C5 with AL4 Gearbox Fault

[samson1886]

Hello to everyone....

I have an issue recently on C5 gearbox.
Things were running fine until recently when on the road, it suddenly have clonking (changing gear to 3rd, iguess) and resulted the car loss power. The screen in dashboard indicate Gearbox Fault or something like that...
I have try several options, disconnect the battery for hours, check gear oil level as well as changing the gear oil as well. but no improvement shown.

I have get it diagnose with Lexia (V1.4.13) and it tells several faults as shown below:
1) Remote Fault, Temporary Fault Dialogue with the auto g/b. incorrect value received
2) Remote Fault, Intermittent Fault Engine speed incorrect value received
3) Remote Fault, Intermittent Fault Vehicle speed incorrect value received

I've cleared the faults and have it tested on the road again, within 10km radius, it happen again. I notice that when the engine / gearbox warm up, it will happen and this will put the entire car loss power.

I've also checked numerous website including FrenchCarForum, specifically on AL4 box related, and this symptom bahaviour al4 does relate to the g/box were turn to limp home mode.
2 solenoid valve were mainly the culprit (Main Pressure & Converter Pressure Valve).
I took the effort to dismantle the valve body and have a look on the solenoid valve. It is written BW which i presume it has been changed before by the previous owner. However, I am not sure if the AL4 software has been updated to commensurate with the solenoid valve changes.
(Based on my assessment via numerous website & citroen forums, it does indicate that solenoid valve replacement changes is Borg Warner and the ECU software need to be updated)

My question are:
1) Using Lexia V1.4.13, does it has the capability to diagnose if the AL4 ECU has been updated?
2) Using Lexia V1.4.13, in the event the AL4 ECU is old revision software, can we updated it and where & how could we do it?
3) Please let me know if my post mortem acitivities is heading the correct direction? If not, please englighten me.

Thank you.

[robert terry]

Hi There, Sorry to pick your brains but I see there was no response to your posting and I was wondering if you have had any success elsewhere you could share. I am in a similar predicament with my 807 AL4 g/box in that I am trying to find out by the software version if it may have the new B.Warner electro valves fitted. Mine does not engage 1st gear instantly when selected but requires a few more revs, (unless I select snow mode). Please accept my sympathy if you are still having problems, I know how it feels,
Best Regards,
Bob.

[Mandrake]

Hi Samson, I missed this post the first time around, but I can answer some of your questions.

1) Yes, a Lexia can check the current software version of the gearbox. This is done in the Diagnosis section, under gearbox, information.

2) Yes, a Lexia can update the software version of the gearbox ECU. This is done in the Downloading section. In the download section there is also a list of software updates that are available for the various different ECU's - by comparing this to the current software version you can see if the box is running the most up to date software version or not before attempting to update it. The software updates have a one line description which briefly describe the purpose of the update.

3) If the solenoid valves have been changed to the later type then yes I believe a software update is mandatory for correct functioning of the box. Performing a software update carries a certain amount of risk if it goes wrong, but I believe you can perform multiple attempts to update the software if the first fails (Don't ask me how I know... ) and if the box is unserviceable now you don't have much to lose anyway. If you update the gearbox ECU software you are also supposed to check if there is an update for the engine ECU and update it as well if there is an update - as the two ECU's talk to each other constantly and must be running compatible software versions.

I don't know without taking my Lexia out and plugging it into the car whether the version of Lexia software you have is the latest or not, therefore whether it would have the very latest software update for the gearbox.

Other observations - the fault codes that have been logged all suggest to me that there could be an electrical fault between the ECU (mounted somewhere in the engine bay, not sure where on a C5) and the gearbox. The speed sensors are inside the gearbox connected to the ECU via the external wiring loom, its unlikely both the engine speed and vehicle speed sensors are actually faulty - more likely the cable has a poor connection that is becoming intermittent as the engine and gearbox flex on the engine mountings. I would thoroughly clean the connector at both the gearbox end and ECU end with contact cleaner. (I plan to do the same on my 4HP20 soon)

Another thing I would check other than just stored fault codes is live sensor data while doing a test drive. In particular if you get a loss of power transfer I would check the rail pressure. On an AL4 this can be monitored with a Lexia in real time under Diagnostics->Gearbox->Measurements. You will find both selected pressure (the pressure the ECU is asking for) and actual pressure. (measured pressure) The selected pressure will change depending on what gear you're in and other factors, when working properly the actual pressure should track close to selected pressure. If the actual pressure falls significantly below selected pressure you have a hydraulic fault. Any pressure lower than about 1 bar and the gear clutches will slip even with minimal engine torque and no power will be transfered.

I recently ran a diagnostic on an AL4 in a C5 that was suffering from a complete loss of forward drive after less than a minute of driving which turned out to be a loss of main hydraulic rail pressure, see the following thread for full details:

http://www.frenchcarforum.co.uk/forum/v ... =3&t=41417" onclick="window.open(this.href);return false;

Hope this helps.