issue I am under the impression than the airbag ECU is the same across all models you mentioned above but like any ECU they will need re-learning and a possible update failing that I know that the impact sensors/satellite sensors are a common prob on these but without the correct diagnostics equipment like any PSA you are in the dark and can end up making problems worse trying to find a minor problem.

just changed the dreaded pressure regulation and lock up electro valves on my c8's al4 autobox along with the complicated ATF change. I also set the counters back to zero via lexia. took it for a spin and the results are perfect running like a new car. I am new to this particular forum and am aware from previous forums i have been a member of that the sharing of information and outcomes is important so if anyone is experiencing these issues then i would be more than glad to help and have plenty of notes on this procedure. When I was on my test run I did notice that my led screen was showing a discrepancy between gears i.e if I was in drive the led would say neutral. I now no that this is the multifunction switch needing adjusting it had no baring on the drive what so ever it was faultless. I just wanted to know if anyone on here had done this procedure and had any tips for me before I attempt this tomorrow. kindest.